Glossary of medical terms

From WikiMD

American medical association (AMA) glossary of medical terms. Also see

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AMA Glossary of Medical Terms (Source: ) 


  • Abdominal cavity is the part of the body between the bottom of the ribs and the top of the thighs, containing most of the digestive and urinary systems along with some reproductive organs

  • ABO blood groups is The system by which human blood is classified, based on proteins occurring on red blood cells; the four classification groups are A, AB, B, and O

  • Abortion is termination of a pregnancy; can occur because of natural causes (called a miscarriage) or be a medical intervention

  • Abscess is an accumulation of pus in a body tissue, usually caused by a bacterial infection

  • ACE inhibitor is a drug typically used to treat high blood pressure (Angiotensin-Converting Enzyme inhibitor)

  • Achilles tendon is the tendon at the back of the lower leg that connects the calf muscle to the heel bone

  • Acid-base balance is the mechanisms that the body uses to keep its fluids close to neutral (neither basic nor acidic) so that the body can function properly

  • Acidosis is a condition marked by abnormally high acid levels in the blood, associated with some forms of diabetes, lung disease, and severe kidney disease

  • Acid reflux is a disorder in which acid in the stomach comes up into the esophagus, because the valve separating the stomach and esophagus does not function properly

  • Acne is a skin condition characterized by inflamed, pus-filled areas that occur on the skin's surface, most commonly occurring during adolescence

  • Acquired is a word describing any condition that is not present at birth, but develops some time during life

  • Acute is describes a condition or illness that begins suddenly and is usually short-lasting

  • Acute respiratory disease is an urgent condition in which oxygen levels in the blood are lower than normal and breathing is difficult

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  • Addiction is dependence on a substance (such as alcohol or other drugs) or an activity, to the point that stopping is very difficult and causes severe physical and mental reactions

  • Adenitis is infection and inflammation of a gland, especially a lymph node

  • Adipose tissue is another term for fatty tissue; it stores energy, insulates, and cushions the body

  • Adjuvant therapy is the use of drugs or radiation therapy in the treatment of cancer along with surgery

  • Adrenal failure is a condition in which the adrenal glands do not produce enough of the hormones that control important functions such as blood pressure

  • Adrenal glands is two small glands located on top of the kidneys that secrete several important hormones into the blood

  • Adverse reaction is an unintended and unwanted side effect of some sort of treatment, usually drug therapy

  • Aerobic exercise is physical activity during which the heart and lungs must work harder to meet the body's increased oxygen demand

  • Affective disorder is a mental disorder involving abnormal moods and emotions; affective disorders include manic-depressive disorder

  • Afterbirth is the placenta and membranes that are eliminated from the woman's uterus following the birth of a child

  • Afterpains is normal contractions of the uterus after childbirth that usually occur for the first few days after delivery

  • AIDS is see Acquired immunodeficiency syndrome

  • AIDS-related complex is symptoms including weight loss, fever, and enlarged lymph nodes experienced by people who are infected with HIV but do not yet have AIDS

  • Air embolism is the blockage of an artery by air bubbles, which may have entered during surgery or after an injury

  • Airways is the passageways that air moves through while traveling in and out of the lungs during breathing

  • Albinism is a condition in which people are born with insufficient amounts of the pigment melanin, which is responsible for hair, skin, and eye color

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  • Alkalosis is dangerously decreased acidity of the blood, which can be caused by high altitudes, hyperventilation, and excessive vomiting

  • Alkylating agents is substances used in cancer treatment that interfere with the division of cells

  • Allergen is a substance that causes an allergic reaction

  • Allergic rhinitis is irritation of the nasal passages and the whites of the eyes, causing sneezing, runny nose, and sore eyes

  • Allergy is a negative reaction to a substance that in most people causes no reaction

  • Alopecia is baldness or loss of hair, mainly on the head, either in defined patches or completely; the cause is unknown

  • ALS is see Amyotrophic lateral sclerosis

  • Altitude sickness is headaches, dizziness, and nausea usually experienced at heights above 8,000 ft because of reduced oxygen in the air

  • Alzheimer disease is a condition that occurs late in life and worsens with time in which brain cells degenerate; it is accompanied by memory loss, physical decline, and confusion

  • Amenorrhea is absence of menstrual periods, occurring either after or before menstruation has begun

  • Amniocentesis is a procedure in which a small amount of amniotic fluid is removed from the mother’s womb in order to detect abnormalities of the fetus

  • Amniotic fluid is clear fluid that surrounds a fetus during pregnancy and cushions and protects it

  • Amyotrophic lateral sclerosis is the most common of a group of disorders known as motor neuron diseases, in which the nerves in the brain that control the movement of muscles degenerate and muscle function is gradually lost; commonly called Lou Gehrig's disease

  • Anabolic steroid is a drug similar to the male hormone testosterone that builds muscles and strengthens bones, but has adverse side effects

  • Anal fistula is an abnormal tubelike passage connecting the anus to the surface of the surrounding skin

  • Analgesic is a drug that relieves pain, such as aspirin or acetaminophen

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  • Anal sphincter is a ring of muscle fibers at the opening of the rectum, controlling the opening and closing of the anus

  • Anaphylactic shock is a life-threatening allergic reaction resulting in difficulty breathing and low blood pressure

  • Anatomy is the structure of bodies; commonly refers to the study of body structure

  • Androgen is a hormone (such as testosterone) that causes development of male characteristics and sex organs

  • Anemia is a condition in which the blood does not contain enough hemoglobin, the compound that carries oxygen from the lungs to other parts of the body

  • Anencephaly is a fatal birth defect in which the brain and spinal cord have failed to develop, resulting in the absence of a portion of the skull and brain

  • Anesthesia is a loss of sensation in a certain part of the body or throughout the body

  • Anesthetic is a substance that temporarily causes a person to be unable to feel pain, either in a certain area or over the entire body

  • Aneurysm is an abnormal swelling of the wall of an artery, caused by a weakening in the vessel wall

  • Angina pectoris is pain experienced in the chest, arms, or jaw because of a lack of oxygen to the heart muscle

  • Angioma is a tumor made of blood vessels or lymph vessels that is not cancerous

  • Angioplasty is the use of surgery to make a damaged blood vessel function properly again; may involve widening or reconstructing the blood vessel

  • Anorexia nervosa is a dangerous eating disorder mainly affecting young girls in which the sufferer has an intense fear of looking fat, avoids food, and loses weight excessively

  • Antacid is a drug that neutralizes stomach acids; used to treat indigestion, heartburn, and acid reflux

  • Antibiotic resistance is the development by bacteria of the ability to live in the presence of a certain antibiotic, making treatment difficult

  • Antibiotics is bacteria-killing substances that are used to fight infection

  • Antibody is a protein made by white blood cells that reacts with a specific foreign protein as part of the immune response

  • Anticoagulants is drugs used to stop abnormal blood clotting, such as to prevent stroke

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  • Antihistamine is a drug that relieves an allergic reaction by stopping the effects of histamine, the substance responsible for the negative symptoms associated with the reaction

  • Antihypertensives is drugs used to relieve the symptoms and prevent the damage that can occur from high blood pressure

  • Antioxidants is substances that protect against cell damage by guarding the cell from oxygen free radicals

  • Antiseptics is chemicals applied to the skin that prevent infection by killing bacteria and other harmful organisms

  • Anus is the opening through which feces are passed from the body

  • Aorta is the main artery in the body, carrying oxygenated blood from the heart to other arteries in the body

  • Aortic stenosis is narrowing of the opening of the aortic valve in the heart, which increases resistance to blood flow from the left ventricle to the aorta; commonly a birth defect or caused by scarring and calcium accumulation in the valve from rheumatic fever

  • Apgar score is a system for evaluating the health of a newborn baby; rated on a scale of 0- 10

  • Aplasia is the complete or partial failure of any organ or tissue to grow

  • Aplastic anemia is a severely reduced number of red blood cells, white blood cells, and platelets

  • Apnea is a possibly life-threatening condition in which breathing stops, for either a short or long period of time

  • Appendectomy is surgical removal of the appendix to treat appendicitis

  • Appendix is a short, tubelike structure that branches off the large intestine; does not have any known function

  • ARC is see AIDS-related complex

  • Arteriosclerosis is a disorder causing thickening and hardening of artery walls

  • Arteritis is inflammation of the walls of an artery that causes the passageway to become narrower; can lead to tissue damage because oxygen is not properly supplied

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  • Artery is a large blood vessel that carries blood from the heart to tissues and organs in the body

  • Arthritis is a disease of the joints characterized by inflammation, pain, stiffness, and redness

  • Arthroscopy is a procedure used to examine the inside of a joint using a viewing tube (an endoscope)

  • Ascites is excess fluid in the abdominal cavity, which leads to swelling

  • Aspermia is the failure either to produce or to ejaculate sperm

  • Asphyxia is the medical term for suffocation; can be caused by choking on an object, by lack of oxygen in the air, or by chemicals such as carbon monoxide, which reduce the amount of oxygen in the blood

  • Asthma is a disorder characterized by inflamed airways and difficulty breathing

  • Astigmatism is a disorder in which the front surface of the eye (the cornea) is not correctly spherical, resulting in blurry vision

  • Atherectomy is a procedure performed to remove plaque that is blocking an artery

  • Atheroma is fatty deposits on the inner walls of blood vessels, which can cause narrowing and decrease blood flow

  • Atherosclerosis is narrowing of the lining of the arteries due to the accumulation of fat and other materials; leads to coronary heart disease, stroke, and other disorders

  • Athlete's foot is an infection between the toes caused by a fungus, which leads to sore, cracked, and peeling skin

  • Atresia is a birth defect in which a normal body opening or canal is absent; usually requires surgical repair soon after birth

  • Atria is the two upper chambers of the heart; the singular form is atrium

  • Atrial fibrillation is an irregular heartbeat in which the upper chambers of the heart (the atria) beat inconsistently and rapidly

  • Atrial flutter is an irregular heartbeat in which the upper chambers of the heart (the atria) beat rapidly but consistently

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  • Atrophy is the shrinkage or near disappearance of a tissue or organ

  • Attention-deficit disorder is a disorder mainly present in children and adolescents, characterized by learning and behavior problems, inability to pay attention, and sometimes hyperactivity

  • Audiogram is a graph showing a person's hearing ability, determined from a set of tests examining hearing acuity of different sound frequencies

  • Aura is a "warning" signal that comes before a migraine headache or an epileptic seizure, which might include emotions or sensations of movement or discomfort

  • Auscultation is the act of listening to sounds within the body, such as the heartbeat, with a stethoscope

  • Autism is a mental disorder characterized by an inability to relate to other people and extreme withdrawal

  • Autonomic nervous system is the part of the nervous system that controls automatic body functions, such as heart rate, sweating, pupil dilation, and digestion; divided into the sympathetic nervous system and the parasympathetic nervous system

  • Autopsy is the examination of a body following death, possibly to determine the cause of death or for research

  • Autosomal dominant is a term describing a gene on any chromosome other than the sex chromosomes that produces its effect whenever it is present; can also describe the effect of the gene itself

  • Autosomal recessive is a term used to describe a gene on any chromosome other than the sex chromosomes that produces its effect only when two copies of it are present; can also describe the effect of the gene itself

  • Axilla is medical term for the armpit

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  • Bacillus is any bacteria that is rod-shaped; responsible for diphtheria, dysentery, tetanus, and tuberculosis, as well as other diseases

  • Bacteremia is a condition in which bacteria are present in the bloodstream; may occur after minor surgery or infection and may be dangerous for people with a weakened immune system or abnormal heart valves

  • Bacteriostatic is term used to describe a substance that stops the growth of bacteria (such as an antibiotic)

  • Bacterium is a tiny, single-celled microorganism, commonly known as a germ; some bacteria, called pathogens, cause disease

  • Bacteriuria is bacteria in the urine; large amounts can indicate bladder, urethra, or kidney infection

  • Ball-and-socket joint is a joint consisting of a ball-shaped bone that fits into a cup-shaped bone, making the joint free to rotate; examples include the hip and shoulder

  • Balloon angioplasty is a technique that uses a balloon catheter to open arteries clogged with fatty deposits

  • Balloon catheter is a hollow tube with a small, inflatable balloon at the tip; used to open a narrowed artery or organ that has become blocked

  • Barbiturates is a group of sedatives that reduce activity in the brain; are habit-forming and are possibly fatal when taken with alcohol

  • Barium enema is a technique in which barium is placed into the large intestine and rectum and then X-rays are taken to check for possible disorders of these organs

  • Bartholin's glands is two pea-sized glands that, when sexually aroused, release a fluid that lubricates the vagina

  • Basal cell carcinoma is a type of skin cancer that is caused by exposure to large amounts of sunlight; commonly found on the neck, face, and arms

  • Basal metabolic rate is the lowest rate at which a person can possibly use energy and remain alive; at this rate, only absolutely necessary functions such as breathing are maintained

  • B cell is a white blood cell that makes antibodies to fight infections caused by foreign proteins

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  • BCG vaccine is a vaccine used to protect against tuberculosis

  • Becker’s muscular dystrophy is a hereditary disease in which the muscles weaken and waste away; similar to Duchenne muscular dystrophy but starts later in life and advances more slowly

  • Bell's palsy is another name for facial palsy, the usually one-sided, temporary numbing of the facial muscles, caused by an inflamed nerve

  • Bends is see Decompression sickness

  • Benign tumor is a tumor that is not cancerous, which means it does not spread through the body, but may grow and become dangerous

  • Beta blocker is a type of drug used to treat high blood pressure and heart disorders by reducing the strength and rate of the pumping by the heart

  • Beta carotene is a pigment found in orange vegetables and fruits, which the body converts to vitamin A; possibly protects against cancer

  • Bifocal is a lens that corrects both near and distant vision by having two parts with different focusing strengths

  • Bilateral is a term describing a condition that affects both sides of the body or two paired organs, such as bilateral deafness (deafness in both ears)

  • Bile is a yellow-green liquid produced in the liver whose function is to remove waste from the liver and break down fats as food is digested

  • Bile duct is a tube that carries bile from the liver to the gallbladder and then to the small intestine

  • Biliary atresia is a birth defect in which the bile ducts are not completely developed; often a liver transplant is necessary

  • Biliary colic is a severe pain in the upper right section of the abdomen, usually caused by a gallstone passing out of the bladder or through the bile ducts

  • Biliary tract is the system of organs and ducts through which bile is made and transported from the liver to the small intestine

  • Bilirubin is the orange-yellow pigment in bile, causing jaundice if it builds up in the blood and skin; the levels of bilirubin in the blood are used to diagnose liver disease

  • Binging and purging is behavior characteristic of the disorder bulimia in which a person overeats then rids themselves of the food before it can be absorbed by the body, either by forced vomiting or through the use of laxatives

  • Biochemistry is the science that studies the chemistry of living organisms, including humans

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  • Bioequivalent is a drug that has the same effect on the body as another drug

  • Biofeedback is a technique used to gain control over a function that is normally automatic (such as blood pressure or pulse rate); the function is monitored and relaxation techniques are used to change it to a desired level

  • Bipolar disorder is an illness in which the patient goes back and forth between opposite extremes; the most notable bipolar disorder is manic-depressive disorder, which is characterized by extreme highs and lows in mood

  • Birth canal is the passage that includes the uterus and vagina through which the baby passes at birth

  • Birth control is the regulation of the number of children born, referring either to the prevention of pregnancy (by birth control pill, sterilization, etc) or the prevention of birth (by abortion, etc)

  • Birth defect is an abnormality that is present when a baby is born

  • Birthmark is any area of discolored skin that is present when a baby is born

  • Bisexuality is sexual interest in members of both sexes

  • Bladder is an organ located in the pelvis whose function is to collect and store urine until it is expelled

  • Blind spot is a spot in the field of vision that is not sensitive to light; it is a product of the entrance of the optic nerve into the eyeball, where no light receptors are present on the retina

  • Blood-brain barrier is a layer of tightly bound cells that prevents certain substances carried in the bloodstream from entering the brain

  • Blood clot is a semisolid mass of blood that forms to help seal and prevent bleeding from a damaged vessel

  • Blood pressure is the tension in the main arteries that is created by the beating of the heart and the resistance to flow and elasticity of the blood vessels

  • Blood transfusion is the transfer of blood or any of its parts to a person who has lost blood due to an injury, disease, or operation

  • Blood type is a category used to describe a person's blood according to the kinds of proteins present on the surface of the red blood cells

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  • B lymphocyte is a type of white blood cell that makes antibodies and is an important part of the immune response

  • Boil is an inflamed, raised area of skin that is pus-filled; usually an infected hair follicle

  • Bone marrow is the fatty yellow or red tissue inside bones that is responsible for producing blood cells

  • Bone marrow transplant is a surgical procedure in which defective or cancerous bone marrow is replaced with healthy marrow, either from the patient or a donor

  • Bone spur is an abnormal growth of bone out of another bone, often located on the heel and usually painful

  • Booster is an additional dose of a vaccine taken after the first dose to maintain or renew the first one

  • Botulism is poisoning from poorly preserved food contaminated with a dangerous bacterial toxin that results in paralysis

  • Bradycardia is a slow heart rate, usually below 60 beats per minute in adults

  • Brain damage is permanent death or damage of brain cells resulting in decreased mental ability

  • Brain death is the condition in which the brain stops functioning while the heart continues to beat

  • Breech birth is childbirth in which the baby is turned around in the uterus and emerges head-last instead of head-first

  • Bronchiolitis is an infection caused by a virus in the bronchioles (the smallest airways in the lungs), mainly affecting young children

  • Bronchitis is inflammation of the bronchial tubes, which connect the trachea to the lungs

  • Bronchoconstrictor is a substance that causes the lung airways to tighten up and become more narrow

  • Bronchodilator is a drug that widens the airways in the lungs to improve breathing; works by relieving muscle contraction or buildup of mucus

  • Bronchospasm is the temporary narrowing of the airways in the lungs, either as a result of muscle contraction or inflammation; may be caused by asthma, infection, lung disease, or an allergic reaction

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  • Bruxism is an unaware clenching or grinding of the teeth, usually during sleep

  • Bubonic plague is a form of plague in which lymph nodes in the groin and armpit swell

  • Bulimia is a disorder in which a person eats large amounts of food then forces vomiting or uses laxatives to prevent weight gain (called binging and purging)

  • Bunion is a hard, fluid-filled pad along the inside joint of the big toe; may be caused by wearing high-heeled shoes or a genetically weak joint

  • Burkitt's lymphoma is a cancer of lymph tissue that most frequently occurs in the abdomen, the ovaries, and the bones of the face; it is associated with malaria

  • Bursa is a fluid-filled sac that cushions and reduces friction in certain parts of the body

  • Bursitis is inflammation of a bursa due to excessive pressure or friction, or from injury

  • Butterfly bandage is a butterfly-shaped bandage that can help close a minor cut for proper healing

  • Bypass is a surgical technique in which the flow of blood or another body fluid is redirected around a blockage

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  • Calcification is the depositing of calcium salts in the body, which occurs normally in teeth and bones but abnormally in injured muscles and narrowed arteries

  • Calcitonin is a hormone made in the thyroid gland that controls calcium levels in the blood by slowing the loss of calcium from bones; used to treat hypercalcemia (excess calcium in the blood)

  • Calcium is a plentiful mineral in the body and the basic component of teeth and bones; essential for cell function, muscle contraction, transmission of nerve impulses, and blood clotting

  • Calcium channel blocker is a drug used to treat chest pain, high blood pressure, and irregular heartbeat by preventing the movement of calcium into the muscle

  • Callus is a thickened area of skin due to consistent pressure or friction, or the area around a bone break where new bone is formed

  • Calorie is a unit that is used to measure the energy content in food

  • Canal is a tunnel-like passage

  • Cancer is a group of diseases in which cells grow unrestrained in an organ or tissue in the body; can spread to tissues around it and destroy them or be transported through blood or lymph pathways to other parts of the body

  • Cancer staging is a method to determine how much a cancer has developed

  • Candidiasis is a yeast infection caused by the fungus Candida albicans; occurs most often in the vagina, but also in the mouth, on moist skin, or on the penis

  • Canker sore is small, painful sore that usually occurs on the inside of the lip or cheek, or sometimes under the tongue; caused by bacteria, irritation of the area, stress, or allergies

  • Capillary is a tiny blood vessel that connects the smallest arteries to the smallest veins and allows exchange of oxygen and other materials between blood cells and body tissue cells

  • Carbohydrate is a substance, mainly sugar and starch, that is a main source of energy for the body and is found in sources such as cereals, breads, pastas, grains, and vegetables

  • Carbon dioxide is a colorless, odorless gas present in small amounts in the atmosphere and formed during respiration

  • Carcinoma is a cancer that occurs on the surface or lining of an organ

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  • Cardiac arrest is the sudden cessation of the heart's pumping action, possibly due to a heart attack, respiratory arrest, electrical shock, extreme cold, blood loss, drug overdose, or a severe allergic reaction

  • Cardiogenic shock is a severely dangerous condition involving decreased blood output from the heart, usually as a result of a heart attack

  • Cardiomegaly is a condition marked by enlargement of the heart, either because of a thickened heart muscle or an enlarged heart chamber; usually a result of the heart having to work harder than normal, as occurs with high blood pressure

  • Cardiomyopathy is a disease of the heart muscle that results in decreased output and reduced blood flow

  • Cardiovascular system is the heart and blood vessels that are responsible for circulating blood throughout the body

  • Carotene is an orange pigment present in colored plants such as carrots that is converted by the body to the essential nutrient vitamin A

  • Carpal tunnel syndrome is a condition in which pressure on the median nerve in the wrist causes soreness, tingling, and numbness in the thumb and index and middle fingers

  • Cartilage is a connective tissue (softer than bone) that is part of the skeletal system, including the joints

  • Cast is a hard plaster or fiberglass shell that molds to a body part such as an arm and holds it in place for proper healing

  • Cataract is a disorder in which the lens of the eye becomes less transparent and in some cases a milky white, making vision less clear

  • Catheter is a hollow, flexible tube inserted into the body to put in or take out fluid, or to open up or close blood vessels

  • Catheterization is a technique in which a hollow, flexible tube is used to drain body fluids (such as urine), to introduce fluids into the body, or to examine or widen a narrowed vein or artery

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  • Cat-scratch fever is an illness transmitted to humans through a cat's bite or scratch, which is thought to be caused by an unidentified bacteria; characterized by a swollen lymph node or blister near the bite or scratch, fever, rash, and headache; most commonly occurring in children

  • Cauterization is the use of heat, an electric current, or a chemical to destroy tissue or stop bleeding

  • Cecum is the beginning of the large intestine, which is connected to the appendix at its lower end

  • Cell is the tiny structures that make up all the tissues of the body and carry out all of its functions

  • Cellulitis is a skin infection caused by bacteria (usually streptococci); can lead to tissue damage and blood poisoning if untreated; characterized by fever, chills, heat, tenderness, and redness

  • Cerebellum is a region of the brain located at the back; responsible for coordination of movement and maintaining balance

  • Cerebral palsy is a group of disorders of movement and posture resulting from damage to the brain early in a child's development; causes muscle weakness, difficulty coordinating voluntary movements, and sometimes complete loss of motion

  • Cerebrospinal fluid is a clear, watery fluid circulating in and around the brain and spinal column, which contains glucose, proteins, and salts for nutrition

  • Cerebrovascular disease is a disease affecting any artery supplying blood to the brain; may cause blockage or rupture of a blood vessel, leading to a stroke

  • Cerebrum is the largest part of the brain and the site of most of its activity, including sensory and motor functions

  • Cervical cap is a small rubber cup that is placed tightly over the cervix to prevent pregnancy

  • Cervical dysplasia is changes that occur in the cells on the surface of the cervix that usually precede the stages of cancer

  • Cervical incompetence is a weakness of the neck of the uterus, which can lead to spontaneous abortion due to an inability to support the weight of the fetus

  • Cervical smear is a procedure in which cells are scraped off of the cervix and examined to detect changes that might precede the stages of cancer; also called a Pap smear

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  • Cervix is a small, round organ making up the neck of the uterus and separating it from the vagina

  • Cesarean section is an operation performed to remove a fetus by cutting into the uterus, usually through the abdominal wall

  • Chancre is a painless sore that has a thick, rubbery base and a defined edge; usually occurs on the genitals after the contraction of the sexually transmitted disease syphilis

  • Chemotherapy is the treatment of infections or cancer with drugs that act on disease- producing organisms or cancerous tissue; may also affect normal cells

  • Chickenpox is a contagious disease that causes a rash and a fever; most commonly occurs during childhood

  • Chlamydia is microorganisms that cause several human infections and can be transmitted sexually

  • Cholera is a bacterial infection of the small intestine that causes severe watery diarrhea, dehydration, and possibly death

  • Cholesterol is a substance in body cells that plays a role in the production of hormones and bile salts and in the transport of fats in the bloodstream

  • Chondroma is a noncancerous tumor that occurs in cartilage

  • Chondrosarcoma is a cancerous cartilage tumor that develops inside of bone or on its surface

  • Chorionic villus sampling is a method of diagnosing fetal defects in which a small amount of tissue is taken from the placenta and analyzed for abnormalities

  • Choroiditis is inflammation of the blood vessels behind the retina that line the back of the eye

  • Chromosome analysis is examination of a person’s chromosomes either to determine if that person has an abnormality or to investigate one

  • Chronic is describes a disorder that continues for a long period of time

  • Cilia is tiny, hairlike structures on the outside of some cells, providing mobility

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  • Circumcision is the surgical removal of the foreskin of the penis

  • Claudication is a cramping pain in one or both legs while walking, which can cause limping

  • Claustrophobia is fear of being confined in an enclosed or crowded space

  • Clavicle is the medical term for the collarbone

  • Cleft lip is a birth defect in which the upper lip is split vertically, extending into one or both nostrils

  • Cleft palate is a birth defect in which the roof of the mouth is split, extending from behind the teeth to the nasal cavity; often occurs with other birth defects such as cleft lip and partial deafness

  • Clinical trial is carefully monitored and planned testing of a new drug or treatment

  • Clitoris is a small female organ located near the opening of the vagina that swells when sexually aroused

  • Clone is an exact copy of a gene, cell, or organism

  • Clotting factor is a substance in the blood that is needed for blood to harden and stop a wound from bleeding

  • Clubfoot is a genetic disorder in which the foot is twisted and misshapen

  • Cluster headache is severe pain that occurs suddenly and affects one side of the head, including the face and neck

  • CNS is see Central nervous system

  • Coagulation is a process that plays a large role in the hardening and thickening of blood to form a clot

  • Cocarcinogen is a substance that does not cause cancer by itself, but increases the effect of a substance that does cause cancer

  • Coccyx is four fused bones that form a triangular shape at the base of the spine (also known as the tailbone)

  • Cochlea is a coiled organ in the inner ear that plays a large role in hearing by picking up sound vibrations and transmitting them as electrical signals

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  • Cold sore is a small blister anywhere around the mouth that is caused by the herpes simplex virus

  • Colectomy is the complete or partial surgical removal of the large intestine (the colon), usually as treatment of a cancerous tumor or a narrowing and blockage of the intestine

  • Colic is waves of pain in the abdomen that increase in strength, disappear, and return; usually caused by a stone blocking a bile or urine passageway or an intestinal infection

  • Colitis is inflammation of the large intestine (the colon), which usually leads to abdominal pain, fever, and diarrhea with blood and mucus

  • Collapsed lung is a condition in which all or part of a lung cannot expand and fill with air

  • Colon is the main part of the large intestine, between the cecum and the rectum

  • Colonoscopy is investigation of the inside of the colon using a long, flexible fiberoptic tube

  • Color blindness is any vision disorder in which the person sees colors abnormally, has trouble distinguishing between them, or cannot see them at all

  • Colostomy is a surgical procedure in which some part of the colon is cut and moved to the surface of the abdomen so that feces can be passed into a bag worn outside of the body

  • Coma is a condition in which the area of the brain involved in maintaining consciousness is somehow affected, resulting in a state of unconsciousness in which the patient does not respond to stimulation

  • Common cold is an infection caused by a virus, which results in an inflamed lining of the nose and throat; characterized by a stuffy and runny nose and, sometimes, a sore throat

  • Computed tomography scanning is a technique for producing cross-sectional images of the body in which X-rays are passed through the body at different angles and analyzed by a computer; also called CT scanning or CAT scanning

  • Concussion is disturbance of electrical activity in the brain due to a blow to the head or neck, causing temporary loss of consciousness

  • Congenital is present or existing at the time of birth

  • Congestive heart failure is inability of the heart to efficiently pump blood through the body, causing buildup of blood in the veins and of other body fluids in tissue

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  • Conjunctiva is the clear membrane covering the white of the eye and the inside of the eyelid that produces a fluid that lubricates the cornea and eyelid

  • Conjunctivitis is inflammation of the conjunctiva; commonly called pinkeye

  • Constipation is difficult or infrequent bowel movements of hard, dry feces

  • Contraindication is an aspect of a patient's condition that makes the use of a certain drug or therapy an unwise or dangerous decision

  • Contusion is damage to the skin and underlying tissue as a result of a blunt injury; a bruise

  • Corn is a thickened callus on the foot that is caused by an improperly fitting shoe

  • Cornea is the clear, dome-shaped front portion of the eye’s outer covering

  • Coronary is describes structures that encircle another structure (such as the coronary arteries, which circle the heart); commonly used to refer to a coronary thrombosis or a heart attack

  • Coronary arteries is the arteries that branch off from the aorta and supply oxygen-rich blood to the heart muscle

  • Coronary artery bypass surgery is an operation in which a piece of vein or artery is used to bypass a blockage in a coronary artery; performed to prevent myocardial infarction and relieve angina pectoris

  • Corpuscle is a tiny, rounded structure in the body, such as a red or white blood cell

  • Corticosteroids is synthetic drugs that are used to replace natural hormones or to suppress the immune system and help prevent inflammation

  • CPR is see Cardiopulmonary resuscitation

  • Creatinine is a waste product that is filtered from the blood by the kidneys and expelled in urine

  • Croup is a usually mild and temporary condition common in children under the age of 4 in which the walls of the airways become inflamed and narrow, resulting in wheezing and coughing

  • Cruciate ligaments is two ligaments in the knee that cross each other and help stabilize the knee joint

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  • CT scanning is a procedure that uses X-rays and computers to create cross-sectional images of the body to diagnose and monitor disease

  • Culture is the artificial growth of cells, tissue, or microorganisms such as bacteria in a laboratory

  • Curettage is the use of a sharp, spoonlike instrument (a curet) to scrape away tissue that is abnormal or to obtain a sample that can be analyzed

  • CVS is see Chorionic villus sampling

  • Cyanosis is a bluish discoloration of the skin, caused by low levels of oxygen in the blood

  • Cyst is a lump filled with either fluid or soft material, occurring in any organ or tissue; may occur for a number of reasons but is usually harmless unless its presence disrupts organ or tissue function

  • Cystectomy is surgical removal of the bladder; the bladder is often replaced with a short length of small intestine

  • Cystic fibrosis is an inherited disorder in which the lungs are prone to infection, and fats and other nutrients cannot be absorbed into the body

  • Cystoscopy is examination of the urethra and bladder using a long, thin, fiberoptic tube

  • Cystostomy is the surgical placement of a drainage opening in the bladder

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  • D and C is see Dilatation and Curettage

  • Debridement is surgical removal of dead, damaged, or infected tissue, or some foreign material from a wound or burn

  • Decompression sickness is the formation of gas bubbles in the body’s tissues as a result of a scuba diver ascending too quickly from depth; commonly called the bends

  • Deep-vein thrombosis is the formation of a blood clot inside of a deep-lying vein, usually in the legs

  • Defecation is the passing of feces out of the body through the anus; a bowel movement

  • Defibrillation is a short electric shock to the chest to normalize an irregular heartbeat

  • Degenerative arthritis is the breakdown of the cartilage lining the bones in joints, usually weight-bearing joints (such as the knee); causes stiffness and pain (also called osteoarthritis)

  • Dehydration is excessive, dangerous loss of water from the body

  • Dementia is a gradual decline in mental ability usually caused by a brain disease, such as Alzheimer disease

  • Depot injection is injection of a drug into a muscle; the drug is designed to absorb slowly into the body

  • Depression is feelings of hopelessness, sadness, and a general disinterest in life, which for the most part have no cause and may be the result of a psychiatric illness

  • Dermabrasion is removal of the surface layer of skin with a sanding wheel to treat scarring or to remove tattoos

  • Dermis is the inner skin layer

  • Desensitization is the process of making a person less allergic to a substance by injecting gradually increasing amounts of the substance; sometimes done to prevent anaphylactic shock

  • Detoxification is treatment given either to fight a person's dependence on alcohol or other drugs or to rid the body of a poisonous substance and its effects

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  • Dextrocardia is a rare genetic condition in which the heart is located on the right side of the body, instead of the left

  • Dextrose is another name for the sugar glucose

  • Diabetes mellitus is a common form of diabetes in which the body cannot properly store or use glucose (sugar), the body's main source of energy

  • Dialysis is a procedure to treat kidney failure in which artificial means are used to filter waste, maintain acid-base balance, and remove excess fluid from the body

  • Diaper rash is a common condition in babies in which the skin in the diaper area becomes irritated and red, usually because of exposure to urine, feces, or heat

  • Diaphragm is the large, dome-shaped muscle separating the abdomen and chest that contracts and relaxes to make breathing possible; also, a thin, rubber dome that is used as a method of female contraception

  • Diastolic pressure is the blood pressure measured when the heart is at rest between beats

  • Diathermy is the use of high-frequency currents, microwaves, or ultrasound to produce heat in the body to increase blood flow, relieve pain, or destroy diseased tissue

  • Dilatation and Curettage is a procedure in which the vagina and cervix are widened and the lining of the uterus is scraped away to diagnose and treat disorders of the uterus

  • Diphtheria is a bacterial infection that causes a fever, headache, sore throat, and possibly death; diphtheria is rare in developed countries

  • Disk prolapse is a disorder in which one of the disks located between the vertebrae in the spine breaks down and the pulpy interior squeezes out, causing pressure on a nerve; commonly called a "slipped" or "ruptured" disk

  • Dislocation is displacement of the two bones in a joint

  • Distention is swelling, enlargement, or stretching

  • Diuretic is a drug that increases the amount of water in the urine, removing excess water from the body; used in treating high blood pressure and fluid retention

  • Diverticulitis is inflammation of diverticula (small sacs in the intestine's inner lining); can cause fever, pain, and tenderness

  • DNA is deoxyribonucleic acid; responsible for passing genetic information in nearly all organisms

  • Dominant gene is a gene that always produces its effect when it is present

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  • Dopamine is a chemical that transmits messages in the brain and plays a role in movement

  • Down syndrome is a genetic disorder in which a person’s cells have 1 too many chromosomes, causing moderate to severe mental handicap and a characteristic appearance

  • Duodenal ulcer is an erosion in the inner lining of the wall of the first part of the small intestine (called the duodenum)

  • Duodenum is the first part of the small intestine, immediately following the stomach

  • Dysentery is a severe intestinal infection, causing abdominal pain and diarrhea with blood or mucus

  • Dystrophy is any disorder in which cells become damaged or do not develop properly because they do not receive adequate nutrition

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  • Eardrum is a thin, oval-shaped membrane that separates the inner ear from the outer ear and is responsible for transmitting sound waves

  • ECG (sometimes called an EKG) is an electrocardiogram, which is a record of the electrical impulses that trigger the heartbeat; used to diagnose heart disorders

  • Echocardiogram is an image of the heart that is created by high-frequency (ultrasound) sound waves

  • Eclampsia is a serious condition that occurs in late pregnancy, characterized by seizures in the woman

  • Ectopic is occurring at an abnormal position or time

  • Eczema is inflammation of the skin, usually causing itchiness and sometimes blisters and scaling; may be caused by allergies, but often occurs for no apparent reason

  • Edema is abnormal buildup of fluid in the body, which may cause visible swelling

  • EEG is see Electroencephalography

  • Elective is describes a treatment or procedure that is not urgent and can be arranged at the patient’s convenience

  • Embolism is the blockage of a blood vessel by an embolus - something previously circulating in the blood (such as a blood clot, gas bubble, tissue, bacteria, bone marrow, cholesterol, fat, etc)

  • Embryo is a term used to describe a child in the womb from fertilization to 8 weeks following fertilization

  • Emetic is a substance that causes vomiting; used to treat some cases of poisoning and drug overdose

  • Emphysema is a chronic disease in which the small air sacs in the lungs (the alveoli) become damaged; characterized by difficulty breathing

  • Encephalitis is inflammation of the brain, usually caused by a virus; may be very mild and barely noticeable, but is usually serious and can progress from headache and fever to hallucinations, paralysis, and sometimes coma

  • Endarterectomy is surgery performed to remove the lining of an artery that has been narrowed by fatty tissue buildup

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  • Endemic is describes a disease that is always present in a certain population of people

  • Endocarditis is inflammation of the inner lining of the heart, usually the heart valves; typically caused by an infection

  • Endometrial polyp is a growth (usually noncancerous) occurring on the lining of the uterus

  • Endometriosis is a condition in which fragments of the endometrium are found in other pelvic organs

  • Endorphin is a group of chemicals produced in the brain that reduce pain and positively affect mood

  • Endoscope is a lighted instrument used to view the inside of a body cavity

  • Endothelium is the layer of flat cells that lines the blood and lymph vessels, the heart, and other structures in the body

  • Endotracheal tube is a plastic tube that is fed down into the trachea through the mouth or nose to supply oxygen to a person who is not breathing properly

  • Enteritis is inflammation of the small intestine, usually causing diarrhea

  • Enuresis is the medical term for wetting the bed

  • Enzyme is a chemical, originating in a cell, that regulates reactions in the body

  • Epidemic is a term used to describe a disease that is rare then suddenly affects more people than usually expected

  • Epididymis is a long, coiled tube, exiting from the back of the testicle, in which sperm mature

  • Epidural anesthesia is a method of pain relief in which a painkilling drug is injected into the space surrounding the spinal cord to block sensations in the abdomen and lower body

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  • Epilepsy is a disorder of the nervous system in which abnormal electrical activity in the brain causes seizures

  • Epinephrine is a hormone produced by the adrenal glands in response to stress, exercise, or fear; increases heart rate and opens airways to improve breathing; also called adrenaline

  • Episcleritis is a patch of inflammation on the outer layer of the white of the eye

  • Episiotomy is a surgical procedure in which an incision is made in the tissue between the vagina and anus to prevent tearing of this tissue during childbirth

  • Epithelium is the layer of cells that covers the body and lines many organs

  • Epstein-Barr virus is a virus that is the cause of mononucleosis and is involved in Burkitt’s lymphoma

  • Erysipelas is an infection caused by streptococci bacteria; characterized by fever and rash

  • Erythrocyte sedimentation rate is a measure of the time it takes for red blood cells to collect at the bottom of a sample of blood; an elevated rate may mean that there is inflammation somewhere in the body

  • Erythroplakia is red patches in the mucous membranes of the mouth, throat, or voice box (larynx) that can become cancerous; risk factors include smoking pipes and chewing tobacco

  • Esophageal spasm is irregular contractions of the muscles in the esophagus, which lead to difficulty swallowing

  • Esophageal varices is swollen veins in the lower esophagus and possibly the upper part of the stomach; can cause vomiting of blood and passing of black stool

  • Esophagus is a tube-shaped canal in the digestive tract, connecting the throat to the stomach

  • Estrogen is a group of hormones (produced mainly in the ovaries) that are necessary for female sexual development and reproductive functioning

  • Estrogen replacement therapy is treatment with synthetic estrogen drugs to relieve symptoms of menopause and to help protect women against osteoporosis and heart disease

  • Eustachian tube is the tube that connects the middle ear and the back of the nose, draining the middle ear and regulating air pressure

  • Euthanasia is painlessly ending the life of a patient with an incurable disease who requests to die

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  • Excision is the surgical removal of diseased tissue

  • Excretion is the process by which the body rids itself of waste

  • Exercise stress test is the monitoring of the heart during strenuous exercise, usually on a treadmill or exercise bicycle, to evaluate how the heart responds to stress

  • Exercise thallium test is an imaging test performed during and after an exercise stress test to evaluate functioning of the heart muscles

  • Exogenous is arising from outside of the body

  • Expectorant is a medication used to promote the coughing up of phlegm from the respiratory tract

  • External version is external repositioning of the fetus in the womb to the correct birth position

  • Extradural anesthesia is injection of an anesthetic into the space outside the dura mater, the fibrous membrane that envelops the spinal cord

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  • Facial palsy is inability to move the muscles of the face, usually on only one side, due to inflammation of a nerve

  • Failure to thrive is describes a baby who grows and gains weight slower than expected

  • Fallopian tube is either of two long, slender ducts connecting a woman's uterus to her ovaries, where eggs are transported from the ovaries to the uterus and sperm may fertilize an egg

  • Familial is a term describing a disorder or characteristic (such as male pattern baldness) that occurs within a family more often than would be expected

  • Fasciitis is inflammation of the layer of connective tissue that covers, separates, and supports muscles

  • Fatty acid is any of a number of carbon-, oxygen-, and hydrogen-containing molecules that make up fats

  • Febrile is a term used to describe something related to a fever, such as febrile seizures (seizures occurring in a child who has a fever)

  • Fecal occult blood test is a test that uses a piece of chemically sensitive paper to detect blood in a stool sample; used to screen for possible signs of cancer in the large intestine or rectum

  • Femur is the bone located between the hip and the knee; the thighbone

  • Fertility drug is a drug used to treat infertility that contains hormones or substances associated with hormones

  • Fertilization is the joining of an egg and a sperm, creating the first cell of a new life

  • Fetal alcohol syndrome is a combination of defects in a fetus as a result of the mother drinking alcohol during pregnancy

  • Fetal distress is physical distress experiencd by a fetus because of lack of oxygen

  • Fetal monitoring is the use of an instrument to record or listen to a fetus' heartbeat during pregnancy and labor

  • Fetal tissue transplant is an experimental procedure in which cells are taken from an aborted fetus and placed into the brain of a person with a brain disease such as Parkinson's

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  • Fetus is the term used to refer to an unborn child from 8 weeks after fertilization to birth

  • Fiber is a constituent of plants that cannot be digested, which helps maintain healthy functioning of the bowels

  • Fiberoptics is thin, flexible instruments that transmit light and images, allowing structures inside of the body to be viewed

  • Fibrillation is rapid, inefficient contraction of muscle fibers of the heart caused by disruption of nerve impulses

  • Fibroadenoma is a noncancerous tumor commonly found in the breast

  • Fibroid is a noncancerous tumor of the uterus made up of smooth muscle and connective tissue

  • Fibroma is a noncancerous tumor of connective tissue

  • Fibrosis is abnormal formation of connective or scar tissue

  • Fifth disease is a childhood infection caused by a virus, which often starts as a rash on the cheeks and spreads

  • Fissure is a groove or slit on the body or in an organ

  • Fistula is an abnormal passageway from one organ to another or from an organ to the body surface

  • Fitness is a measure of a person's physical strength, flexibility, and endurance

  • Flatulence is excessive air or gas in the intestines, which is expelled through the anus

  • Floaters is small spots that float across the field of vision, caused by debris floating in the gel-like substance that fills the eye

  • Flu is see Influenza

  • Fluke is a parasitic flatworm that can infest humans

  • Fluoride is a mineral that helps protect teeth against decay

  • Fluoroscopy is a method used to view organ structure and function by passing X-rays through the body and monitoring the resulting image on a fluorescent screen

  • Folic acid is a vitamin essential to the production of red blood cells; plays an important role in the growth a developing fetus

  • Follicle is a tiny pouchlike cavity in a structure of the body, such as a hair follicle

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  • Follicle stimulating hormone is a hormone produced by the pituitary gland in the brain that stimulates the testicles to produce sperm in males and causes eggs to mature in females

  • Folliculitis is the inflammation of hair follicles due to a bacterial infection, causing boils or tiny blisters containing pus

  • Fontanelles is the two soft spots on a baby’s scalp that are the result of gaps in the skull where bones have not yet fused

  • Food poisoning is stomach pain, diarrhea, and/or vomiting caused by eating contaminated food

  • Forceps is instruments resembling tweezers that are used to handle objects or tissue during surgery

  • Forceps delivery is the use of an instrument that cups the baby's head (called an obstetric forceps), to help deliver a baby

  • Foreign body is an object in an organ or body cavity that is not normally present

  • Foreskin is the loose skin that covers the head of the penis

  • Fraternal twins is twins that develop from two different eggs fertilized by two different sperm; are not identical

  • Frostbite is damage to body tissue as a result of freezing

  • FSH is see Follicle stimulating hormone

  • Fulminant is describes a disorder that begins suddenly and worsens quickly

  • Fungus is an organism that is dependent on another organism for nourishment

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  • Galactocele is a milk-filled tumor in a blocked breast milk duct

  • Galactorrhea is breast milk production by a woman who is not pregnant and has not just given birth

  • Galactose is a sugar that is formed from the breakdown of lactose

  • Galactosemia is a genetic disorder in which galactose cannot be converted into glucose

  • Gallbladder is a small, pear-shaped sac positioned under the liver, which concentrates and stores bile

  • Gallstone is a round, hard mass of cholesterol, bile, or calcium salts that is found in the gallbladder or a bile duct

  • Gallstone ileus is an abnormal condition in which a gallstone passes from the gallbladder into the intestines through an abnormal passage and blocks the intestine

  • Gamete intrafallopian transfer is a method of treating infertility in which eggs are taken from a woman's ovaries and fertilized with sperm and then the fertilized egg is injected into one of her fallopian tubes

  • Gamma globulin is a substance prepared from blood that carries antibodies to most common infections; also used in immunizations

  • Ganglion is a fluid-filled cyst attached to a tendon sheath or joint

  • Gangrene is death of a tissue because of a lack of blood supply

  • Gastrectomy is surgical removal of all or part of the stomach

  • Gastric juice is digestive fluids produced by the lining of the stomach that break down proteins and destroy harmful organisms

  • Gastric lavage is washing out of the stomach with water, often to treat poisoning; commonly called "stomach pumping"

  • Gastrin is a hormone that stimulates the release of gastric acid in the stomach

  • Gastrinoma is a tumor that produces gastrin, making the stomach and duodenum more acidic

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  • Gastritis is inflammation of the mucous membrane lining of the stomach; can have a number of causes, including viruses, bacteria, and use of alcohol and other drugs

  • Gastrointestinal series is a set of X-rays, taken at different intervals after a barium sulfate solution is swallowed, to examine the gastrointestinal tract

  • Gastrointestinal tract is the part of the digestive system that includes the mouth, esophagus, stomach, and intestines

  • Gastroscopy is examination of the esophagus, stomach, and the first part of the small intestine (duodenum) using an endoscope inserted through the mouth

  • Gastrostomy is the surgical creation of an opening in the abdominal wall into the stomach for drainage or a feeding tube

  • Gaucher’s disease is a genetic disorder in which lipids cannot be properly broken down and build up in certain cells; causes enlargement of the spleen and liver, bone damage, and anemia

  • Gavage is an artificial feeding technique in which liquids are passed into the stomach by way of a tube inserted through the nose

  • Gene is the basic unit of DNA, which is responsible for passing genetic information; each gene contains the instructions for the production of a certain protein

  • General anesthesia is a method of preventing pain in which the patient is induced to lose consciousness

  • Generic drug is a drug marketed under its chemical name, instead of a brand name

  • Gene therapy is an experimental procedure in which disease-causing genes are replaced by normal, healthy genes

  • Genetic analysis is examination of DNA in a laboratory to diagnose genetic disorders

  • Genetic counseling is information and advice given to persons considering pregnancy about the risk that a child will have an inheritable birth defect or genetic disorder

  • Genetic disorder is a disorder caused partly or completely by a defect in genes, which carry hereditary information

  • Genetic engineering is the alteration of genetic information to change an organism; mainly used to produce vaccines and drugs such as insulin

  • Genital herpes is an infection caused by the herpes simplex virus, which causes a painful rash of fluid-filled blisters on the genitals; transmitted through sexual contact

  • Genital tract is the organs that make up the reproductive system

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  • Genital wart is a growth on the skin in or around the vagina, penis, or anus, transmitted by sexual contact; can cause cancer of the cervix

  • Genome is the complete set of an organism’s genes

  • Geographic tongue is a condition in which the tongue is patchy where surface cells break down

  • Germ cell is a sperm or egg cell, or the immature form of either

  • Gestation is the period of time between fertilization of an egg by a sperm and birth of a baby

  • Giardiasis is infection with a single-celled parasite, causing abdominal cramps, diarrhea, and nausea

  • GIFT is see Gamete intrafallopian transfer

  • Gingivectomy is surgical removal of a diseased part of the gums

  • Gingivitis is inflammation of the gums, typically caused by a buildup of plaque due to poor hygiene

  • Gland is a group of cells or an organ that produces substances (such as hormones and enzyme) that are used by the body

  • Glaucoma is a disease in which eye damage is caused by an increase in the pressure of the fluid within the eye

  • Glioma is a brain tumor arising from cells that support nerve cells

  • Glomerulonephritis is inflammation of the filtering structures in the kidneys, hindering removal of waste products from the blood

  • Glossectomy is surgical removal of all or part of the tongue

  • Glucagon is a hormone produced by the pancreas that converts stored carbohydrates (glycogen) into glucose, the body’s energy source

  • Glucose is a sugar that is the main source of energy for the body

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  • Glucose tolerance test is a test that evaluates the body's response to glucose after a period of fasting; used to check for diabetes mellitus

  • Glycogen is the main form that glucose, the body’s energy source, takes when it is stored

  • Goiter is enlargement of the thyroid gland, which produces a swelling on the neck

  • Gonorrhea is a common sexually transmitted disease, characterized by painful urination or a discharge from the penis or vagina

  • Gout is a disorder marked by high levels of uric acid in the blood; usually experienced as arthritis in one joint

  • Graft is healthy tissue that is used to replace diseased or defective tissue

  • Grand mal is a type of seizure occurring with epilepsy, producing loss of consciousness and involuntary jerking movements

  • Granuloma is a mass of tissue that forms at a site of inflammation, injury, or infection as a part of the healing process

  • Graves' disease is an autoimmune disease that causes goiter, overproduction of thyroid hormones, and sometimes bulging eyeballs

  • Guillain-Barré syndrome is a peripheral nervous system disease in which nerve inflammation causes weakness, loss of movement, and loss of sensation in the arms and legs

  • Guthrie test is a blood test performed on babies to test for phenylketonuria

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  • Hair follicle is a tiny opening in the skin from which a hair grows

  • Halitosis is the clinical term for bad breath; commonly caused by poor oral hygiene or eating certain foods; if persistent it can be a sign of illness

  • Hallucination is a perception that occurs when there is actually nothing there to cause it (such as hearing voices when there are none)

  • Hammer toe is an abnormality in the tendons of the toe that causes the toe to be flexed at all times

  • Hamstring muscle is a muscle located at the back of the thigh that bends the leg at the knee and moves the leg backward

  • Hashimoto’s disease is a disease in which the body’s immune system attacks cells of the thyroid gland, resulting in a decrease in thyroid hormones

  • Hay fever is the common name for allergic rhinitis

  • HDL is see High-density lipoprotein

  • Heart block is a disorder of the heart caused by a blockage of the nerve impulses to the heart that regulate heartbeat; may lead to dizziness, fainting, or stroke

  • Heartburn is a burning sensation experienced in the center of the chest up to the throat; may be caused by overeating, eating spicy food, or drinking alcohol; recurrent heartburn may be caused by acid reflux

  • Heart failure is the inability of the heart to pump blood effectively

  • Heart-lung machine is a machine that takes over the functions of the heart and lungs during certain types of surgery

  • Heart rate is the rate at which the heart pumps blood, measured in the number of heartbeats per minute

  • Heart valve is the structure at each exit of the four chambers of the heart that allows blood to exit but not to flow back in

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  • Heat exhaustion is fatigue, dizziness, and nausea experienced because of overexposure to heat; if not treated it can result in heat stroke

  • Heat stroke is a life-threatening condition resulting from extreme overexposure to heat, which disrupts the body's system of regulating temperature

  • Heel spur is an abnormal, often painful outgrowth of bone on the back of the heel

  • Heimlich maneuver is a first-aid technique for choking; dislodges an object that is blocking a person’s airway

  • Helper T cells is white blood cells, responsible for regulating other cells in the body's immune system, that are the main targets of the AIDS virus; also called CD4 cells

  • Hemangioma is a purple-red mark on the skin, caused by an excess of blood vessels

  • Hematocrit is the percentage of total blood volume that consists of red blood cells, which is determined by laboratory testing; can be an indicator of disease or injury

  • Hematoma is an accumulation of blood from a broken blood vessel

  • Hematuria is blood in the urine, which can be caused by urinary tract disorders (such as cysts, tumor, or stones) or by an infection

  • Hemochromatosis is a genetic disorder in which too much iron is absorbed from food

  • Hemodialysis is a method used to treat kidney failure, in which blood is passed through a machine that purifies it and returns it to the body

  • Hemoglobin is the pigment in red blood cells that is responsible for carrying oxygen; hemoglobin bound to oxygen gives blood its red color

  • Hemolysis is the breakdown of red blood cells in the spleen, which is normal but can cause jaundice and anemia when the red blood cells are broken down too quickly

  • Hemophilia is an inherited disorder in which a person's blood lacks a certain protein important in forming blood clots, leading to excessive bleeding

  • Hemorrhoid is a bulging vein either at the opening of the anus or just inside the anus, often caused by childbirth or straining during bowel movements

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  • Hemostasis is the stopping of bleeding by the body’s mechanisms

  • Hemothorax is an accumulation of blood between the chest wall and the lungs

  • Hepatectomy is surgical removal of all or part of the liver

  • Hepatic is a term used to describe something that is related to the liver

  • Hepatitis is inflammation of the liver, which may be caused by a viral infection, poisons, or the use of alcohol or other drugs

  • Hepatitis A is a form of hepatitis caused by the hepatitis A virus, usually transmitted by contact with contaminated food or water

  • Hepatitis B is a form of hepatitis (generally more serious than hepatitis A) caused by the hepatitis B virus, which is transmitted through sexual contact or contact with infected blood or body fluids

  • Hepatitis C is a form of hepatitis caused by the hepatitis C virus, which is transmitted through sexual contact or contact with infected blood or body fluids

  • Hepatitis D is a form of hepatitis that only causes symptoms when the individual is already infected with hepatitis B

  • Hepatoma is a cancerous tumor of the liver

  • Hereditary is describes a genetic trait that is passed from parents to children

  • Hereditary spherocytosis is a genetic disorder in which red blood cells are smaller, rounder, and more fragile than normal, causing hemolytic anemia

  • Hermaphroditism is a rare condition in which an individual is born with both male and female reproductive organs

  • Hernia is the bulging of an organ or tissue through a weakened area in the muscle wall

  • Herpes encephalitis is brain inflammation caused by a herpes simplex virus that has spread from another part of the body

  • Herpes simplex is infection by the herpes simplex virus, which causes blisterlike sores on the face, lips, mouth, or genitals; in rare cases, can also affect the eyes, fingers, or brain

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  • Hiatal hernia is a type of hernia in which the stomach bulges up into the chest cavity through an opening in the diaphragm

  • Hiccup is involuntary sudden contraction of the diaphragm along with the closing of the vocal cords, producing a "hiccup" sound

  • High-density lipoprotein is a type of protein found in the blood that removes cholesterol from tissues, protecting against heart disease

  • Hirschsprung's disease is a condition that is present at birth in which nerve cells do not develop in parts of the intestine, causing the intestine to narrow and block the passage of feces

  • Hirsutism is excessive hair or hair growth in unusual places, especially in women

  • Histamine is a chemical in some cells of the body that is released during allergic reactions, causing inflammation; also causes production of acid in the stomach and narrowing of the airways

  • H2 (histamine) blocker is a drug used in the treatment of peptic ulcers that blocks histamine from causing acid production in the stomach

  • Histoplasmosis is a respiratory disease acquired by inhaling the spores of a fungus found in soil, especially where there are bird or bat droppings

  • HIV is see Human immunodeficiency virus

  • Hives is the common term for urticaria, an itchy, inflamed rash that results from an allergic reaction

  • Hodgkin's disease is a cancer of lymphoid tissue (found in lymph nodes and the spleen) that causes the lymph nodes to enlarge and function improperly; may cause illness, fever, loss of appetite, and weight loss

  • Homeostasis is the body's coordinated maintenance of the stable, internal environment by regulating blood pressure, blood sugar, body temperature, etc

  • Homocystinuria is a genetic disorder in which an enzyme deficiency causes a substance called homocystine to build up in the blood, leading to mental handicap and skeletal abnormalities

  • Homosexuality is being sexually attracted to members of the same sex

  • Hookworm is infestation by a small, round, blood-sucking parasite; commonly causes a rash on the foot, but can also cause cough, pneumonia, and anemia

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  • Hormonal implant is surgical insertion of a small object just under the skin that slowly releases a synthetic hormone for purposes such as birth control

  • Hormone is a chemical produced by a gland or tissue that is released into the bloodstream; controls body functions such as growth and sexual development

  • Hospice is a hospital or an area of a hospital dedicated to treating people who are dying, often of a specific cause

  • Hot flash is a sudden, temporary feeling of heat and sometimes sweating; usually occurs as a result of low estrogen levels in women because of menopause or after a hysterectomy

  • HTLV is see Human T-cell lymphotrophic virus

  • Human immunodeficiency virus is a retrovirus that attacks helper T cells of the immune system and causes acquired immunodeficiency syndrome (AIDS); transmitted through sexual intercourse or contact with infected blood

  • Human T-cell lymphotrophic virus is a virus similar to HIV that affects the same helper T cells, but usually accompanies adult T-cell leukemia or T-cell lymphomas

  • Hydramnios is an excess of amniotic fluid in the uterus during pregnancy

  • Hydrocele is a painless swelling of the scrotum, caused by a collection of fluid around the testicle; commonly occurs in middle aged men

  • Hydrocephalus is excess cerebrospinal fluid within the brain; commonly referred to as "water on the brain"

  • Hydrocortisone is a corticosteroid drug that is used to treat inflammation and allergies

  • Hygiene is the practice, maintenance, and study of health; commonly refers to cleanliness

  • Hymen is a thin fold of membrane partly closing the opening of the vagina; usually torn during first sexual intercourse or insertion of a tampon

  • Hyperactivity is a type of behavior characterized by excessive physical activity, sometimes associated with neurological or psychological causes

  • Hyperalimentation is a method of providing nutrients by the use of a tube or intravenously to a person who cannot eat food or needs nutrients because of an illness

  • Hyperbilirubinemia is a condition in which there is too much bilirubin, a substance produced when red blood cells are broken down; can lead to jaundice

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  • Hypercalcemia is a condition marked by abnormally high levels of calcium in the blood; can lead to disturbance of cell function in the nerves and muscles and, if not treated, can be fatal

  • Hypercholesterolemia is an abnormally high level of cholesterol in the blood, which can be the result of an inherited disorder or a diet that is high in fat

  • Hyperglycemia is a condition characterized by abnormally high levels of glucose in the blood, usually as a result of untreated or improperly controlled diabetes mellitus

  • Hyperlipidemia is a general term for a group of disorders in which lipid levels in the blood are abnormally high, including hypercholesterolemia

  • Hyperparathyroidism is overactivity of the parathyroid glands, which increases calcium levels in the blood (called hypercalcemia) and decreases calcium in bones (causing osteoporosis)

  • Hypersensitivity is an excessive response of the body’s immune system to a foreign protein

  • Hypertension is abnormally high blood pressure, even when at rest

  • Hyperthyroidism is overactivity of the thyroid gland, causing nervousness, weight loss, fatigue, and diarrhea

  • Hypertrophy is increase in the size of an organ due to an increase in the size of its cells

  • Hypochondriasis is an abnormal condition in which a person is overly concerned with health and believes that he or she is suffering from a major illness despite medical opinion to the contrary

  • Hypodermic needle is a thin, hollow needle attached to a syringe; used to inject a medication under the skin, into a vein, or into a muscle

  • Hypoglycemia is abnormally low levels of glucose in the blood

  • Hypoplasia is failure of a tissue or organ to develop normally

  • Hypotension is the medical term for abnormally low blood pressure, which results in reduced blood flow to the brain, causing dizziness and fainting

  • Hypothyroidism is underactivity of the thyroid gland, causing tiredness, cramps, a slowed heart rate, and possibly weight gain

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  • Hypoxemia is a reduced level of oxygen in the blood

  • Hypoxia is a reduced level of oxygen in tissues

  • Hysteria is a term used to describe symptoms that are caused by mental stress and occur in someone who does not have a mental disorder

  • Hysterosalpingography is an X-ray examination performed to examine the inside of the uterus and fallopian tubes, in order to investigate and possibly treat infertility

  • Hysteroscopy is a method used to examine the inside of the uterus and the cervix using a viewing instrument

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  • Iatrogenic is a term used to describe a disease, disorder, or medical condition that is a direct result of medical treatment

  • Ichthyosis is a variety of diseases in which the skin is dry and scaly

  • Idiopathic is a term used to describe something that occurs of an unknown cause

  • Ileostomy is a surgical procedure in which the lower part of the small intestine (the ileum) is cut and brought to an opening in the abdominal wall, where feces can be passed out of the body

  • Ileum is the lowest section of the small intestine, which attaches to the large intestine

  • Ilium is one of the two bones that form the hip on either side of the body

  • Imaging is the technique of creating pictures of structures inside of the body using X-rays, ultrasound waves, or magnetic fields

  • Immune deficiency is impairment of the immune system, which reduces protection against infection and illness

  • Immune system is the cells, substances, and structures in the body that protect against infection and illness

  • Immunity is resistance to a specific disease because of the responses of the immune system

  • Immunization is the process of causing immunity by injecting antibodies or provoking the body to make its own antibodies against a certain microorganism

  • Immunoglobin is proteins in blood and tissue fluids that help destroy microorganisms such as bacteria and viruses

  • Immunology is the study of the immune system, including how it functions and disorders that affect it

  • Immunostimulant is a drug that increases the ability of the body’s immune system to fight disease

  • Immunosuppressant is a drug that inhibits the activity of the immune system; used to prevent rejection of a transplant organ and in disorders where the body's immune system attacks its own tissues

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  • Impacted fracture is a bone break in which the two broken ends have been forced into each other

  • Imperforate anus is a birth defect in which the opening of the anus is not formed normally

  • Impetigo is a highly contagious skin infection caused by bacteria, usually occurring around the nose and mouth; commonly occurring in children

  • Implant is an organ, tissue, or device surgically inserted and left in the body

  • Impotence is the inability to acquire or maintain an erection of the penis

  • Incompetent cervix is an abnormally weak cervix, which widens prematurely during pregnancy as a result of the weight of a developing fetus; may result in a miscarriage

  • Incontinence is inability to hold urine or feces inside of the body

  • Incubation period is the time period between when an infectious organism enters the body and when symptoms occur

  • Indigestion is uncomfortable symptoms brought on by overeating or eating spicy, rich, or fatty foods; characterized by heartburn, pain in the abdomen, nausea, and gas, and can be more serious if recurrent

  • Infarction is tissue death due to lack of blood supply

  • Infection is disease-causing microorganisms that enter the body, multiply, and damage cells or release toxins

  • Infective arthritis is arthritis caused by bacteria from a wound or the bloodstream entering a joint

  • Infertility is the inability to have children as a result of sexual intercourse

  • Inflammation is redness, pain, and swelling in an injured or infected tissue produced as a result of the body's healing response

  • Inflammatory bowel disease is the general term for two inflammatory disorders affecting the intestines; also known as Crohn's disease and ulcerative colitis

  • Influenza is a viral infection characterized by headaches, muscle aches, fever, weakness, and cough; commonly called the "flu"

  • Informed consent is agreement to undergo a medical procedure after the technique, its risks, and its possible complications have been explained

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  • Infusion is the introduction of a substance, such as a drug or nutrient, into the bloodstream or a body cavity

  • Ingestion is taking something into the body through the mouth

  • Ingrown toenail is a painful condition of the big toe in which the nail grows into the skin on either side, causing inflammation and/or infection

  • Inguinal hernia is the bulging of a portion of the intestines or abdominal tissue into the muscles of the groin (the area just below the abdomen)

  • Inhaler is a device used to introduce a powdered or misted drug into the lungs through the mouth, usually to treat respiratory disorders such as asthma

  • Inheritance is the passing of traits from parent to child through genes

  • Injection is the use of a syringe and needle to insert a drug into a vein, muscle, or joint or under the skin

  • Insemination is the placement of semen into a woman's uterus, cervix, or vagina

  • In situ is "in place"; often describes a cancer that has not spread

  • Insomnia is difficulty falling or remaining asleep

  • Insulin is a hormone made in the pancreas that plays an important role in the absorption of glucose (the body's main source of energy) into muscle cells

  • Insulinoma is a noncancerous tumor of the insulin-producing cells of the pancreas; the tumor releases excess insulin into the blood, causing glucose levels to drop dangerously low

  • Interferon is a protein produced by body cells that fights viral infections and certain cancers

  • Internal fixation is a method of holding a broken bone in place using surgically inserted screws, rods, or plates

  • Interstitial is lying between body structures or in the interspaces of tissues

  • Interstitial lung disease is a disease of the connective tissue surrounding the air sacs of the lungs that causes a dry cough, scarring of lung tissue, and shortness of breath

  • Interstitial radiation therapy is a treatment for cancer in which a radioactive material is inserted into or near a tumor to provide direct radiation

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  • Intervertebral disks is broad, flat cartilage structures containing a gel-like fluid that cushion and separate vertebrae

  • Intestinal bypass is a surgical procedure in which the beginning of the large intestine is joined to its end so that less food is absorbed; because of serious side effects, usually performed only on seriously obese people

  • Intestine is a long, tube-shaped organ that extends from the stomach to the anus; absorbs food and water and passes the waste products of digestion as feces

  • Intra-aortic balloon pump is a small balloon inserted into the aorta that helps to circulate blood by inflating between heartbeats

  • Intractable is describes a condition that does not respond to treatment

  • Intramedullary rod is a strong metal rod that is placed inside of a broken bone to help it heal correctly

  • Intrinsic is a term used to describe something originating from or located in a tissue or organ

  • Intubation is the passage of a tube into an organ or body structure; commonly used to refer to the passage of a tube down the windpipe for artificial respiration

  • Invasive is describes something that spreads throughout body tissues, such as a tumor or microorganism; also describes a medical procedure in which body tissues are penetrated

  • In vitro is "in glass"; a biological test or process that is carried out in a laboratory

  • In vitro fertilization is a treatment for infertility in which an egg and a sperm are joined outside the woman's body, and the fertilized egg is then inserted into the uterus or fallopian tube

  • In vivo is "in the living body"; a biological process that occurs inside of the body

  • Involuntary is occurring without a person’s control or participation

  • Iodine is an element for the formation of thyroid hormones

  • Ionizing radiation is radiation that damages cells or genes; can be used to treat cancer

  • IQ is intelligence quotient; a measure of a person's intelligence as determined by specific tests

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  • Iris is the colored part of the eye

  • Iron is a mineral necessary for the formation of important biological substances such as hemoglobin, myoglobin, and certain enzymes

  • Iron-deficiency anemia is a type of anemia caused by a greater-than-normal loss of iron due to bleeding, problems absorbing iron, or a lack of iron in the diet

  • Irrigation is the cleansing of a wound by flushing it with water, a medicated solution, or some other fluid

  • Irritable bladder is involuntary contractions of muscles in the bladder, which can cause lack of control of urination

  • Irritable bowel syndrome is abnormal muscle movement in the intestines, which causes abdominal pain and irregular bowel movements (diarrhea, constipation, or both)

  • Ischemia is a condition in which a tissue or organ does not receive a sufficient supply of blood

  • IUD is see Intrauterine device

  • IVF is see In vitro fertilization

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  • Jaundice is yellowing of the skin and whites of the eyes because of the presence of excess bilirubin in the blood; usually a sign of a disorder of the liver

  • Jock itch is an infection in the groin area caused by a fungus

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  • Kaposi's sarcoma is a skin cancer that is characterized by purple-red tumors that start at the feet and spread upward on the body; commonly occurs in people who have AIDS

  • Kawasaki disease is a childhood disease causing fever, rash, skin peeling, swollen lymph nodes, and possibly complications of the heart and brain

  • Keloid is a raised, firm, thick scar that forms as a result of a defect in the natural healing process

  • Keratin is a tough protein found in skin, nails, and hair

  • Keratolytic is drugs that remove the keratin-containing outer layer of skin; used to treat skin disorders such as warts and dandruff

  • Keratoplasty is surgical replacement or reshaping of the cornea

  • Keratosis is a growth on the skin that is the result of overproduction of the protein keratin

  • Ketoacidosis is the dangerous accumulation of chemicals called ketones in the blood, sometimes occurring as a complication of diabetes mellitus; also called ketosis

  • Kidney is one of two organs that are part of the urinary tract; responsible for filtering the blood and removing waste products and excess water as urine

  • Kidney stone is a hard mass composed of substances from the urine that form in the kidneys

  • Killer T cells is white blood cells that are part of the immune system and destroy microorganisms and cancer cells

  • Kilocalorie is a unit of energy; equal to a nutritional calorie

  • Kimmelstiel-Wilson syndrome is a kidney disorder that can occur as a complication of diabetes mellitus; can cause swelling, high blood pressure, and kidney failure

  • Klinefelter’s syndrome is a genetic disorder in which a man has at least 1 extra X chromosome in his cells, causing infertility and female characteristics

  • Knee-jerk reflex is a test for a reflexive extension of the leg to check the functioning of the nervous system; tapping the knee just below the kneecap should cause the lower part of the leg to jerk upward

  • Kyphosis is excessive curvature of the spine, which usually affects the top part of the spine and causes a hump

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  • Labia is the two pairs of skinfolds that protect the opening of the vagina

  • Labor is the interval from onset of contractions to birth of a baby

  • Labyrinthitis is inflammation of the fluid-containing chamber of the inner ear (called the labyrinth) that maintains balance; can cause a feeling that one's surroundings are spinning around (known as vertigo)

  • Lactase deficiency is an inherited disorder in which a person does not have the enzyme lactase, which breaks down lactose (the sugar found in dairy products); lactase deficiency leads to lactose intolerance, which means the inability to digest lactose

  • Lactation is the production of breast milk after giving birth

  • Lactation suppression is a decrease in milk production during pregnancy as a result of high levels of estrogen in the blood

  • Lactic acid is an acid produced by glucose-burning cells when these cells have an insufficient supply of oxygen

  • Lactose is the sugar found in dairy products

  • Lamaze method is a method of preparing for childbirth that stresses physical conditioning, relaxation, and breathing exercises

  • Laminectomy is a surgical procedure that removes part of a vertebra to relieve pressure on the spinal cord or a nerve branching from the spinal cord

  • Laparoscope is a viewing instrument used to examine and treat disorders in the abdominal cavity; consists of a long tube with an eyepiece, a lens, and often a camera, which allows the image to be viewed on a monitor

  • Laparoscopy is a procedure done to examine the abdominal cavity using a laparoscope, usually to investigate pelvic pain or gynecologic conditions such as infertility

  • Large intestine is the part of the digestive tract that is located between the small intestine and the anus

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  • Laryngectomy is surgical removal of all or part of the voice box (larynx) as a treatment for cancer

  • Laryngitis is inflammation of the voice box, usually caused by a viral infection; characterized by a hoarse voice

  • Larynx is the medical term for the voice box, the organ in the throat that produces voice and also prevents food from entering the airway

  • Laser treatment is the use of a laser (a concentrated beam of light) to perform medical procedures, such as the destruction of tumors

  • Latent infection is an infection that lies dormant in the body for months or years but can reappear

  • Laxatives is drugs used to clear feces from the intestines; commonly used to treat constipation

  • Lazy eye is the common name for the visual defect resulting from untreated strabismus, in which the eyes are not correctly aligned

  • LDL is see Low-density lipoprotein

  • Lead poisoning is damage to the brain, nerves, red blood cells, or digestive system because of ingestion of lead

  • Learning disability is any of a variety of disorders, including hyperactivity, dyslexia, and hearing problems, that can interfere with a person's ability to learn

  • Leiomyoma is a noncancerous tumor of smooth muscle

  • Leishmaniasis is a group of parasitic diseases affecting the skin, mucous membranes, and internal organs; transmitted by the bite of a sandfly

  • Leptospirosis is infection by a spiral-shaped bacterium that affects the skin, eyes, muscles, kidneys, and liver; leptospirosis is carried by rodents

  • Lesch-Nyhan syndrome is a genetic disorder affecting only men that causes mental handicap, self-mutilation, and aggressive behavior

  • Lesion is an abnormality of structure or function in the body

  • Leukemia is a group of bone marrow cancers in which white blood cells divide uncontrollably, affecting the production of normal white blood cells, red blood cells, and platelets

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  • Leukocyte is another name for a white blood cells

  • Leukocyte count is the number of white blood cells in the blood, which is used as a measure of health and possible infection

  • Leukodystrophy is a group of childhood genetic disorders in which the protective coverings of the nerves are destroyed

  • Leukoplakia is white patches that can develop in the mouth or on the penis or the opening of the vagina and are potentially cancerous

  • LH is see Luteinizing hormone

  • Lichen planus is a common skin disease in which itchy, small, pink or purple spots appear on the arms or legs

  • Ligament is a tough, elastic band of tissue that connects bones and suupports organs

  • Ligation is the process of closing a blood vessel or duct by tying it off

  • Lipid-lowering drugs is drugs taken to lower the levels of specific fats called lipids in the blood in order to reduce the risk of narrowing of the arteries

  • Lipidosis is any disorder in which fats cannot be properly broken down by the digestive system

  • Lipids is a group of fats stored in the body and used for energy

  • Lipoma is a noncancerous tumor of fatty tissue

  • Lipoproteins is substances containing lipids and proteins, comprising most fats in the blood

  • Liposuction is a surgical procedure in which fat is removed from areas of the body using a suction pump

  • Listeriosis is a rare bacterial infection acquired by eating undercooked infected meat or from infected live animals; can be dangerous to newborns and the elderly

  • Lithotripsy is a procedure done to break up stones in the urinary tract using ultrasonic shock waves, so that the fragments can be easily passed from the body

  • Liver is the largest organ in the body, producing many essential chemicals and regulating the levels of most vital substances in the blood

  • Liver failure is the final stage of liver disease, in which liver function becomes so impaired that other areas of the body are affected, most commonly the brain

  • Lobe is a well-defined, separate part of an organ

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  • Local anesthesia is a method of preventing pain by inducing the loss of sensation in a certain area of the body while the patient remains awake

  • Locked joint is a joint that cannot be moved because of a disease or a lodged piece of bone or cartilage

  • Lockjaw is a spasm of the jaw muscles that prevents the mouth from opening, such as that caused by tetanus

  • Locomotor system is the structures of the body that are responsible for its movement

  • Lordosis is the inward curvature of the spine at the lower back, which is normal to a certain degree; abnormal as a result of certain medical conditions, being overweight, or having muscle problems

  • Low-density lipoprotein is a type of lipoprotein that is the major carrier of cholesterol in the blood, with high levels associated with narrowing of the arteries and heart disease

  • Lumbago is dull, aching pain in the lower back

  • Lumbar puncture is a procedure in which a needle is inserted into the lower region of the spinal canal to take out a sample of spinal fluid or to inject a drug

  • Lumbar spine is the lower part of the spine between the lowest pair of ribs and the pelvis; made up of five vertebrae

  • Lumpectomy is surgical removal of a section of breast containing cancer

  • Lung collapse is a condition in which all or part of a lung cannot expand and fill with air

  • Lungs is two organs in the chest that take in oxygen from the air and release carbon dioxide

  • Lupus erythematosus is a disorder of the immune system that causes inflammation of connective tissue

  • Luteinizing hormone is a hormone produced by the pituitary gland that causes the ovaries and testicles to release sex hormones and plays a role in the development of eggs and sperm

  • Lyme disease is a disease caused by bacteria transmitted through the bite of a tick; characterized by fever, rash, and inflammation of the heart and joints

  • Lymph is a milky fluid containing white blood cells, proteins, and fats; plays an important role in absorbing fats from the intestine and in the functioning of the immune system

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  • Lymphangiography is an X-ray procedure that creates images of the lymphatic system

  • Lymph node is a small gland that is part of the immune system; contains white blood cells and antibodies and helps fight against the spread of infection

  • Lymphocyte is a white blood cell that is an important part of the body's immune system, helping to destroy invading microorganisms

  • Lymphocytic leukemia is a disease in which white blood cells called lymphocytes divide uncontrollably

  • Lymphomas is a group of cancer of the lymph nodes and spleen that can spread to other parts of the body

  • Lymphosarcoma is another name for a non-Hodgkin's sarcoma; a cancerous tumor in lymphoid tissue

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  • Macula is the area of the retina that allows fine details to be observed at the center of vision; also refers to any small, flat spot on the skin

  • Magnesium is a mineral that is essential for many body functions, including nerve impulse transmission, formation of bones and teeth, and muscle contraction

  • Magnetic resonance imaging (MRI) is a technique that uses magnetic fields and radio waves to create high-quality cross-sectional images of the body without using radiation

  • Malabsorption is an impaired ability of the lining of the small intestine to absorb nutrients from food

  • Malaria is a parasitic disease spread by mosquitos that causes chills and fever; potentially fatal complications in the liver, kidneys, blood, and brain are possible

  • Malignant is a word used to describe a condition that is characterized by uncontrolled growth and/or that can be fatal, such as a cancerous tumor

  • Malignant hyperthermia is a reaction to certain anesthesia gases involving intense muscle contractions and a high fever

  • Malignant melanoma is the most serious type of skin cancer, in which a mole changes shape, darkens, becomes painful, and/or bleeds easily

  • Mallory-Weiss syndrome is a condition associated with alcoholism in which the lower end of the esophagus tears, causing vomiting of blood

  • Mammography is an X-ray procedure done to detect breast cancer

  • Mammoplasty is a general term for a cosmetic operation on the breasts; includes breast reduction, enlargement, and reconstruction after a mastectomy

  • Mandible is another term for the lower jaw

  • Mania is a mental disorder characterized by extreme excitement, happiness, overactivity, and agitation; usually refers to the high of the highs and lows experienced in manic- depressive disorder

  • Manic-depressive disorder is a mental disorder characterized by extreme mood swings, including either mania, depression, or a continuing shift between the two extremes

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  • Marfan's syndrome is a rare genetic disorder that affects connective tissue, leading to abnormalities of joints, bones, tendons, ligaments, arteries, and/or the heart

  • Mast cell is a type of cell present in most body tissues that releases substances in response to an allergen, which causes symptoms such as inflammation

  • Mastectomy is a surgical procedure in which all or part of the breast is removed to prevent the spread of cancer

  • Mastitis is inflammation of the breast, which is usually caused by a bacterial infection

  • Maxilla is one of two bones that form the upper jaw, the roof of the mouth, and the center portion of the face

  • Measles is an illness caused by a viral infection, causing a characteristic rash and a fever; primarily affects children

  • Meconium is thick, sticky, greenish-brown stool passed by a postmature fetus, or one experiencing fetal distress, into the amniotic fluid, or by an infant during the first couple of days after birth

  • Medial is a term used to describe something situated on or near the midline of the body or a body structure

  • Median nerve is a nerve running down the arm to the hand; controls muscle movement in the forearm and hand and conveys sensation from part of the hand

  • Mediastinoscopy is investigation of the central chest compartment using an endoscope that is inserted through an incision in the neck

  • Medulla is the center part of an organ or body structure; sometimes used to refer to the lower part of the brain stem

  • Medulloblastoma is a type of cancerous tumor, occurring in the section of the brain that controls posture and balance; found mainly in children

  • Megacolon is a severely swollen large intestine, causing severe constipation and abdominal bloating; may be present at birth or develops later

  • Megaloblastic anemia is a type of anemia in which a lack of the vitamin B12 or folic acid interferes with red blood cells and causes them to be enlarged and deformed, resulting in tiredness and weight loss

  • Meiosis is the type of cell division that occurs only in the ovaries and testicles, producing cells with half the genes of the original cell; these cells then form eggs and sperm

  • Melanin is the pigment that gives skin, hair, and eyes their coloring

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  • Melanoma is a skin tumor composed of cells called melanocytes

  • Menarche is the beginning of menstruation

  • Meniere's disease is a disorder of the inner ear, causing hearing loss, ringing in the ear, and the sensation that one's surroundings are spinning

  • Meninges is the three membranes that surround and protect the spinal cord and brain

  • Meningioma is a rare noncancerous tumor developing in the protective membranes covering the brain called the meninges; can cause headaches and problems with vision and mental function

  • Meningitis is inflammation of the meninges; usually caused by infection by a microorganism (meningitis caused by bacteria is life-threatening; viral meningitis is milder)

  • Meningocele is a protrusion of the meninges through an opening in the skull or spinal cord due to a genetic defect

  • Meniscectomy is surgical removal of all or part of a cartilage disk from a joint

  • Meniscus is a crescent-shaped pad of cartilage in joints that helps to reduce friction

  • Menopause is the period in a woman's life when menstruation stops, resulting in a reduced production of estrogen and cessation of egg production

  • Menorrhagia is excessive loss of blood during menstruation, which can be caused by disorders of the uterus

  • Menstrual cycle is the periodic discharge of blood and mucosal tissue from the uterus, occurring from puberty to menopause in a woman who is not pregnant

  • Menstruation is the shedding of the lining of the uterus during the menstrual cycle

  • Mesothelioma is a cancerous tumor occurring in the lining of the lungs and chest cavity, often associated with exposure to asbestos dust

  • Mesothelium is a tissue layer that lines the heart, abdomen, chest cavity, and lungs

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  • Messenger RNA is an RNA molecule that transports the information stored in DNA out of a cell's nucleus in order to make proteins

  • Metabolism is a general term for all of the chemical processes that occur in the body

  • Metabolite is any substance that takes part in a chemical reaction in the body

  • Metastasis is the spreading of a cancerous tumor to another part of the body through lymph, blood, or across a cavity; also sometimes refers to a tumor that has been produced in this way

  • Microbe is another term for a microorganism, especially one that causes disease

  • Microdiskectomy is surgical removal of the protruding part of a prolapsed disk

  • Microorganism is any tiny, single-celled organism (such as a bacterium, virus, or fungus)

  • Microsurgery is a surgical technique that uses a special binocular microscope to operate on tiny, delicate, or hard-to-reach tissues

  • Micturition syncope is fainting or feeling weak while standing at the toilet; caused by an abnormal heartbeat or a drop in blood pressure

  • Middle ear is the small cavity between the eardrum and inner ear; contains three tiny, linked bones that transmit sound to the inner ear

  • Midwifery is a profession concerned with providing care to a mother and baby during pregnancy and childbirth

  • Migraine is a severe headache, usually accompanied by vision problems and/or nausea and vomiting, and that typically recurs

  • Mineral is a substance that is a necessary part of a healthy diet (such as potassium, calcium, sodium, phosphorus, and magnesium)

  • Minipill is an oral contraceptive containing only the synthetic hormone progesterone (birth control pills contain estrogen and progesterone)

  • Miotic is a drug that causes the pupil to constrict

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  • Miscarriage is expulsion of a fetus before it has developed sufficiently to survive on its own

  • Mites is small eight-legged animals, many of which burrow and feed on blood

  • Mitosis is the process by which most cells divide in order to reproduce

  • Mitral insufficiency is a problem with the ability of the mitral valve in the heart to close, which causes the heart to pump harder and reduces its efficiency

  • Mitral stenosis is a condition in which the mitral valve in the heart becomes narrowed, making the heart work harder to pump blood; can lead to symptoms such as shortness of breath

  • Mitral valve is the valve in the heart that allows blood to flow from the left atrium to the left ventricle, but prevents blood from flowing back in

  • Mitral valve prolapse is a common condition in which the mitral valve in the heart is deformed, causing blood to leak back across the valve; characterized by a heart murmur and sometimes chest pain and disturbed heart rhythm

  • Modified radical mastectomy is a treatment for breast cancer in which the entire breast, a section of the chest muscle, and lymph nodes in the chest and underarm are removed

  • Molar tooth is large, strong teeth at the back of the jaw, primarily used to grind food

  • Mole is a brown to dark-brown spot on the skin that can be flat or raised

  • Molecule is the smallest unit of a substance that possesses its characteristics

  • Molluscum contagiosum is a viral infection that causes white bumps on the skin; usually clears up in a few months

  • Mongolian spot is a brown to blue-black spot on the lower back and buttocks at birth, caused by a concentration of pigment-producing cells; usually disappears by the age of 3 or 4 years

  • Monoclonal antibodies is an antibody that is produced in the laboratory so that it will react with only one specific foreign protein; used to help diagnose certain kinds of cancer

  • Mononucleosis is an infection caused by a virus that invades a type of white blood cell called a monocyte, causing fever, sore throat, and swollen lymph nodes

  • Monounsaturated fat is a type of fat that is thought to be beneficial in the prevention of coronary heart disease; found in foods such as olive oil and peanut oil

  • Morbidity is the state of being ill or having a disease

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  • Morning sickness is nausea and vomiting experienced early in a pregnancy, affecting about half of all pregnant women

  • Mortality is the death rate, measured as the number of deaths per a certain population; may describe the population as a whole, or a specific group within a population (such as infant mortality)

  • Motor nerve is a nerve that carries messages to a muscle that cause the muscle to contract

  • Motor neuron disease is degeneration of the nerves in the spinal cord and brain that are responsible for muscle movement, causing weakness and muscle deterioration

  • Mouth-to-mouth resuscitation is a method of artificial breathing in which someone rhythmically forces air into the lungs of a person who has stopped breathing

  • MRI is see Magnetic resonance imaging

  • MS is see Multiple sclerosis

  • Mucocele is a sac or body cavity that is swollen because of the production of mucus by the cells in its lining

  • Mucolytic is a drug that lessens the sticky quality of phlegm and makes it easier to cough up

  • Mucous membrane is the soft, pink layer of cells that produce mucus in order to keep body structures lubricated; found in structures such as the eyelids, respiratory tract, and urinary tract

  • Mucus is a slippery fluid produced by mucous membranes that lubricates and protects the internal surfaces of the body

  • Multiple myeloma is a cancer that causes uncontrolled production of white blood cells in the bone marrow

  • Multiple pregnancy is the presence of more than one fetus in the uterus, such as occurs with twins

  • Multiple sclerosis is a disease in which the protective coverings (myelin) of nerve fibers in the brain are gradually destroyed; symptoms vary from numbness to paralysis and loss of control of bodily function

  • Mumps is a viral infection that causes inflammation of salivary glands; primarily affects children

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  • Murmur is a characteristic sound (heard through a stethoscope) of blood flowing irregularly through the heart; can be harmless or may be an indication of disease

  • Muscle fibers is specialized, contracting cells that are bundled together to form muscles

  • Muscle relaxants is a group of drugs used to relieve muscle spasm and to treat conditions such as arthritis, back pain, and nervous system disorders such as stroke and cerebral palsy

  • Muscle wasting is the degeneration of a muscle (loss of bulk), caused by disease or starvation

  • Muscular dystrophy is a rare genetic disorder in which muscles degenerate gradually and strength is lost

  • Mutagen is anything that can increase the rate of abnormal change in cells, which can lead to cancer

  • Mutation is a change in the genetic information within a cell

  • Myalgia is the medical term for muscle pain

  • Myasthenia gravis is a disease in which the muscles, mainly those in the face, eyes, throat, and limbs, become weak and tire quickly; caused by the body's immune system attacking the receptors in the muscles that pick up nerve impulses

  • Mycobacterium is a type of slow-growing bacterium; resistant to the body's defense mechanisms and are responsible for diseases such as tuberculosis and leprosy

  • Mycoplasma is the smallest free-living microorganisms

  • Mycosis is any disease caused by a fungus

  • Mydriatic is a drug that causes the pupil to dilate (widen)

  • Myelin sheath is the fat- and protein-containing material that surrounds and protects some nerves

  • Myelitis is inflammation of the spinal cord, which can cause headaches, fever, muscle stiffness, pain, weakness, and eventually paralysis

  • Myelocele is protrusion of the spinal cord and its coverings out from the spine; one of the more severe forms of spina bifida

  • Myeloma is a cancer affecting cells in the bone marrow; sometimes used as an abbreviation for multiple myeloma

  • Myelosclerosis is buildup of fibrous connective tissue in the bone marrow, affecting the production of blood components

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  • Myocardial infarction is the death of an area of heart muscle as a result of being deprived of its blood supply; characterized by severe pain in the chest; commonly called a heart attack

  • Myocarditis is inflammation of the heart muscle, which can be caused by a virus, certain drugs, or radiation therapy

  • Myomectomy is the surgical removal of a noncancerous tumor from muscle

  • Myopathy is a muscle disease, usually one that results in the deterioration of muscle

  • Myopia is the medical term for nearsightedness

  • Myositis is muscle inflammation, causing pain and weakness

  • Myringotomy is a surgical opening in the eardrum that allows for drainage

  • Myxoma is a noncancerous tumor made of mucous material and fibrous connective tissue

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  • Narcolepsy is a disorder that causes excessive sleepiness during the day and frequent and uncontrollable episodes of falling asleep

  • Narcosis is a drug (or other chemical)-induced drowsiness or stupor

  • Narcotic is an addictive substance that blunts the senses; can cause confusion, stupor, coma, and death with increased dosages

  • Narcotic analgesics is a type of painkiller that blocks the transmission of pain signals in the brain; often cause tolerance (the need for higher amounts of the drug to produce the same effect) and drug dependence

  • Nasal septum is the section of the nose that divides the left and right nostrils; made of cartilage and bone and covered by a mucous membrane

  • Nasogastric tube is a thin, plastic tube that is inserted through the nose, down the esophagus, and into the stomach; used to drain, wash, or take samples from the stomach, or to feed very sick patients who cannot eat

  • Nasopharynx is the passageway connecting the back of the nose to the top of the throat

  • Natural childbirth is a technique of giving birth that stresses relaxation techniques so that the use of pain-relieving drugs can be minimized; also called prepared childbirth

  • Natural methods of family planning is methods of planning a family that focus on a woman's time of ovulation, either so that pregnancy can be avoided or conception is likely

  • Nausea is feeling the need to vomit

  • Nebulizer is an instrument that provides a drug in its misted form through a face mask; used for severe asthma attacks and for children who have asthma but cannot use an inhaler

  • Necrosis is the medical term for the death of tissue cells

  • Needle aspiration is the use of a thin, hollow needle and syringe to remove body fluid for examination

  • Needle biopsy is the use of a hollow, wide-diameter needle to remove a sample of tissue for examination

  • Neonate is a term used to describe a newborn infant from birth to 1 month of age

  • Nephrectomy is the surgical removal of one or both kidneys

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  • Nephritis is inflammation of one or both kidneys because of an infection, an abnormal immune system response, or a disorder of metabolism

  • Nephroblastoma is a fast-growing cancer of the kidneys that occurs most commonly in children under 4 years of age

  • Nephrons is the tiny filtering units of the kidney

  • Nephrosclerosis is the replacement of normal kidney structures with scar tissue

  • Nephrostomy is the surgical placement of a tube into the kidney to drain urine

  • Nephrotic syndrome is symptoms that result from damage to the filtering units of the kidney

  • Nerve is a bundle of fibers that transmit electrical messages between the brain and areas of the body; these messages convey sensory or motor function information

  • Nerve block is the dulling of sensation in an area of the body by injecting a painkiller into or around a nerve leading to that section of the body

  • Nerve cell is the basic unit of the nervous system; transmits chemical messages throughout the body

  • Nerve compression is pressure on a nerve, which can cause nerve damage and muscle weakness

  • Neuralgia is pain along the course of a nerve caused by irritation or damage to the nerve

  • Neural tube is the tube located along the back of an embryo that later develops into the spinal cord and brain

  • Neural tube defects is problems in the development of the spinal cord and brain in an embryo, such as the failure of the spine to enclose the spinal cord (spina bifida) and the failure of the brain to develop (anencephaly)

  • Neuritis is inflammation of a nerve, often characterized by pain, numbness, or tingling; also used to describe nerve damage and disease from causes other than inflammation

  • Neuroblastoma is a cancerous childhood tumor located in the adrenal glands or the sympathetic nervous system

  • Neurofibrillary tangles is abnormal spiral filaments on nerve cells in the brain; characteristic of Alzheimer disease

  • Neurofibromatosis is a condition in which connective tissue tumors occur on nerves in the skin

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  • Neuroma is a noncancerous tumor occurring in nerve tissue

  • Neuron is another term for a nerve cell

  • Neuropathy is disease, inflammation, or damage to the nerves connecting the brain and spinal cord to the rest of the body

  • Neurosis is relatively mild emotional disorders (such as mild depression and phobias)

  • Neurotoxins is chemicals that attack and damage nerve cells

  • Neurotransmitters is chemicals that transfer messages from one nerve cell to another or from a nerve cell to a muscle cell

  • Nevus is a marking on the skin; can be present at birth (birthmark) or develop later (such as a mole)

  • Niacin is a vitamin important in many chemical processes in the body; also known as vitamin B3

  • Night terrors is a form of nightmlare causing abrupt awakening in terror; occurs mostly in children

  • Nitrates is a group of drugs that widen blood vessels; used to treat insufficient blood supply to the heart (angina pectoris) and reduced pumping efficiency of the heart (heart failure)

  • Nocturia is urination or a sleep-disturbing need to urinate during the night

  • Nocturnal emission is ejaculation of semen during sleep, which is normal in adolescent males; commonly called a wet dream

  • Node is a small, rounded tissue mass

  • Nodule is a small lump of tissue that is usually abnormal; can form under the skin or protrude

  • Nondisjunction is an error that occurs during the division of sex chromosomes, causing either too much or too little genetic information to be placed in an egg or sperm when it is formed

  • Non-Hodgkin's lymphoma is any cancer in lymphoid tissue (found mostly in the spleen and lymph glands) that is not Hodgkin's disease

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  • Non-insulin-dependent diabetes is a type of diabetes mellitus that occurs mainly in those over 40 who are overweight; it is usually treated with diet changes and drugs that increase production of insulin by the pancreas (also known as type II diabetes mellitus)

  • Noninvasive is a term that is used to describe medical procedures that do not enter or penetrate the body; also refers to noncancerous tumors that do not spread to other sections of the body

  • Nonnarcotic analgesic is a drug that relieves pain by blocking the production of chemicals that stimulate pain-sensing nerves

  • Norepinephrine is a hormone that regulates blood pressure by causing blood vessels to narrow and the heart to beat faster when blood pressure drops

  • NSAID is see Nonsteroidal anti-inflammatory drug

  • Nucleic acids is substances found in every living organism that provide the instructions for development; includes DNA and RNA

  • Nucleus is the center or most important point of an object

  • Numbness is the lack of sensation in a part of the body because of interruption of nerve impulses

  • Nurse-midwife is a registered nurse who specializes in the care of a mother and child during pregnancy, labor, and delivery

  • Nutrient is any substance that the body can use to maintain its health

  • Nystagmus is persistent, rapid, involuntary movement of the eyes

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  • Obesity is a condition in which there is an excess of body fat; used to describe those who weigh at least 20 percent more than the maximum amount considered normal for their age, sex, and height

  • Obsessive-compulsive disorder is a mental disorder in which a person is obsessed with certain thoughts, leading them to repeatedly perform specific acts; for example, constantly washing the hands out of fear of germs and dirt

  • Obstructive sleep apnea is the blockage of the airways during sleep, which causes breathing to stop for very short periods of time, commonly caused by excessive relaxation of muscles at the back of the throat

  • Occlusion is the blocking of an opening or passageway in the body

  • Occult blood is blood in the feces that can be detected only by chemical tests

  • Occupational therapy is treatment to relearn physical skills lost as a result of an illness or accident

  • Ocular is describes something related to the eyes

  • Oligodendroglioma is a rare type of cancerous brain tumor that occurs most commonly in the cerebrum

  • Oligohydramnios is an unusually small amount of amniotic fluid surrounding the fetus in the uterus, which can lead to complications with the pregnancy

  • Oligospermia is a low level of sperm in the semen; one of the main causes of infertility in men

  • Oncogenes is genes that, when altered by environmental factors or viruses, can cause abnormal cell growth

  • Oocyte is an egg cell that has not developed completely

  • Oophorectomy is the surgical removal of one or both ovaries; used to treat the growth of ovarian cysts or tumors

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  • Open heart surgery is any operation in which the heart is stopped temporarily and a machine is used to take over its function of pumping blood throughout the body

  • Ophthalmologist is a doctor who specializes in care of the eyes; treats eye diseases and disorders

  • Ophthalmoscopy is examination of the inside of the eye using a lighted viewing instrument

  • Opportunistic infection is infection by organisms that would be harmless to a healthy person, but cause infection in those with a weakened immune system (for example, persons with AIDS or chemotherapy patients)

  • Optic is pertaining to the eyes

  • Optician is a person who specializes in the making and adjustment of eyeglasses and contact lenses

  • Optic nerves is the pair of nerves that carry visual information from the retina to the brain

  • Optic neuritis is inflammation of the optic nerve, often causing a partial loss of vision

  • Oral contraceptives is drugs taken in pill form to prevent pregnancy; contain synthetic progesterone and estrogen hormones

  • Orbit is the socket in the skull that contains the eyeball, along with its blood vessels, nerves, and muscles

  • Orchiectomy is the surgical removal of one or both of the testicles

  • Orchiopexy is an operation to correct an undescended testicle

  • Orchitis is inflammation of a testicle, which can be caused by infection with the mumps virus

  • Organ donation is an agreement to allow one or more organs to be removed and transplanted into someone else

  • Organism is any single, functioning form of life

  • Orgasm is involuntary contraction of genital muscles experienced at the peak of sexual excitement

  • Orphan drugs is drugs used to treat rare diseases; not normally produced because potential sales are small

  • Orthopnea is breathing difficulty experienced while lying flat; can be a symptom of heart failure or asthma

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  • Orthotic is a device used to correct or control deformed bones, muscles, or joints

  • Osgood-Schlatter disease is painful enlargement and inflammation of the area of the shinbone just below the knee, usually occurring in adolescent boys

  • Osmosis is the process of passage of the solvent portion of a lesser-concentrated solution through a semipermeable membrane into a higher-concentrated solution until the two solutions are equal in concentration; plays an important role in water distribution in the body

  • Osteochondritis dissecans is bone degeneration inside of a joint, causing small pieces of bone and cartilage to become detached

  • Osteochondroma is a noncancerous tumor made up of bone and cartilage

  • Osteoclast is a cell that breaks down unwanted bone tissue; also refers to a device for fracturing a bone to correct a deformity

  • Osteogenesis imperfecta is a genetic disorder in which bones are abnormally fragile, leading to multiple breaks and deformity

  • Osteolysis is the softening and destruction of bone

  • Osteoma is a noncancerous bone tumor

  • Osteomalacia is the loss of minerals and softening of bones because of a lack of vitamin D; called rickets in children

  • Osteomyelitis is the inflammation of bones and bone marrow because of an infection, usually caused by bacteria

  • Osteopetrosis is a rare hereditary disorder in which bones become harder and more dense, causing them to break more easily

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  • Osteoporosis is a condition in which bones become less dense, more brittle, and fracture easily

  • Osteosclerosis is an abnormal increase in density and hardness of bone

  • Otalgia is the medical term for an earache

  • Otitis externa is inflammation of the outer ear due to an infection; commonly called swimmer's ear

  • Otitis media is inflammation of the middle ear (between the eardrum and inner ear) because of the spread of an infection from the nose, sinuses, and throat

  • Otorrhea is a discharge from an inflamed ear

  • Otosclerosis is progressive deafness caused by bone formation around structures in the middle ear

  • Ototoxicity is harmful effect that some drugs have on the organs or nerves in the ears, which can lead to hearing and balance problems

  • Ovaries is two almond-shaped glands located at the opening of the fallopian tubes on both sides of the uterus; produce eggs and the sex hormones estrogen and progesterone

  • Overdose is an excessively large dose of a drug, which can lead to coma and death

  • Ovulation is the development and release of the egg from the ovary, which usually occurs halfway through a woman's menstrual cycle

  • Ovum is another term for an egg cell

  • Oxidation is a chemical reaction involving active sources of oxygen (called oxygen free radicals) that damages cells

  • Oximetry is determination of the amount of oxygen in the blood by measuring the amount of light transmitted through an area of skin

  • Oxygen is a gas that is colorless, odorless, and tasteless; essential to almost all forms of life

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  • Oxygen free radicals is active forms of oxygen found in pollution, cigarette smoke, and radiation that can damage cells and are believed to play a role in the aging process and cancer

  • Oxytocin is a hormone produced in the pituitary gland that causes contraction of the uterus during childbirth and stimulation of milk flow during breast-feeding

  • Ozone is a poisonous form of oxygen that is present in the earth's upper atmosphere, where it helps to screen the earth from damaging ultraviolet rays

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  • Pacemaker is a small electronic device that is surgically implanted to stimulate the heart muscle to provide a normal heartbeat

  • Paget's disease is a disorder occurring in the middle-aged and elderly in which bone does not form properly, causing bone weakening, thickening, and deformity

  • Palate is the roof of the mouth

  • Pallor is abnormally pale skin; usually refers to the skin of the face

  • Palpation is the use of the hands to feel parts of the body to check for any abnormalities

  • Palpitation is an abnormally rapid and strong heartbeat

  • Palsy is loss of sensation or ability to move

  • Pancreas is a long gland located behind the stomach that produces enzymes that help to break down food and hormones (insulin and glucagon) that help to regulate glucose levels in the blood

  • Pancreatitis is inflammation of the pancreas, which is often caused by alcohol abuse

  • Panic disorder is an emotional disorder characterized by attacks of anxiety that have no normal causes; usually made worse by stress

  • Papilloma is a tumor occurring on the skin or mucous membranes; usually not cancerous

  • Pap smear is a test in which cells are scraped off the cervix and examined for abnormalities; used to detect changes that might precede cervical cancer and to diagnose viral infections such as herpes simplex

  • Paracentesis is the insertion of a needle into a body cavity to relieve pressure, inject a drug, or remove a sample for analysis

  • Paralysis is the inability to use a muscle because of injury to or disease of the nerves leading to the muscle

  • Paramedic is a person trained to give first aid and other emergency medical care

  • Paranoia is a disorder in which a person becomes overly suspicious and emotionally sensitive

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  • Paraphimosis is strangulation of the head of the penis by a tight or inflamed foreskin that has been pulled back

  • Paraplegia is complete or partial loss of sensation and movement of the legs

  • Parasite is an organisms that lives on or in other organisms, from which it obtains nutrients

  • Parathyroid glands is small glands located in the neck that produce a hormone that regulates the levels of calcium in the blood

  • Parathyroid hormone is a hormone released by the parathyroid glands that plays a role in controlling calcium levels in the blood

  • Parenteral is the introduction of a substance into the body by any route other than the digestive tract, such as through a vein or muscle

  • Paresthesia is numbness or tingling in the skin; commonly referred to as "pins and needles"

  • Parkinson's disease is a brain disorder in which there is a lack of the chemical messenger dopamine, which helps control muscle movement; leads to muscle stiffness, weakness, and trembling

  • Paronychia is a bacterial or yeast infection of the skin around the nail

  • Parotid glands is salivary glands located in the mouth near the ears

  • Paroxysm is a sudden attack or worsening of a disease's symptoms

  • Partial mastectomy is a treatment for breast cancer in which a tumor is removed, along with the skin covering it and some of the surrounding tissues and muscles

  • Partial seizure is an abnormal electrical discharge in a certain area of the brain, affecting only certain functions

  • Passive exercise is exercise of an injured part of the body involving no effort from that injured part

  • Passive smoking is a nonsmoker inhaling the cigar, cigarette, or pipe smoke of others (called second-hand smoke) in the same area, which increases the nonsmoker's risk of cancer and respiratory disorders

  • Patella is the medical term for the kneecap

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  • Patent is not obstructed; open

  • Patent ductus arteriosus is a genetic disorder of the heart in which a channel connecting the pulmonary artery and the aorta fails to close and the heart must work harder to supply the body with blood

  • Paternity testing is use of blood tests to match up DNA or specific blood proteins to determine whether a man is the father of a child

  • Pathogen is any substance capable of causing a disease; usually refers to a disease-causing microorganism

  • Pathogenesis is the production and development of a disease or disorder

  • Patient-controlled analgesia is a system for administering pain-killing drugs in which the amount of drug delivered is controlled by the patient

  • Peak flow measurement is the maximum speed that air is exhaled from the lungs; used to diagnose asthma or to determine the effectiveness of asthma medications

  • Pectoral muscles is the muscles of the upper part of the chest that move the arm across the body, raise some of the ribs, and move the shoulders

  • Pellagra is a deficiency of the vitamin niacin; causes dermatitis, diarrhea, and mental disorders

  • Pelvic inflammatory disease is inflammation of a woman's internal reproductive organs, usually as a result of a bacterial infection; one of the most common causes of pelvic pain and infertility in women

  • Pelvis is the group of bones in the lower part of the trunk that support the upper body and protect the abdominal organs

  • Penile function tests is tests used to determine the cause of impotence, including blood tests and nerve function tests

  • Penile implant is an inflatable device surgically inserted into the penis that allows a man with impotence to have sexual intercourse

  • Penis is the external male reproductive organ, which passes urine and semen out of the body

  • Pepsin is the enzyme found in gastric juice that helps digest protein

  • Peptic ulcer is an erosion in the lining of the esophagus, stomach, or small intestine, usually caused in part by the corrosive action of gastric acid

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  • Percutaneous is a procedure that is performed through the skin, such as an injection

  • Perforation is a hole in an organ or body structure caused by disease or injury

  • Pericardial effusion is fluid buildup inside of the pericardium, affecting the performance of the heart

  • Pericarditis is inflammation of the membranous sac that covers the heart, causing chest pain and fever

  • Pericardium is the membranous sac that covers the heart and the base of the blood vessels that are attached to the heart

  • Perinatal is occurring just before or just after birth

  • Periosteum is the tissue covering bones, except the surfaces in joints

  • Peripheral vascular disease is the narrowing of blood vessels in the legs or arms, causing pain and possibly tissue death (gangrene) as a result of a reduced flow of blood to areas supplied by the narrowed vessels

  • Peristalsis is wavelike movement of smooth muscle-containing tubes, such as the digestive tract

  • Peritoneum is the membrane that lines the abdominal cavity and covers the abdominal organs

  • Pernicious anemia is an anemia caused by a failure to absorb vitamin B12; which is essential in the production of normal red blood cells

  • Perthes' disease is inflammation of the growing head of a femur; a type of osteochondritis juvenilis

  • Pertussis is a bacterial infection of the respiratory tract characterized by short, convulsive coughs that end in a whoop sound when breath is inhaled (commonly called whooping cough); mainly affects children

  • Petit mal is a seizure characterized by loss of awareness for brief periods

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  • Peutz-Jeghers syndrome is a genetic disorder in which there are polyps in the small intestine and brown melanin spots on the lips, mouth, fingers, and toes

  • pH is a measure of the acidic or basic character of a substance

  • Phagocyte is an immune system cell that can surround and digest foreign bodies, unwanted cellular material, and microorganisms

  • Phantom limb is the sensation of a limb after it has been amputated

  • Pharmacology is the study of medications, including drug development

  • Pharyngitis is inflammation of the throat (the pharynx), causing sore throat, fever, earache, and swollen glands

  • Pharynx is the throat; the tube connecting the back of the mouth and nose to the esophagus and windpipe

  • Phenothiazines is a group of drugs used as antipsychotics, antihistamines, and antiemetics

  • Phenylketonuria is a hereditary disorder in which the enzyme that converts the amino acid phenylalanine into another amino acid is defective, meaning phenylalanine must be kept out of the diet

  • Pheochromocytoma is a noncancerous tumor of cells that produce epinephrine and norepinephrine, causing higher levels of these hormones in the blood and an increase in blood pressure

  • Phimosis is tightness of the foreskin, which prevents it from being moved back over the head of the penis

  • Phlegm is mucus and other material produced by the lining of the respiratory tract; also called sputum

  • Phobia is a persisting fear of and desire to avoid something

  • Phosphates is salts containing phosphorus; essential to some body functions such as the bones and teeth

  • Phospholipids is fatty substances that make up the membranes surrounding cells

  • Phosphorus is a mineral that is an important part of structures such as bones, teeth, and membranes in the body; also involved in numerous other chemical reactions

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  • Photophobia is an abnormal sensitivity of the eyes to light

  • Photosensitivity is an abnormal reaction to sunlight, which usually occurs as a rash

  • Physical therapy is the treatment of injuries or disorders using physical methods, such as exercise, massage, or the application of heat

  • Phytochemicals is chemicals in plants that might help protect against disorders such as cancer

  • Pica is a desire to eat materials that are not food

  • Pickwickian syndrome is extreme obesity along with shallow breathing, sleep apnea, excessive sleepiness, and heart failure

  • PID is see Pelvic inflammatory disease

  • Pigmentation is the coloration of the skin, hair, and eyes by the pigment melanin

  • Pinkeye is inflammation of the membrane that covers the white of the eyes and lines the eyelids, causing redness, discomfort, and a discharge; can be caused by infection or allergies

  • Pinworm is a small parasite worm that can live in the intestines; commonly affects children

  • Pituitary gland is a small, round gland located at the base of the brain that releases hormones that control other glands and body processes

  • Pityriasis alba is a common childhood or adolescent disorder in which there are pale, scaly patches on the skin of the face

  • Pityriasis rosea is a mild skin condition in which flat, scaly spots occur on the trunk and upper arms

  • Pivot joint is a joint designed for rotational movement

  • PKU is see Phenylketonuria

  • Placebo is a chemically inactive substance given in place of a drug to test how much of a drug's effectiveness can be attributed to a patient's expectations that the drug will have a positive effect

  • Placebo effect is the positive or negative response to a drug that is caused by a person's expectations of a drug rather than the drug itself

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  • Placenta is an organ formed in the uterus during pregnancy that links the blood of the mother to the blood of the fetus; provides the fetus with nutrients and removes waste

  • Placental abruption is the separation of the placenta from the wall of the uterus before childbirth, which causes severe bleeding that threatens the life of the mother and the fetus

  • Placental insufficiency is a disorder occurring during pregnancy in which the placenta does not function properly, causing the fetus to be deprived of nutrients

  • Placenta previa is a disorder in which the placenta develops at the lower section of the uterus (close to or covering the cervix); varies in severity, from no effect on a pregnancy to vaginal bleeding and danger to the mother and the fetus

  • Plague is a serious infectious disease transmitted to humans through bites of rodent fleas

  • Plantar reflex is the normal curling of the toes downward when the sole of the foot is stroked

  • Plantar wart is a rough-surfaced, hard spot on the sole of the foot that is caused by a virus

  • Plaque is an area of buildup of fat deposits in an artery, causing narrowing of the artery and possibly heart disease; dental plaque refers to a coating on the teeth, consisting of saliva, bacteria, and food debris, which causes tooth decay

  • Plasma is the liquid part of the blood, containing substances such as nutrients, salts, and proteins

  • Plasma cell is a white blood cell that makes antibodies

  • Plasmapheresis is a procedure for removing unwanted substances from the blood in which blood is drawn, its plasma is separated and replaced, and the cleansed blood is returned to the body

  • Platelet is the smallest particle found in the blood, which plays a major role in forming blood clots

  • Pleura is the double-layered membrane that lines the lungs and chest cavity and allows for lung movement during breathing

  • Pleural effusion is a buildup of fluid between the membranes that line the lungs and chest cavity (the pleura); causes compression of the lungs, which leads to breathing difficulty

  • Pleural rub is a rubbing sound produced by inflamed pleural membranes that can be heard when breathing

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  • Pleurisy is inflammation of the lining of the lungs and chest cavity, usually caused by a lung infection; characterized by sharp chest pain

  • Plummer-Vinson syndrome is difficulty swallowing due to an abnormal web of tissue across the upper part of the esophagus

  • PMS is see Premenstrual syndrome

  • Pneumoconiosis is a respiratory disease caused by dust inhalation Pneumocystis pneumonia]] is an opportunistic infection of the lungs caused by a single- celled parasite

  • Pneumonia is inflammation of the lungs due to a bacterial or viral infection, which causes fever, shortness of breath, and the coughing up of phlegm

  • Pneumothorax is a condition in which air enters the space between the chest wall and the lungs, causing chest pain and shortness of breath; may occur spontaneously or be the result of a disease or an accident

  • Poliomyelitis is an infectious disease caused by a virus; usually causes only mild symptoms but in rare cases can attack the brain and spinal cord and cause paralysis or death

  • Polycystic ovary syndrome is a hereditary disease characterized by multiple cysts on the ovaries, obesity, excessive hairiness, infertility, and irregular menstruation

  • Polycythemia is an increased amount of red blood cells in the blood

  • Polydactyly is the presence of an excessive number of fingers or toes

  • Polymyalgia rheumatica is a rare disease of the elderly, characterized by muscle stiffness and pain in the hips, thighs, shoulders, and neck

  • Polymyositis is an autoimmune disease of connective tissue in which muscles weaken and become inflamed

  • Polyp is a growth that occurs on mucous membranes such as those in the nose and intestine; bleeds easily and can become cancerous

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  • Polysaccharide is a complex carbohydrate composed of three or more simple carbohydrate molecules joined together

  • Polyunsaturated fat is a fat or oil that contains well below the maximum number of hydrogen atoms possible; thought to reduce the risk of coronary heart disease

  • Polyuria is the excessive production of urine; can be a symptom of various diseases, most notably diabetes mellitus

  • Porphyria is a group of genetic disorders in which substances called porphyrins build up in the blood, often causing rashes brought on by exposure to sunlight and reactions to certain drugs

  • Portal vein is the vein connecting the stomach, intestines, and spleen to the liver

  • Positron emission tomography scanning is an imaging method in which substances emitting positrons (positively charged particles) are introduced into the body, and detectors connected to a computer are used to form images of the tissues

  • Posterior is describes something that is located in or relates to the back of the body

  • Postmortem examination is examination of a body after death to determine the cause of death; commonly called an autopsy

  • Postnatal is describes something that occurs after birth, usually to the baby

  • Postpartum is a term that describes something that occurs after childbirth, usually to the mother

  • Post-traumatic stress disorder is feelings of anxiety experienced after a particularly frightening or stressful event, which include recurring dreams, difficulty sleeping, and a feeling of isolation

  • Postural drainage is drainage of mucus from specific areas of the lungs by placing the body in a specific position

  • Postural hypotension is unusually low blood pressure that occurs after suddenly standing or sitting up

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  • Potassium is a mineral that plays an important role in the body, helping to maintain water balance, normal heart rhythm, conduction of nerve impulses, and muscle contraction

  • Precancerous is describes a condition from which cancer is likely to develop

  • Preeclampsia is a serious disorder that occurs in the second half of pregnancy, in which a woman experiences high blood pressure, fluid retention, nausea, and headaches; if not treated it can lead to eclampsia

  • Premature labor is labor that begins before the full term of pregnancy (about 37 weeks)

  • Premature rupture of membranes is the rupture of the sac that holds the fluid surrounding the fetus before the full term of pregnancy (about 37 weeks)

  • Premedication is drugs, usually painkillers, taken 1 to 2 hours before surgery

  • Premenopausal is a term that describes the period of a few years in a woman's life just before menopause

  • Premenstrual syndrome is physical and emotional changes that occur in a woman 1 or 2 weeks before menstruation, at or after ovulation; characterized by irritability, tension, depression, and fatigue

  • Prenatal testing is tests performed on a pregnant woman or her fetus to prevent or diagnose abnormalities

  • Prepared childbirth is a technique in which a pregnant woman tries to minimize use of pain-relief medications during childbirth by learning relaxation techniques

  • Presbycusis is the loss of hearing that occurs naturally with age

  • Presbyopia is the loss of the ability to focus the eyes on near objects that occurs naturally with age, as a result of loss of elasticity of the lens of the eyes

  • Pressure point is specific points on the body where external pressure can be applied to prevent excessive arterial bleeding

  • Pressure sore is an ulcer (erosion) on the skin that is a result of being bedridden; commonly called a bedsore

  • Priapism is a painful, persistent erection without sexual arousal, requiring emergency treatment

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  • Prickly heat is a rash involving small, red, itchy spots and a prickly sensation that usually appears where sweat builds up

  • Primary is a disease that began in the affected location

  • Prion is an agent that is believed to cause several degenerative brain diseases

  • Proctitis is inflammation of the rectum, which causes soreness and sometimes mucus and/or pus in the stool

  • Proctoscopy is examination of the rectum using a viewing instrument

  • Productive cough is a cough that brings up phlegm, which is the body's natural way of clearing blocked airways

  • Progeria is an extremely rare condition in which the body ages prematurely

  • Progesterone is a female sex hormone that plays many important roles in reproduction, including the thickening of the lining of the uterus during the menstrual cycle; and during pregnancy, the functioning of the placenta, and the initiation of labor

  • Prognosis is a doctor's probable forecast of the effects and outcome of a disease

  • Prolactin is a hormone released by the pituitary gland that is responsible for the development of breasts and milk production in females

  • Prolapse is the displacement of an organ from its normal position to a new one

  • Proprioception is the body's system for determining its position relative to the outside world

  • Prostatectomy is the partial or complete surgical removal of the prostate gland

  • Prostate gland is an organ located under the bladder that produces a large part of the semen

  • Prostatism is symptoms caused by an enlarged prostate gland, including difficulty with urination

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  • Prostatitis is inflammation of the prostate gland, usually due to a bacterial infection spread from the urethra

  • Prosthesis is an artificial replacement for a missing part of the body

  • Proteins is large molecules made up of amino acids that play many major roles in the body, including forming the basis of body structures such as skin and hair, and important chemicals such as enzymes and hormones

  • Prothrombin time is the time it takes for a sample of blood to clot after substances that speed clotting time have been added; used to measure the effect of anticoagulants

  • Proton pump inhibitor is a drug used to treat peptic ulcers that reduces the amount of gastric acid produced

  • Proto-oncogene is a gene that is normally inactive but can become a cancer-causing oncogene if made active

  • Protozoan is a simple, single-celled organism

  • Proximal is located nearer to a central point of reference on the body, such as the trunk

  • Pruritus is the medical term for itching

  • Pseudogout is a form of arthritis with symptoms similar to gout that results from the depositing of calcium salts in a joint

  • Psittacosis is a chlamydial infection resembling influenza that is spread to humans by the droppings of infected birds

  • Psoralens is drugs that contain chemicals derived from plants; used to treat the skin disorders psoriasis and vitiligo

  • Psoriasis is a skin disorder characterized by patches of thick, red skin often covered by silvery scales

  • Psoriatic arthritis is a form of arthritis that develops as a complication of the skin disorder psoriasis

  • Psychogenic is resulting from psychological or emotional disorders

  • Psychological is relating to the mind and the processes of the mind

  • Psychosis is a mental disorder in which a serious inability to think, perceive, and judge clearly causes loss of touch with reality

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  • Psychosomatic is describes a physical condition that is influenced by psychological or emotional factors

  • Psychotherapy is the treatment of mental and emotional disorders using psychological methods, such as counseling, instead of physical means

  • Ptosis is the drooping of the upper eyelid

  • Puberty is the period of time (usually between the ages of 10 and 15) during which sexual development occurs, allowing reproduction to become possible

  • Pubic louse is a small insect that lives in pubic hair, feeds on blood, and is usually spread by sexual contact; pubic lice are popularly called "crabs"

  • Pudendal block is a local anesthesia procedure used during childbirth, causing the lower part of the vagina to be insensitive to pain

  • Pudendum is the external genitals, usually referring to the female

  • Puerperal sepsis is infection of the female genital tract following childbirth, abortion, or miscarriage

  • Puerperium is the time period after childbirth (about 6 weeks) during which a woman's body returns to its normal physical state

  • Pulmonary artery is the artery that supplies the lungs with blood from the heart

  • Pulmonary edema is the buildup of fluid in lung tissue, which is usually caused by heart failure

  • Pulmonary fibrosis is a condition in which the tissue of the lungs has become thick and scarred, usually because of inflammation caused by lung conditions such as pneumonia or tuberculosis

  • Pulmonary heart valve is the heart valve that stops blood pumped to the lungs from leaking back into the heart

  • Pulmonary hypertension is increased blood pressure in the arteries supplying blood to the lungs; caused by increased resistance to blood flow in the lungs, usually a result of a lung disease

  • Pulmonary insufficiency is a rare defect in the pulmonary heart valve in which it fails to close properly after each muscle contraction, allowing blood to leak back into the heart; weakens the heart's pumping ability

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  • Pulp is the soft tissue inside of a tooth that contains blood vessels and nerves

  • Pulse is the expansion and contraction of a blood vessel due to the blood pumped through it; determined as the number of expansions per minute

  • Pupil is the opening at the center of the iris in the eye that constricts (contracts) and dilates (widens) in response to light

  • Purpuric rash is areas of purple or reddish-brown spots on the skin, which are caused by bleeding from underlying tissues

  • Pus is a thick, yellowish or greenish fluid that contains dead white blood cells, tissues, and bacteria; occurs at the site of a bacterial infection

  • Pustule is a small blister containing pus

  • PUVA is a form of phototherapy that combines the use of psoralens and ultraviolet light to treat skin disorders

  • Pyelonephritis is inflammation of the kidney, usually due to a bacterial infection

  • Pyloric sphincter is a circular muscle located at the junction of the stomach and small intestine that controls the passage of food into the small intestine

  • Pyloric stenosis is narrowing of the outlet located at the junction of the stomach and small intestine

  • Pyloroplasty is surgical widening of the outlet between the stomach and small intestine

  • Pyrexia is a body temperature of above 98.6°F in the mouth or 99.8°F in the rectum

  • Pyrogen is any substance that causes a fever

  • Pyuria is the presence of white blood cells in the urine; usually an indication of kidney or urinary tract infection

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  • Quadriceps muscle is the muscle (consisting of 4 distinct parts) located at the front of the thigh that straightens the leg

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  • Rabies is an infectious viral disease primarily affecting animals; can be transmitted to humans through an infected animal's bite; if untreated, can result in paralysis and death

  • Radial keratotomy is a surgical procedure for correcting nearsightedness in which tiny cuts are made in the cornea to change its shape and focusing properties

  • Radiation is a variety of types of energy, such as X-rays and ultraviolet

  • Radiation therapy is treatment of a disease, such as cancer, using forms of radioactivity that damage or destroy abnormal cells

  • Radical surgery is treatment of disease by surgically removing all tissue that is or may be affected

  • Radiculopathy is any disease of the nerve roots; can be caused by disk prolapse, arthritis, and other problems

  • Radioallergosorbent test is a blood test performed to help determine the cause of an allergy by detecting the presence of antibodies to various allergens

  • Radiography is the formation of images of the inside of the body using radiation projected through the body and onto film; a radiograph is also called an X-ray

  • Radionuclide scanning is an imaging technique in which a radioactive substance is introduced into the body and its emitted radiation is detected; specific organs can be studied according to the amount of the radioactive substance that they absorb

  • Radius is one of the two long bones of the forearm, located on the thumb side of the arm

  • Radon is a colorless, odorless, tasteless radioactive gas that is produced by materials in soil, rocks, and building materials; suspected of causing cancer

  • Rales is abnormal crackling or bubbling sounds heard in the lungs during breathing

  • Rash is an area of inflammation or a group of spots on the skin

  • Raynaud's disease is a condition in which the fingers and toes become pale when exposed to cold or emotional stress, owing to sudden narrowing of the arteries that supply them with blood

  • Receptor is a nerve cell that responds to a stimulus and produces a nerve impulse; also refers to the area on the surface of a cell that a chemical must bind to in order to have its effect

  • Recessive gene is a gene that does not produce its effect when it occurs with a dominant gene, but produces its effect only when there are two copies of it

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  • Rectal prolapse is bulging of the lining of the rectum through the anus, usually due to straining during a bowel movement

  • Rectum is a short tube located at the end of the large intestine, which connects the intestine to the anus

  • Red blood cell is a doughnut-shaped blood cell that carries oxygen from the lungs to body tissues

  • Referred pain is pain felt in a part of the body remote from the site where pain originates

  • Reflex is an automatic, involuntary response of the nervous system to a stimulus

  • Reflux esophagitis is the backflow of gastric acid from the stomach to the lower esophagus, owing to a defect in the valve that separates them

  • Regurgitation is the backflow of fluid; can refer to food and drink flowing back up from the stomach into the mouth or blood flowing back into the heart through a defective heart valve

  • Rehabilitation is treatment for an injury or illness aimed at restoring physical abilities

  • Rehydration is treatment for dehydration (an abnormally low level of water in the body) in which levels are restored by taking fluids containing water, salt, and glucose by mouth or, if severe, through a vein

  • Reiter's syndrome is a disorder characterized by inflammation of the joints, urethra, and sometimes the conjunctiva

  • Relapse is the return of a disease or symptom after it had disappeared

  • Remission is the temporary disappearance of a disease or its symptoms, either partially or completely; also refers to the time period in which this occurs

  • REM sleep is rapid eye movement sleep; the stage of sleep in which dreaming occurs

  • Renal colic is severe pain on one side of the lower back, usually as a result of a kidney stone

  • Renal tubular acidosis is inability of the kidneys to remove sufficient amounts of acid from the body, making the blood more acidic than normal

  • Renin is an enzyme that plays a role in increasing a low blood pressure

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  • Reproductive system is the organs and structures that allow men and women to have sexual intercourse and produce children

  • Resection is partial or complete surgical removal of a diseased organ or structure

  • Respiration is the process by which oxygen is taken in and used by tissues in the body and carbon dioxide is released

  • Respiratory distress syndrome is a condition experienced after an illness or injury damages the lungs, causing severe breathing difficulty and resulting in a life-threatening lack of oxygen in the blood

  • Respiratory failure is the failure of the body to exchange gases properly, which leads to a buildup of carbon dioxide and a lack of oxygen in the blood

  • Resting pulse is the pulse rate when a person is not experiencing any physical activity or mental stress

  • Retina is a membrane lining the inside of the back of the eye that contains light-sensitive nerve cells that convert focused light into nerve impulses, making vision possible

  • Retinal artery occlusion is obstruction of an artery that supplies blood to the retina, resulting in some degree of temporary or permanent blindness

  • Retinitis pigmentosa is gradual loss of the field of vision, owing to a degeneration of the light-sensitive nerve cells of the retina

  • Retinoblastoma is a hereditary, cancerous tumor of the retina affecting infants and children

  • Retinoid is a substance resembling vitamin A that is used to treat skin conditions such as acne and has been reported to reduce skin wrinkling

  • Retinopathy is any disease or disorder of the retina; usually refers to damage to the retina caused by high blood pressure or diabetes mellitus

  • Retinoscopy is a method of determining focusing errors of the eye in which light is shined through the pupil and the reflected beam is measured

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  • Retroviruses is a group of viruses that are made up of RNA instead of DNA, including HIV and the virus that causes T-cell leukemia

  • Reye's syndrome is a rare disorder mainly affecting those under the age of 15 that is characterized by brain and liver damage following a viral infection such as chickenpox or the flu; may be linked to taking aspirin to treat a viral infection

  • Rh blood group is a blood group classifying whether the substances called Rhesus (Rh) factors are present on the surface of red blood cells; the "positive" or "negative" designation in blood classification (for example, "O negative")

  • Rheumatic fever is a disorder that follows a throat infection by the streptococcus bacteria and causes inflammation in body tissues

  • Rheumatoid arthritis is a condition in which joints in the body become inflamed, stiff, painful, and sometimes deformed because of the body's own immune system attacking the tissues

  • Rheumatoid factors is antibodies that are present in about 80% of people with rheumatoid arthritis; their detection through blood testing can help to diagnose the disorder

  • Rh immunoglobulin is a substance used to prevent a woman who is Rh incompatible with her fetus from becoming Rh sensitized

  • Rh incompatibility is a condition in which a pregnant woman's Rh factor does not match that of the fetus; can lead to the production of antibodies by the mother that destroy the fetus' red blood cells

  • Rhinitis is inflammation of the mucous membrane lining the nose, which can cause sneezing, runny nose, congestion, and pain; when caused by substances in the air, it is called allergic rhinitis or hay fever

  • Rhinophyma is a bulb-shaped deformity and redness of the nose as a result of severe rosacea

  • Rhinoplasty is surgery that changes the structure of the nose, either to improve appearance or to correct a deformity or injury

  • Rh sensitized is a condition in which a woman who has a negative Rh factor develops permanent antibodies against Rh-positive blood as a result of exposure to the blood of her fetus; can cause fetal hemolysis in subsequent pregnancies

  • Rhythm method is a method of preventing pregnancy in which a couple does not have sexual intercourse during the days of the menstrual cycle during which fertilization can occur

  • Riboflavin is a vitamin belonging to the vitamin B complex that is important in many processes in the body and helps to maintain healthy skin

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  • Rickets is a childhood disease in which bones lack calcium and are deformed as a result of vitamin D deficiency (vitamin D helps the body absorb calcium)

  • Rigor mortis is the stiffness that occurs in the body after death

  • Ringworm is a skin infection caused by a fungus that spreads out in an even circle, characterized by ring-like, scaly patches of red skin

  • Rinne's test is a test that uses a tuning fork to diagnose hearing loss resulting from poor conduction of sound from the outer to the inner ear

  • RNA is ribonucleic acid, which helps to decode and process the information contained in DNA

  • Rocky mountain spotted fever is a rare disease transmitted to humans through the bites of ticks; characterized by small pink spots on the wrists and ankles that spread to other parts of the body, become larger, and bleed

  • Rosacea is a skin disorder that is characterized by patches of red skin on the nose and cheeks and acne-like bumps; most commonly occurs in middle-aged women

  • Roseola infantum is a common disease in young children characterized by a sudden fever and rash

  • Rotator cuff is a structure made up of four muscle tendons that reinforces the shoulder joint

  • Roundworm is a group of worms that includes many of the major human parasites

  • Rubella is a mild viral infection (also known as German measles) that produces a rash and fever; dangerous when it infects a woman during the early stages of pregnancy, when it can spread causing birth defects in the fetus

  • Rubeola is another term for measles

  • Rupture is a tear or break in an organ or tissue

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  • Saccharides is a group of carbohydrates, including sugars and starches

  • Sacroiliac joints  is the pair of joints located in the pelvis between the sacrum and the hipbones

  • Sacroiliitis is inflammation of the sacroiliac joints, which causes pain in the lower body

  • Sacrum is the triangular bone located at the bottom of the spine that is connected to the tailbone, the hipbones near the sacroilial joints, and the rest of the spine

  • SADS is see Seasonal affective disorder syndrome

  • Safe sex is measures taken to reduce the risk of acquiring a sexually transmitted disease, such as the use of a condom

  • Saline is a salt solution or any substance that contains salt

  • Salmonella is a group of bacteria; includes a species that causes food poisoning and another responsible for typhoid fever

  • Salpingectomy is surgical removal of one or both fallopian tubes

  • Salpingolysis is removal of abnormal scar tissue between a fallopian tube and nearby tissue

  • Salpingo-oophorectomy is the surgical removal of one or both of the fallopian tubes and one or both of the ovaries

  • Salpingostomy is surgical opening of a fallopian tube for drainage or removal of an obstruction

  • Sarcoidosis is a rare disease with no known cause that leads to inflammation in tissues throughout the body, including the lymph nodes, lungs, liver, skin, and eyes

  • Sarcoma is a cancer in connective tissue, fibrous tissue, or blood vessels

  • Saturated fat is fats that contain the maximum amount of hydrogen possible, such as those found in meats and dairy products; can contribute to coronary heart disease and the development of some cancers

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  • Saturday night palsy is temporary paralysis of the arm after extended pressure on a nerve in the armpit

  • Scabies is a highly contagious skin disorder caused by a mite that burrows into the skin and produces an intense, itchy rash

  • Scarlet fever is an infectious childhood disease, caused by a streptococcus bacteria, that leads to a sore throat, fever, and rash

  • Schistosomiasis is infestation by a parasitic blood worm that can damage the liver, bladder, and intestines

  • Schizophrenia is a group of mental disorders characterized by abnormal thoughts, moods, and actions; sufferers have a distorted sense of reality, and a split personality (thoughts do not logically fit together)

  • Sciatica is pain along the sciatic nerve, which runs down the length of the leg to the foot; usually caused by pressure on the nerve due to disk prolapse or a tumor, abscess, or blood clot

  • Sclera is the tough, white coating that covers and protects the inner structures of the eye

  • Scleroderma is an immune system disorder of varying degree that can affect many areas of the body

  • Sclerotherapy is treatment of varicose veins by injection of a solution that destroys them

  • Scoliosis is a condition in which the spine curves to one side and usually curves toward the opposite side in another section to compensate, producing a characteristic S shape

  • Screening is the testing of an otherwise healthy person in order to diagnose disorders at an early stage

  • Scrotum is the sac containing the testicles

  • Scurvy is a disease caused by a lack of vitamin C, characterized by weakness, bleeding and pain in joints and muscles, bleeding gums, and abnormal bone and tooth growth

  • Sebaceous cyst is a swelling that occurs under the skin, most commonly on the scalp, face, ears, and genitals; although usually harmless, can grow very large and become painful if infected

  • Seborrhea is excessive oiliness of the face and scalp

  • Sebum is the oily, lubricating substance that is secreted by glands in the skin

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  • Secondary is describes a disease or disorder that follows or is caused by another one

  • Sedatives is a group of drugs that have a calming effect; used to treat anxiety and pain, bring on sleep, and help relax a person before surgery

  • Seizure is sudden uncontrolled waves of electrical activity in the brain, causing involuntary movement or loss of consciousness

  • Selenium is an element needed by the body only in very small amounts that helps maintain tissue elasticity

  • Semen is fluid released during ejaculation that contains sperm along with fluids produced by the prostate gland and the seminal vesicles

  • Semen analysis is a procedure in which a semen sample is examined to determine the amount of sperm present, along with their shape and ability to move; commonly used in the treatment of male infertility

  • Seminal vesicles is two saclike glands in men that produce part of the fluid in semen

  • Seminoma is a type of testicular cancer that is made up of only a single type of cell

  • Senile plaques is abnormal deposits of a protein called amyloid in the brain; characteristic of Alzheimer disease

  • Sensorineural hearing loss is deafness caused by damage to the inner ear or the nerve that conducts signals from the ear to the brain

  • Sensory nerve is nerves that carry information about the body’s senses toward the brain

  • Sensory organ is an organ that receives and relays information about the body’s senses to the brain

  • Sepsis is the infection of a wound or tissue with bacteria, causing the spread of the bacteria into the bloodstream; now also known as systemic inflammatory response syndrome caused by a microbe

  • Septal defect is a birth defect in which a hole is present in the wall that separates the left and right sides of the heart

  • Septicemia is a life-threatening condition in which bacteria multiply in the blood and produce toxic materials; commonly known as blood poisoning; now also known as systemic inflammatory response syndrome.

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  • Septic shock is a life-threatening condition in which tissues become damaged and blood pressure drops due to bacteria multiplying and producing poisons in the blood

  • Serotonin is a chemical that transmits nerve impulses in the brain, causes blood vessels to constrict (narrow) at sites of bleeding, and stimulates smooth muscle movement in the intestines

  • Serum is the clear, watery fluid that separates from clotted blood

  • Sex chromosomes is the X and Y chromosomes that determine a person’s gender; women normally have two X chromosomes and men normally have one X and one Y

  • Sex hormones is hormones responsible for producing sex characteristics and controlling sexual functions

  • Shigellosis is a bacterial infection of the intestines, causing abdominal pain and diarrhea

  • Shingles is a nerve infection caused by the chickenpox virus, causing areas of painful rash covered with blisters

  • Shin splints is pain and tenderness experienced in the lower leg as a result of damage or strain to leg muscles and tendons; usually caused by exercise

  • Shock is a reduced flow of blood throughout the body, usually caused by severe bleeding or a weak heart; without treatment, can lead to a collapse, coma, and death

  • Shunt is an artificially constructed or an abnormal passage connecting two usually separate structures in the body

  • Sickle cell anemia is a genetic disorder in which the red blood cells are abnormal and deformed, causing anemia (reduced ability to transport oxygen in the blood) and clogging of blood vessels; bouts of fever, headache, and weakness result

  • Sick sinus syndrome is abnormal functioning of the structure that regulates the heartbeat, causing episodes of abnormal heart rhythm

  • SIDS is see Sudden infant death syndrome

  • Sigmoidoscopy is an examination of the rectum and the lowest part of the large intestine using a flexible viewing tube inserted through the anus

  • Silicone is a group of compounds of silicon and oxygen; commonly used as implants in cosmetic surgery because they resist body fluids and are not rejected by the body

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  • Silicosis is a respiratory disease caused by inhalation of dust containing the mineral silica

  • Single photon emission computed tomography is an imaging technique in which a radioactive substance is introduced into the body and the radiation emitted by the substance is detected by a camera and is transformed into cross-sectional images by a computer

  • Sinoatrial node is the structure that regulates the heartbeat; a natural "pacemaker"

  • Sinus is a cavity within bone or a channel that contains blood; also refers to an abnormal tract in the body

  • Sinusitis is inflammation of the lining of the cavities in the bone surrounding the nose (the sinuses), usually as a result of a bacterial infection spreading from the nose

  • Sjögren's syndrome is a condition characterized by dryness of the eyes, mouth, and vagina that tends to occur along with certain disorders of the immune system

  • Skin graft is a method of treating damaged or lost skin in which a piece of skin is taken from another area of the body and transplanted in a damaged or missing section

  • Skin patch is a sticky patch attached to the surface of the skin that releases drugs into the bloodstream

  • Skin patch test is a diagnostic test in which different allergens are taped to the skin to determine which causes an allergic reaction

  • Skin prick test is a test performed to determine a person’s sensitivity to a certain allergen by applying it to a small needle and using that needle to pierce the skin

  • Skull is the bones that form the framework of the head and enclose and protect the brain and other sensory organs

  • Sleep apnea is a condition in which breathing stops for very short periods of time during sleep

  • Sleeping sickness is an infectious disease in Africa spread by the bite of a tsetse fly that causes a fever and weakness

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  • Small intestine is the long tube running from the stomach to the large intestine that is involved in digestion of foods and absorption of nutrients

  • Smallpox is a highly contagious and often fatal viral infection that has been completely eradicated by immunization

  • Smear is a sample of cells spread across a glass slide to be examined through a microscope

  • Sodium is a mineral that plays a role in the body's water balance, heart rhythm, nerve impulses, and muscle contraction; present in table salt (sodium chloride)

  • Solar plexus is the largest network of nerves in the body, located behind the stomach

  • Spasm is an involuntary muscle contraction; can sometimes be powerful and painful

  • Spasticity is muscle stiffness caused by an increase in contractions of the muscle fibers

  • SPECT is see Single photon emission computed tomography

  • Speculum is an instrument that holds an opening of the body open so that an examination can be performed or a sample can be taken

  • Speech therapy is treatment to help someone overcome a problem communicating verbally

  • Sperm is the male sex cell produced in the testicles

  • Sperm antibody is an antibody against sperm that can be produced by a woman’s immune system

  • Spermatocele is a harmless cyst containing fluid and sperm that occurs in the tube through which sperm travel from the testicles

  • Sperm count is the amount of normally functioning sperm per some unit of semen; used to determine a man's fertility

  • Spermicide is a contraceptive substance that kills sperm

  • Sphincter is a ring of muscle fibers located around a naturally occurring passage or opening in the body that opens and closes to regulate passage of substances

  • Spider nevus is a collection of dilated (widened) capillaries on the skin that creates a patch resembling a spider

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  • Spina bifida is a birth defect in which a section of the baby's spine fails to develop completely, leaving the spinal cord exposed in that section

  • Spina bifida occulta is the least dangerous form of spina bifida, in which bones in the spine fail to close but there is no protrusion of the spinal cord or its fluid cushion out of the body

  • Spinal cord is a long tube of nerve tissue inside the spinal column, running from the brain down the length of the back inside of the spine

  • Spinal fusion is the surgical joining of two or more adjacent vertebrae using bone fragments; used to help severe back pain or prevent damage to the spinal cord

  • Spine is the column of bones and cartilage running along the midline of the back that surrounds and protects the spinal cord and supports the head

  • Spirometry is a test of lung condition; a person breathes into a machine called a spirometer that measures the volume of air exhaled

  • Spleen is an organ located in the upper left abdomen behind the ribs that removes and destroys old red blood cells and helps fight infection

  • Splint is a device that is used to immobilize a part of the body

  • Spondylitis is inflammation of the joints between the bones of the spine

  • Spondylolisthesis is the slipping of a vertebra in the spine over the one below it

  • Spondylolysis is a disorder in which the lower part of the spine is weakened by an abnormally soft vertebra

  • Sporotrichosis is an infection with a fungus acquired through a skin wound; causes an ulcer at the site of infection and small, rounded masses of tissue near it

  • Sprain is the tearing or stretching of the ligaments in a joint, characterized by pain, swelling, and an inability to move the joint

  • Sprue is a digestive disorder in which nutrients cannot be properly absorbed from food, causing weakness and loss of weight

  • Sputum is mucus and other material produced by the lining of the respiratory tract; also called phlegm

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  • Squamous cell carcinoma is a type of skin cancer arising from flat cells of the epithelium; can also affect the lungs, cervix, and esophagus

  • Stapedectomy is surgical removal of a stapes (a sound-conducting bone in the middle ear) that cannot move to transmit sound; performed to treat hearing loss caused by otosclerosis

  • Staphylococci is common bacteria that cause skin infections and a number of other disorders

  • STD is see Sexually transmitted disease

  • Stem cells is cells that give rise to the different types of blood cells

  • Stenosis is narrowing of a body passageway

  • Stent is a device used to hold tissues in place, such as to support a skin graft

  • Stereotaxic surgery is brain surgery done through a small opening in the skull and guided by X-rays or computer-aided imaging techniques

  • Sterilization is a surgery performed to make a person incapable of reproducing; also refers to the process of killing microorganisms on objects such as surgical instruments

  • Sternum is the long, flat bone located at the center of the chest

  • Steroids is a group of drugs that includes corticosteroids, which resemble hormones produced by the adrenal glands, and anabolic steroids, which are similar to the hormones produced by the male sex organs

  • Stillbirth is a baby that is born dead after the 28th week of pregnancy; also called late fetal death

  • Stoma is a surgically formed opening on a body surface

  • Stomach bypass is a surgical procedure to treat an obstructed stomach or severe obesity in which the passage of food is diverted around the stomach and directly into the small intestine

  • Stomach stapling is a procedure in which the stomach is made smaller by partitioning it off using metal staples; used as an extreme treatment of severe obesity

  • Stool is another term for feces

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  • Strabismus is a condition in which the eyes are not aligned correctly, such as cross-eye (one eye points inward) and walleye (one eye points outward)

  • Strain is muscle damage resulting from excessive stretching or forceful contraction

  • Strangulated hernia is a hernia in which the protruding organ or tissue loses its blood supply, requiring emergency surgery

  • Strawberry nevus is a bright red, raised birthmark that usually disappears without treatment

  • Strep throat is a throat infection caused by streptococcus bacteria; characterized by a sore throat, fever, and enlarged lymph nodes in the neck

  • Streptococci is bacteria that cause a variety of diseases, including pneumonia and strep throat

  • Stress fracture is a bone break resulting from repeated pressure on the bone

  • Stretch marks is lines on the skin that occur when the inner skin layer is stretched thin and loses its elasticity

  • Stroke is damage to part of the brain because of a lack of blood supply (due to a blockage in an artery) or the rupturing of a blood vessel; leads to complete or partial loss of function in the area of the body that is controlled by the damaged part of the brain

  • Stye is a pus-filled abscess in the follicle of an eyelash; caused by a bacterial infection

  • Submucosa is the layer of connective tissue under a mucous membrane

  • Sudden infant death syndrome is the unexpected, sudden death of an apparently healthy baby, the cause of which cannot be found; also called crib death

  • Suppository is a solid cone or bullet-shaped object made up of a chemically inactive substance and a drug that is inserted into the rectum or vagina; used to administer a drug

  • Surfactant is a mixture of substances secreted by the air sacs of the lungs that prevents the air sacs from collapsing during exhalation

  • Surrogate is a woman who agrees to become pregnant and give her baby to someone else when the child is born

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  • Suture is a surgical stitch that helps close an incision or wound so that it can heal properly

  • Sweat glands is tiny structures in the skin that secrete sweat

  • Sweat test is a measure of the saltiness of sweat to help diagnose cystic fibrosis

  • Sycosis barbae is a bacterial infection of the hair follicles in the beard area

  • Sympathetic nervous system is the part of the autonomic nervous system that raises blood pressure and heart rate in response to stress

  • Syndactyly is a condition in which fingers or toes are fused together

  • Syndrome is a group of symptoms that indicate a certain disorder when they occur together

  • Synovectomy is surgical removal of the synovial membrane

  • Synovial fluid is a lubricating fluid secreted by the synovial membrane

  • Synovitus is inflammation of the membrane lining a joint capsule as a result of injury or infection or due to a chronic illness such as rheumatoid arthritis; characterized by redness, swelling, stiffness, and pain

  • Syphilis is a sexually transmitted disease; initially causes only painless sores on the genitals but can be life-threatening if untreated

  • Systemic inflammatory response syndrome is a condition characterized by having two of the following four clinical criteria: fever, rapid breathing, increased heart rate, and abnormal white blood cell count

  • Systemic lupus erythematosus is a disease of the immune system that causes inflammation of connective tissue in many areas of the body, including the skin, lungs, heart, joints, and kidneys

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  • Tachycardia is a rapid heart rate (over 100 beats per minute)

  • Tapeworm is a parasitic worm that lives in the intestines; causes diarrhea and abdominal discomfort

  • Tar is the sticky, brown substance in cigarettes that coats the lungs; causes lung and other cancers

  • Tarsorrhaphy is a procedure in which the eyelids are sewn shut; performed to protect the corneas

  • Tartar is the hard deposit formed on teeth when mineral salts in saliva combine with plaque; can cause dental problems such as gum disease if not controlled

  • Tay-Sachs disease is a severe genetic disorder that causes nervous system disturbances and death, usually before the age of 3

  • TB is see Tuberculosis

  • T-cell leukemia is a type of leukemia caused by a virus in which T-lymphocytes divide uncontrollably

  • Tear duct is a tiny passageway that drains lubricating tears from the surface of the eye to the back of the nose

  • Telangiectasia is redness of an area of skin, caused by enlargement and proliferation of the underlying small blood vessels

  • Temperature method is a natural method of family planning in which a woman determines her time of ovulation by changes in her daily temperature

  • Temporal arteritis is inflammation and narrowing of arteries in the head and neck, including those in the scalp near the temple, which can cause blindness if untreated

  • Temporomandibular joint syndrome is headache, facial pain, and jaw tenderness caused by irregularities in the way the joints, muscles, and ligaments in the jaw work together

  • Tendinitis is inflammation of a tendon, usually caused by injury, characterized by pain, tenderness, and sometimes limited movement in the attached muscle

  • Tendon is strong connective tissue cords that attach muscle to bone or muscle to muscle

  • Tendon transfer is surgical cutting and repositioning of a tendon so that the muscle attached to it has a new function

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  • Tennis elbow is a form of tendinitis that causes pain and tenderness in the elbow and forearm

  • Tenosynovitis is inflammation of the inner lining of the sheath that covers a tendon

  • Tenovaginitis is inflammation of the fibrous wall of the sheath that covers a tendon

  • TENS is see Transcutaneous electrical nerve stimulation

  • Tension headache is a headache caused by emotional strain or tension in the muscles of the head and neck

  • Teratogen is anything that causes abnormalities in a developing embryo or fetus, such as a drug or virus

  • Teratoma is a tumor composed of cells not normally found in the part of the body when the tumor occurred

  • Testicles is the two male sex organs that produce sperm and the sex hormone testosterone

  • Testicular feminization factor is a genetic disorder in which an individual who is genetically male has the external appearance of a female because the body is unresponsive to testosterone

  • Testicular torsion is severe pain and swelling of a testicle, due to twisting of the spermatic cord

  • Testosterone is the sex hormone that stimulates development of male sex characteristics and bone and muscle growth; produced by the testicles and in small amounts by the ovaries

  • Tetanus is a sometimes fatal disease affecting the brain and spinal cord; caused by infection with bacterium present in soil and manure

  • Tetracyclines is a group of antibiotic drugs used to treat a wide variety of infections, including bronchitis and some types of pneumonia

  • Tetralogy of Fallot is a genetic heart disease involving four structural defects in the heart, which result in insufficient levels of oxygen in the blood

  • Thalamus is a structure in the brain that relays and processes incoming sensory information from the eyes and ears and from pressure and pain receptors

  • Thalassemia is a group of genetic blood disorders characterized by a defect in the ability to produce hemoglobin, leading to the rupturing of red blood cells (called hemolytic anemia)

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  • Therapeutic range is the range of doses of a drug that will produce beneficial results without side effects

  • Thoracoscopy is examination of the membranes covering the lungs using an endoscope

  • Thoracotomy is a procedure in which the chest is surgically opened to operate on an organ in the chest cavity

  • Thrill is a vibration felt when the hand is placed flat on the chest; caused by abnormal blood flow through the heart as a result of disease

  • Thrombocytopenic purpura is a decrease in the number of platelets in the blood, causing abnormal bleeding of blood vessels into the skin

  • Thromboembolism is blockage of a blood vessel by a blood clot fragment that has broken off and traveled from another area of the body

  • Thrombophlebitis is inflammation of a vein, along with clot formation in the affected area

  • Thrombosis is a condition in which a blood clot (thrombus) has formed inside a blood vessel

  • Thrombus is a blood clot in a blood vessel

  • Thrush is a candidiasis infection

  • Thymoma is a tumor of the thymus gland

  • Thymus gland is an immune system gland located in the upper part of the chest that plays an important role in the production of T-lymphocytes

  • Thyroglossal cyst is a swelling at the front of the neck; forms from a duct that fails to disappear during embryonic development

  • Thyroid gland is a gland located in the front of the neck below the voice box that plays an important role in metabolism (the chemical processes in the body) and growth; the gland produces thyroid hormone

  • Thyrotoxicosis is a toxic condition resulting from overactivity of the thyroid gland

  • Thyroxin is a hormone produced by the thyroid gland that helps regulate energy production in the body

  • TIA is see Transient ischemic attack

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  • Tibia is the thicker of the two long bones in the lower leg; commonly called the shin

  • Tic is an involuntary, repetitive movement such as a twitch

  • Ticks is small, eight-legged animals that can attach to humans and animals and feed on blood; sometimes spread infectious organisms via their bites

  • Tietze's syndrome is inflammation of the cartilage that joins ribs to the breastbone, causing chest pain

  • Tinea is a group of common infections occurring on the skin, hair, and nails that are caused by a fungus; commonly referred to as ringworm

  • Tinnitus is a persistent ringing or buzzing sound in the ear

  • Tipped uterus is an abnormal condition in which the uterus is tilted backward instead of slightly forward

  • Tissue typing is tests used to determine the compatibility of tissues used in grafts and transplants

  • T-lymphocyte is a type of white blood cell that fights infections and destroys abnormal cells directly; as compared with releasing antibodies to fight infection

  • T-lymphocyte killer cell is a type of T-lymphocyte white blood cell that attaches to abnormal cells and releases chemicals that destroy them

  • Tolerance is decreased sensitivity of the body to a certain drug, usually either because the liver becomes more efficient at breaking down the drug or the body's tissues become less sensitive to it; increased tolerance creates a need for a higher dose of the drug in order to have the same effects

  • Tonometry is the procedure used to measure the pressure within the eye; is useful in detecting glaucoma

  • Tonsillectomy is surgical removal of the tonsils, usually to treat tonsillitis

  • Tonsillitis is infection and inflammation of the tonsils

  • Tonsils is masses of lymphoid tissue located at either side of the back of the throat

  • Tourette's syndrome is a movement disorder characterized by involuntary tics and noises, and in some cases uncontrollable shouting of obscenities

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  • Tourniquet is a device placed tightly around an arm or leg in order to stop blood flow; can be used to locate veins in order to take a blood sample or to control blood flow during some operations

  • Toxemia is the presence of bacterial toxins in the blood

  • Toxicity is the extent to which a substance is poisonous

  • Toxin is a poisonous substance

  • Toxocariasis is human infestation with the larvae of a worm found in the intestines of dogs

  • Toxoplasmosis is a common protozoan infection that is usually only dangerous to a fetus in early pregnancy or a person who is immunocompromised

  • TPA is see Tissue plasminogen activator

  • Trachea is the tube running from the larynx (the voice box) down the neck and into the upper part of the chest, where it divides to form the two bronchi of the lungs; commonly called the windpipe

  • Tracheotomy is insertion of a tube through a surgical opening in the trachea to maintain an open airway

  • Trachoma is a persistent, contagious form of conjunctivitis that can lead to complications such as blindness if untreated

  • Traction is the use of tension to hold a body part in place or to correct or prevent an alignment problem

  • Transferrin is a substance in the blood that transports iron throughout the body

  • Transient ischemic attack is a temporary block in the supply of blood to the brain, resulting in temporary loss of sensation, movement, vision, or speech; often called mini- strokes and can be precursors to a real stroke

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  • Transplant is transferring a healthy tissue or organ to replace a damaged tissue or organ; also refers to the tissue or organ transplanted

  • Transurethral prostatectomy is removal of cancerous tissue from the prostate gland using a resectoscope (a long, narrow instrument passed up the urethra), which allows the surgeon to simultaneously view the prostate and cut away the cancerous tissue

  • Trauma is physical injury or emotional shock

  • Travelers' diarrhea is diarrhea when traveling in a foreign country, caused by contaminated food or water

  • Tremor is an involuntary, rhythmic, shaking movement caused by alternating contraction and relaxation of muscles; can be the normal result of age or the abnormal effect of a disorder

  • Triage is a system used to classify sick or injured people according to the severity of their conditions

  • Trichiasis is growth of the eyelashes inward toward the cornea, causing persistent irritation of the eyeball

  • Trichinosis is infestation by the larvae of the parasitic worm Trichinella spiralis, usually acquired by eating undercooked pork

  • Trichomoniasis is infection of the vagina by the single-celled parasite Trichomonas vaginilis, which may cause inflammation, itchiness, and discharge from the vagina

  • Tricuspid valve is the valve located between the two left chambers of the heart (the left atrium and the left ventricle)

  • Trigeminal neuralgia is a disorder of the trigeminal nerve (a cranial nerve) that causes brief attacks of severe pain in the lips, cheeks, gums, or chin on one side of the face

  • Triglyceride is the main form of fat in the blood; determining levels of triglyceride is useful in diagnosing and treating diabetes, high blood pressure, and heart disease

  • Trimester is one of three periods lasting about 3 months each; the stages into which pregnancy is divided

  • Triple X syndrome is the presence of an extra X chromosome in a woman, which may cause some degree of mental retardation

  • Trismus is the medical term for lockjaw

  • Trisomy is the presence in the cells of three copies of a certain chromosome instead of the normal two copies

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  • Tubal ligation is a procedure in which the fallopian tubes are cut and tied off; usually a permanent form of sterilization

  • Tubal pregnancy is a pregnancy that occurs in the fallopian tubes, with a fertilized egg implanting in the tube instead of the uterus; severely painful and can be fatal if not detected and treated

  • Tuberculin test is skin tests performed to determine previous infection with tuberculosis; can help rule out the possibility of being currently infected with tuberculosis

  • Tuberculosis is an infectious bacterial disease transmitted through the air that mainly affects the lungs

  • Tuberous sclerosis is a genetic disorder of the skin and nervous system characterized by epilepsy, mental retardation, and a skin condition resembling acne

  • Tuboplasty is surgical repair of a damaged fallopian tube to treat infertility

  • Tumor is an abnormal mass that occurs when cells in a certain area reproduce unchecked; can be cancerous (malignant) or noncancerous (benign)

  • Tunnel vision is loss of peripheral vision so that only objects directly ahead can be seen; most commonly due to damage caused by increased pressure within the eye (glaucoma)

  • Turner's syndrome is a genetic disorder in women in which only one X chromosome is present, or both chromosomes are present but one is defective

  • Tympanoplasty is a surgical procedure used to treat hearing loss in which the eardrum or structures in the middle ear are repaired

  • Typhoid fever is an acute bacterial infection causing fever, headache, abdominal discomfort, and enlargement of the liver and spleen

  • Typhus is a group of diseases caused by the microorganism rickettsia, spread by the bites of fleas, mites, or ticks; symptoms include headache, fever, rash, and a series of complications if untreated

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  • Ulcer is an open sore that occurs on the skin or on a mucous membrane because of the destruction of surface tissue

  • Ulcerative colitis is a chronic condition in which ulcers occur on the mucous membrane lining of the colon (the end of the large intestine) and the rectum

  • Ultrasound scanning is an imaging procedure used to examine internal organs in which high-frequency sound waves are passed into the body, reflected back, and used to build an image; also sometimes called sonography

  • Ultraviolet light is a form of invisible light in sunlight that is responsible for the tanning and burning of skin and can cause cataracts and skin cancer

  • Umbilical cord is the tubal structure (consisting of two arteries and one vein) that connects the fetus to the placenta, supplying the fetus with oxygen and nutrients and removing some waste products

  • Umbilical hernia is a condition present at birth in which a part of the baby's intestines bulge through a weak area of the abdominal wall, creating a swelling around the navel

  • Unconsciousness is a temporary or prolonged loss of awareness of self and of surroundings

  • Undescended testicle is a testicle that has not moved down from the abdomen, where it develops, into the scrotum

  • Unsaturated fat is a fat or oil found mainly in vegetables; thought to reduce the risk of coronary heart disease

  • Urea is a waste product of the metabolism of proteins that is formed by the liver and secreted by the kidneys

  • Uremia is abnormally high levels of waste products such as urea in the blood

  • Ureters is two tubes that carry urine from the kidneys to the bladder

  • Urethra is the tube by which urine is released from the bladder

  • Urethrocele is a bulging of the urethra into the vagina

  • Urinalysis is a group of physical and chemical tests done on a sample of urine to check for various disorders, including those of the kidneys and urinary tract

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  • Urinary diversion is an operation to allow urine passage when the bladder or urethra has become blocked or been removed

  • Urinary incontinence is the involuntary release of urine because of the inability to control bladder muscles; may occur as a natural part of the aging process or be caused by an injury or disorder

  • Urinary tract is the structures in the body that are responsible for the production and release of urine, including the kidneys, ureters, bladder, and urethra

  • Urticaria is an allergic reaction in which itchy white lumps surrounded by areas of inflammation appear on the skin; commonly called "hives"

  • Uterine prolapse is a condition in which the uterus moves downward into the vagina due to a weakness of the ligaments and muscles that hold the uterus in place

  • Uterus is the hollow female reproductive organ in which a fertilized egg is implanted and a fetus develops

  • Uvea is a structure consisting of the colored area of the eye and the middle layer of the eye that contains blood vessels

  • Uveitis is inflammation of the uvea

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  • Vaccination is a form of immunization in which killed or weakened microorganisms are placed into the body, where antibodies against them are developed; if the same types of microorganisms enter the body again, they will be destroyed by the antibodies

  • Vaccine is a preparation of weakened microorganisms given to create resistance to a certain disease

  • Vacuum extraction is a technique used to facilitate childbirth using a suction device to help move the baby through the birth canal

  • Vagina is the muscular passage connecting the uterus with the outside genitals; a component of the female reproductive system

  • Vaginismus is an involuntary muscle spasm at the opening of the vagina when sexual intercourse is attempted; can be quite painful and may make sexual intercourse nearly impossible

  • Vaginitis is inflammation of the vagina, which can be the result of infection, aging, a hormone deficiency, or a foreign object (such as a tampon)

  • Valve is a structure that allows fluid flow in only one direction

  • Valvotomy is surgical correction of a narrowed heart valve

  • Valvuloplasty is reconstruction or repair of a narrowed heart valve

  • Varicella is the medical term for chickenpox

  • Varices is enlarged or twisted blood or lymph vessels

  • Varicocele is the appearance of varicose veins around the testicles; commonly occurs and is harmless, but may cause discomfort

  • Varicose veins is enlarged, twisted veins just below the surface of the skin, caused by defective valves in the veins

  • Variola is another term for smallpox

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  • Vas deferens is a thin tube that stores and transports sperm

  • Vasectomy is a usually permanent method of sterilization in which the tubes carrying sperm from the testicles (the vas deferens) are cut and tied off; as a result, the semen will no longer contain sperm

  • VD is see Venereal disease

  • Vein is a blood vessel that carries blood toward the heart

  • Venereal disease is any disease that is usually spread through sexual intercourse or genital contact

  • Venipuncture is piercing of a vein with a hollow needle to inject fluid or withdraw blood

  • Venography is an X-ray procedure for viewing veins

  • Venom is a poisonous substance produced by certain animals

  • Ventilation is the process through which oxygen and carbon dioxide are exchanged between the lungs and the air; also refers to the use of a machine to carry out this process in someone who cannot breathe on his or her own

  • Ventilator is a machine used to take over breathing when a person cannot breathe on his or her own

  • Ventricle is a small cavity or chamber; there are four ventricles in the brain that circulate cerebrospinal fluid through it, and two in the heart that pump blood throughout the body

  • Vernix is the thick, greasy substance that covers the skin of a newborn baby

  • Version is a shift in the position of the fetus inside of the uterus, either occurring naturally or as performed by a doctor to facilitate delivery

  • Vertebra is any one of the 33 bones that make up the spine

  • Vertebral arteries is a pair of arteries running up the neck to supply the brain with blood

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  • Vertigo is the feeling that one or one's surroundings are spinning

  • Vesicle is a small skin blister, or any sac in the body, that contains fluid

  • Vestibular glands is two small glands located at the opening of the vagina that secrete a lubricating fluid during sexual stimulation

  • Villi is the millions of fingerlike projections on the lining of the small intestine that aid in the absorption of food

  • Viral is a term describing something related to or caused by a virus

  • Viremia is the presence of viruses in the blood

  • Virilization is the process by which a woman develops male characteristics; caused by overproduction of male sex hormones

  • Virulence is the relative ability of an organism to cause disease

  • Virus is the smallest known disease-causing microorganism; viruses are very simple in structure and can only multiply when they are inside the cell of another organism

  • Visual field is the area on both sides that can be seen while looking straight ahead

  • Vital sign is any sign, such as a pulse, that indicates that a person is alive

  • Vitamin A is a vitamin essential for normal growth and development of the body (most notably the bones and teeth), protection of mucous membranes from infection, normal vision, and healthy skin and hair

  • Vitamin B complex is a group of vitamins including thiamine, niacin, riboflavin, pantothenic acid, pyridoxine, biotin, and folic acid; plays a variety of important roles in the body, including in hormone production, metabolism, and functioning of the nerves, muscle, heart, and digestive system

  • Vitamin B6 is a vitamin that plays an important role in the breakdown and use of energy sources, production of red blood cells and antibodies, and normal functioning of the nervous system

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  • Vitamin B12 is a vitamin that is essential to the production of DNA (the genetic material in cells) and red blood cells and in the functioning of the nervous system

  • Vitamin C is a vitamin with many essential roles, including in maintaining healthy bones, teeth, gums, ligaments, and blood vessels and in the immune system's response to infection

  • Vitamin D is a vitamin that plays a role in the absorption of calcium by the intestines and is essential for healthy bones and teeth

  • Vitamin E is a vitamin that protects tissues from damage by oxygen free radicals, helps to form red blood cells, maintains the function of enzymes, and maintains cell structure

  • Vitamin K is a vitamin that is essential for normal blood clotting and the body's absorption of calcium

  • Vitamins is complex substances that are necessary in small amounts to maintain health and ensure proper development and functioning of the body

  • Vitiligo is a condition in which patches of skin on the body lose their color; thought to be caused by the immune system attacking the skin tissues, causing the absence of melanin

  • Vitreous humor is the clear, watery fluid that fills the cavity of the eye behind the lens

  • VLDL is see Very low-density lipoprotein

  • Vocal cords is two strips of tissue in the voice box that have the ability to produce sound when air passing through them causes the tissues to vibrate

  • Volvulus is twisting and obstruction of an area of intestine

  • V/Q lung scans is images produced by radionuclide scanning of the lungs; used to help diagnose a pulmonary embolism

  • Vulva is the outer, visible portion of the female genitals

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  • Walleye is a condition in which one eye turns outward

  • Wart is a contagious, harmless growth caused by a virus that occurs on the skin or a mucous membrane

  • Weber's test is a test in which a vibrating tuning fork is held against the forehead to help determine the cause of hearing loss

  • Wegener's granulomatosis is a disorder in which nodules associated with inflammation of blood vessels develop in the lungs, kidneys, and nasal passageways

  • Weight-bearing exercise is exercise that puts stress on bones, such as walking, which helps build up bone density and prevent the bones from becoming brittle

  • Wernicke's encephalopathy is a brain disorder characterized by abnormal eye movements, difficulties with muscle coordination, and confusion; usually the result of chronic alcoholism

  • Wheeze is a high-pitched sound produced during breathing because of narrowing of the airways; common sign of asthma

  • Whiplash injury is injury to the ligaments, joints, and soft tissues of the neck region of the spine because of a sudden, violent jerking motion of the head

  • Whipple's disease is a rare disorder that has widespread effects on the body, including impaired absorption of nutrients, weight loss, joint pain, and anemia

  • Whipworm is a small, parasitic worm that can live in the intestines of a human and may cause diarrhea, abdominal pain, and anemia

  • White blood cell is a group of colorless blood cells that are part of the immune system, helping prevent and fight infection

  • White blood cell count is the number of white blood cells present in a blood sample; useful in diagnosing and evaluating various diseases and infections

  • Whitehead is a painless, small, white bump; usually occurs in groups on the nose, cheeks, or around the eyes

  • Whitlow is an abscess on the end of a finger or a toe that is caused by the herpes simplex virus or a bacterial infection

  • Wilm's tumor is a type of kidney cancer that usually affects children under the age of 5

  • Wilson's disease is a rare genetic disorder in which copper builds up in the liver and is released into other parts of the body, eventually causing damage to the liver and brain

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  • Withdrawal bleeding is bleeding from the vagina that occurs when hormone levels drop, such as menstruation or the bleeding that occurs at the end of each cycle of the combined oral contraceptive pill

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  • Xanthelasma is fatty deposits around the eyes that are common in elderly people and are associated with high levels of cholesterol in the blood

  • Xanthine is a bronchodilator drug that is used to treat asthma

  • Xanthomatosis is a condition in which fatty deposits occur in various parts of the body, possibly leading to atherosclerosis

  • X chromosome is one of the two sex chromosomes; determines female sex characteristics

  • Xeroderma pigmentosum is a genetic disorder in which the skin is extremely sensitive to sunlight, causing it to age prematurely and leaving the individual particularly susceptible to skin cancer

  • Xerophthalmia is excessive dryness of the cornea and conjunctiva due to a lack of vitamin A

  • X-linked disorder is a genetic disorder in which the abnormal gene is located on the X chromosome; those affected are almost always men

  • X-ray is see Radiography

  • XYY syndrome is a disorder in which a man has an extra Y chromosome, causing him to be unusually tall and to have behavioral disorders

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  • Y chromosome is one of the two sex chromosomes; determines male sex characteristics

  • Yellow fever is a life-threatening viral infection transmitted by mosquitoes that causes jaundice, fever, headache, and vomiting

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  • ZIFT is see Zygote intrafallopian transfer

  • Zinc chloride is a white powder used as an antiseptic and antiperspirant

  • Zollinger-Ellison syndrome is a rare disorder in which tumors form in the pancreas and secrete the hormone gastrin, which causes increased production of gastric acid and recurrent peptic ulcers

  • Zoonosis is a parasite-caused or infectious disease in animals that can be transferred to humans

  • Zygote is the cell that results when an egg is fertilized by a sperm

  • Zygote intrafallopian transfer is a method used to treat infertility in which an egg fertilized outside the body is placed into a woman's fallopian tube

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