Kidney: Difference between revisions

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The '''kidneys''' are [[bean]]-shaped [[excretion|excretory]] [[organ (anatomy)|organ]]s in [[vertebrate]]s. Part of the [[urinary system]], the kidneys filter wastes (especially [[urea]]) from the [[blood]] and excrete them, along with [[water (molecule)|water]], as [[human urine|urine]]. The medical field that studies the kidneys and diseases affecting the kidney is called [[nephrology]], from the [[Greek language|Greek]] name for kidney; the [[adjective]] meaning "kidney-related" is '''''renal''''', from [[Latin]].  
[[File:Surface_projections_of_the_organs_of_the_trunk.png|thumb|right|Surface projections of the organs in the trunk, including kidneys]]
[[File:KidneyStructures_PioM.svg|thumb|left|Detailed anatomical structures of the human kidney]]
[[File:Right_kidney_seen_on_abdominal_ultrasound.jpg|thumb|right|Right kidney as seen on abdominal ultrasound]]
[[File:CTscankidney.jpg|thumb|left|CT scan showing a human kidney]]
[[File:Slide42222.JPG|thumb|right|Histological section of kidney tissue under microscope]]
[[File:Slide4nn.JPG|Light microscopy of kidney glomerulus|thumb]]
[[File:Slide5pp.JPG|Kidney histology highlighting tubules|thumb]]
The '''kidneys''' are paired, bean-shaped [[organ (anatomy)|organs]] in the [[vertebrate]] [[urinary system]] responsible for filtering [[blood]] and excreting waste products and excess fluids in the form of [[urine]]. They play a central role in [[homeostasis]], including regulating [[electrolyte]] balance, [[blood pressure]], and [[acid-base balance]]. The study of the kidneys is known as '''[[nephrology]]''' (from Greek ''nephros'' meaning "kidney"), while the term '''renal''' (from Latin ''renes'') is the adjective often used in medical contexts.


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== Anatomy and Location ==
In [[human]]s, the kidneys are located in the [[posterior]] part of the [[abdomen]]. There is one on each side of the [[spine (anatomy)|spine]]; the right kidney sits just below the [[liver]], the left below the [[diaphragm (anatomy)|diaphragm]] and adjacent to the spleen. Above each kidney is an [[adrenal gland]] (also called the ''suprarenal gland'').  The asymmetry within the abdominal cavity caused by the liver results in the right kidney to be slightly lower than the left one.
In humans, the kidneys are located in the posterior portion of the abdominal cavity, one on each side of the [[spine (anatomy)|vertebral column]]. They lie between vertebral levels T12 and L3 and are considered [[retroperitoneal]], meaning they are located behind the [[peritoneum]]. The right kidney typically lies slightly lower than the left to accommodate the overlying [[liver]]. Each kidney is topped by an [[adrenal gland]].


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The kidneys are partially protected by the 11th and 12th pairs of [[ribs]] and are cushioned by a double layer of fat: perirenal and pararenal fat. Rare anatomical variations such as a third kidney may occur.
The kidneys are [[retroperitoneal]], which means they lie behind the [[peritoneum]], the lining of the [[abdominal cavity]]. They are approximately at the [[vertebra]]l level T12 to L3, and the right kidney usually lies slightly lower than the left in order to accommodate the liver.
The upper parts of the kidneys are partially protected by the eleventh and twelfth [[rib]]s, and each whole kidney is surrounded by two layers of fat (the perirenal fat and the pararenal fat) which help to cushion it. In very rare cases, it is possible to have developed three kidneys.


===Organization=== <!--T:4-->
== Structure ==
In a normal [[human]] adult, each kidney is about 11 cm long and about 5 cm thick, weighing 150 [[1 E-1 kg|grams]]. Kidneys weigh about 0.5 percent of a person's total body weight. The kidneys are "bean-shaped" organs, and have a [[concave]] side facing inwards (medially). On this medial aspect of each kidney is an opening, called the [[hilum]], which admits the renal [[artery]], the renal [[vein]], [[nerve]]s, and the [[ureter]].
Each adult kidney is approximately 11 cm long and 5 cm thick, weighing about 150 grams. The kidney has a concave medial border with an opening called the [[renal hilum]], where the [[renal artery]], [[renal vein]], [[ureter]], and nerves enter and exit.


<!--T:5-->
=== Gross anatomy ===
The outer portion of the kidney is called the [[renal cortex]], which sits directly beneath the kidney's [[loose connective tissue|loose connective tissue/fibrous]] [[renal capsule|capsule]]. Deep to the cortex lies the [[renal medulla]], which is divided into 10-20 [[renal pyramid]]s in humans. Each pyramid together with the associated overlying cortex forms a renal lobe. The tip of each pyramid (called a ''[[papilla]]'') empties into a [[calyx]], and the [[calyx (kidney)|calyces]] empty into the [[renal pelvis]]. The pelvis transmits urine to the [[urinary bladder]] via the [[ureter]].
* '''[[Renal capsule]]''' – A tough fibrous layer surrounding the kidney
* '''[[Renal cortex]]''' – The outer layer containing glomeruli and blood vessels
* '''[[Renal medulla]]''' – The inner region organized into cone-shaped [[renal pyramids]]
* '''[[Renal pelvis]]''' – Funnel-shaped structure collecting urine from calyces
* '''[[Ureter]]''' – Tube carrying urine to the bladder
* '''[[Calyx (kidney)|Calyces]]''' – Chambers that collect urine from the pyramids
* '''[[Papilla]]''' – Tip of each renal pyramid that empties into a calyx


===Blood supply=== <!--T:6-->
== Blood Supply ==
Each kidney receives its [[renal circulation|blood supply]] from the [[renal artery]], two of which branch from the abdominal [[aorta]]. Upon entering the hilum of the kidney, the renal artery divides into smaller interlobar arteries situated between the renal papillae. At the outer medulla, the interlobar arteries branch into arcuate arteries, which course along the border between the renal medulla and cortex, giving off still smaller branches, the cortical radial arteries (sometimes called ''interlobular arteries''). Branching off these cortical arteries are the afferent arterioles supplying the glomerular capillaries, which drain into efferent arterioles. Efferent arterioles divide into peritubular capillaries that provide an extensive blood supply to the cortex. Blood from these capillaries collects in renal venules and leaves the kidney via the [[renal vein]]. Efferent arterioles of glomeruli closest to the medulla (those that belong to [[juxtamedullary nephron]]s) send branches into the medulla, forming the vasa recta. Blood supply is intimately  linked to blood pressure.
The kidneys receive about 20–25% of the cardiac output through the [[renal artery]], a direct branch of the [[abdominal aorta]]. The renal artery branches into:
* Interlobar arteries → Arcuate arteries → Interlobular (cortical radial) arteries
* Afferent arterioles → [[Glomerulus]] → Efferent arterioles
* Peritubular capillaries and vasa recta


===Nephron=== <!--T:7-->
Filtered blood exits through the [[renal vein]] into the [[inferior vena cava]].


<!--T:8-->
== Nephron ==
{{main|Nephron}}
{{main|Nephron}}
The basic functional unit of the kidney is the [[nephron]], of which there are more than a million within the cortex and medulla of each normal adult human kidney. Nephrons regulate water and soluble matter (especially [[electrolyte]]s) in the body by first filtering the blood under pressure, and then reabsorbing some necessary fluid and molecules back into the blood while secreting other, unneeded molecules. Reabsorption and secretion are accomplished with both cotransport and [[countercurrent exchange|countertransport]] mechanisms established in the nephrons and associated collecting ducts.


===Collecting duct system=== <!--T:9-->
Each kidney contains over a million nephrons – the microscopic functional units. Each nephron consists of:
{{main|Collecting duct system}}
* [[Glomerulus]] – site of filtration
The fluid flows from the nephron into the [[collecting duct system]]. This segment of the nephron is crucial to the process of water conservation by the organism. In the presence of [[antidiuretic hormone]] (ADH; also called vasopressin), these ducts become permeable to water and facilitate its reabsorption, thus concentrating the urine and reducing its volume. Conversely, when the organism must eliminate excess water, such as after excess fluid drinking, the production of ADH is decreased and the collecting tubule becomes less permeable to water, rendering urine dilute and abundant. Failure of the organism to decrease ADH production appropriately may lead to water retention and dangerous dilution of body fluids, which in turn may cause severe neurological damage.  Failure to produce ADH (or inability of the collecting ducts to respond to it) may cause excessive urination, called [[diabetes insipidus]].
* [[Bowman's capsule]]
* [[Proximal convoluted tubule]]
* [[Loop of Henle]]
* [[Distal convoluted tubule]]
* [[Collecting duct system]]


<!--T:10-->
Processes:
After being processed along the collecting tubules and ducts, the fluid, now called [[urine]], is drained into the [[urinary bladder|bladder]] via the [[ureter]], to be finally excluded from the organism.
* '''Filtration''' of blood plasma
* '''Reabsorption''' of vital substances (e.g., glucose, Na⁺)
* '''Secretion''' of waste (e.g., H⁺, drugs)
* '''Excretion''' as urine


==Functions== <!--T:11-->
== Collecting Duct System ==
The kidneys are sophisticated reprocessing machines. Every day, your kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water. The waste and extra water become urine, which flows to your bladder through tubes called ureters. Your bladder stores urine until you go to the bathroom.
{{main|Collecting duct system}}


<!--T:12-->
The collecting ducts transport urine through the [[renal medulla]] to the [[renal pelvis]]. [[Antidiuretic hormone]] (ADH) regulates water permeability:
The wastes in your [[blood]] come from the normal breakdown of active tissues and from the food you eat. Your body uses the food for energy and self-repair. After your body has taken what it needs from the food, waste is sent to the blood. If your kidneys did not remove these wastes, the wastes would build up in the blood and damage your body.
* ↑ADH = concentrated urine
* ↓ADH = dilute urine


<!--T:13-->
Deficiency or resistance to ADH can result in [[diabetes insipidus]].
The actual filtering occurs in tiny units inside your kidneys called nephrons. Every kidney has about a million [[nephrons]]. In the nephron, a glomerulus—which is a tiny blood vessel, or capillary—intertwines with a tiny urine-collecting tube called a tubule. A complicated chemical exchange takes place, as waste materials and water leave your blood and enter your urinary system.


<!--T:14-->
== Physiological Functions ==
At first, the tubules receive a combination of waste materials and chemicals that your body can still use. Your kidneys measure out chemicals like sodium, phosphorus, and potassium and release them back to the blood to return to the body. In this way, your kidneys regulate the body’s level of these substances. The right balance is necessary for life, but excess levels can be harmful.
The kidneys filter roughly 180 liters of blood daily, forming 1.5–2 liters of urine. Functions include:


<!--T:15-->
=== Waste Excretion ===
In the nephron, tiny blood vessels intertwine with urine-collecting tubes. Each kidney contains about 1 million nephrons.
Removal of nitrogenous waste:
* [[Urea]]
* [[Uric acid]]
* [[Creatinine]]


<!--T:16-->
=== Electrolyte and Fluid Balance ===
In addition to removing wastes, your kidneys release three important hormones:
Regulation of:
* Sodium (Na⁺)
* Potassium (K⁺)
* Calcium (Ca²⁺)
* Phosphate
* Water balance


<!--T:17-->
=== Acid-Base Balance ===
[[erythropoietin]] (eh-RITH-ro-POY-eh-tin), or EPO, which stimulates the bone marrow to make red blood cells
Maintenance of blood pH (~7.4) by:
* H⁺ excretion
* HCO₃⁻ reabsorption


<!--T:18-->
Main transporters:
[[renin]] (REE-nin), which regulates blood pressure
* [[NHE3]], [[H⁺-ATPase]], [[NBC1]], [[AE1]]


<!--T:19-->
=== Blood Pressure Regulation ===
[[calcitriol]] (kal-suh-TRY-ul), the active form of vitamin D, which helps maintain calcium for bones and for normal chemical balance in the body
Via the [[Renin–angiotensin–aldosterone system]] (RAAS):
* ↓Blood pressure → ↑[[Renin]] → ↑Angiotensin II → ↑[[Aldosterone]] → Na⁺ retention → ↑Blood volume → ↑Blood pressure


===Excretion of waste products=== <!--T:20-->
=== Hormone Secretion ===
The kidneys excrete a variety of [[waste products]] produced by [[metabolism]], including the nitrogenous wastes: [[urea]] (from protein catabolism) and [[uric acid]] (from nucleic acid metabolism).
* '''[[Erythropoietin]]''' – stimulates red blood cell production
* '''[[Renin]]''' – blood pressure regulation
* '''[[Calcitriol]]''' – active vitamin D for calcium homeostasis


===Homeostasis=== <!--T:21-->
== Medical Terminology ==
'''Acid-Base Balance'''
* ''Nephro-'' (Greek) and ''Renal-'' (Latin) denote kidney-related terms
* [[Nephrectomy]] = surgical removal of a kidney
* [[Radical nephrectomy]] = removal of the kidney with surrounding structures


<!--T:22-->
== Diseases and Disorders ==
The kidneys regulate the [[pH]], mineral ion concentration, and water composition of the blood.
=== Congenital ===
* [[Polycystic kidney disease]]
* [[Horseshoe kidney]]
* [[Renal dysplasia]]
* [[Congenital hydronephrosis]]
* [[Duplicated ureter]]


<!--T:23-->
=== Acquired ===
By exchanging [[hydronium ions]] and [[hydroxyl|hydroxyl ions]], the blood plasma is maintained by the kidney at a neutral pH 7.4. Urine, on the other hand, is acidic at pH 5 or alkaline at pH 8.
* [[Glomerulonephritis]]
* [[Nephrotic syndrome]]
* [[Pyelonephritis]]
* [[Diabetic nephropathy]]
* [[Kidney stones]]
* [[Renal cell carcinoma]]
* [[Lupus nephritis]]
* [[Minimal change disease]]
* [[Renal failure]] (acute or chronic)


<!--T:24-->
== Chronic Kidney Disease (CKD) Staging ==
The pH is maintained through four main [[protein]] transporters: NHE3 (a [[sodium]]-[[hydrogen]] exchanger), V-type H-ATPase (an [[isoform]] of the hydrogen ATPase), NBC1 (a sodium-[[bicarbonate]] cotransporter) and AE1 (an [[anion]] exchanger which exchanges chloride for bicarbonate). Due to the polar alignment of cells in the renal epithelia NHE3 and the H-ATPase are exposed to the [[lumen]] (which is essentially outside the body), on the [[apical]] side of the cells, and are responsible for excreting hydrogen ions (or protons). Conversely, NBC1 and AE1 are on the [[basolateral]] side of the cells, and allow bicarbonate ions to move back into the extracellular fluid and thus are returned to the blood plasma.
CKD is staged by [[glomerular filtration rate]] (GFR):
* '''Stage 1''': Normal GFR (>90), kidney damage
* '''Stage 2''': GFR 60–89
* '''Stage 3''': GFR 30–59, moderate dysfunction
* '''Stage 4''': GFR 15–29, severe damage
* '''Stage 5''': GFR <15, [[End-stage renal disease]] (ESRD), requires dialysis or transplant


<!--T:25-->
== Dialysis and Transplantation ==
'''Blood Pressure'''
* [[Dialysis]] removes waste via machine (hemodialysis) or abdominal lining (peritoneal dialysis)
* [[Kidney transplantation]] offers a curative option
** First successful transplant: 1954, Boston
** Types: [[Living donor]] and [[Deceased donor]]
* Immunosuppressive therapy is required post-transplant


<!--T:26-->
== Gallery ==
Sodium ions are controlled in a homeostatic process involving [[aldosterone]] which increases sodium ion absorption in the distal convoluted tubules.
<gallery>
 
File:Left_kidney.jpg|Posterior view of the left kidney
<!--T:27-->
File:Kidney_Nephron.png|Schematic of a kidney nephron
When blood pressure becomes low, a hormone called [[Renin]] is secreted by cells of the juxtaglomerular apparatus (part of the distal convoluted tubule) which are sensitive to pressure. Renin acts on a blood protein, angiotensinogen, converting it to angiotensin. Angiotensin stimulates the secretion of Aldosterone by the adrenal cortex, which affects the kidney tubules.
File:Physiology_of_Nephron.png|Diagram showing nephron function
 
File:2618_Nephron_Secretion_Reabsorption.jpg|Mechanism of secretion and reabsorption in nephrons
<!--T:28-->
File:Peritoneal_dialysis.jpg|Diagram of peritoneal dialysis setup
Aldosterone stimulates an increase in the reabsorption of sodium ions from the kidney tubules which causes an increase in the volume of water that is reabsorbed from the tubule. This increase in water reabsorption increases the volume of blood which ultimately raises the blood pressure.
</gallery>
 
<!--T:29-->
'''Plasma Volume'''
 
<!--T:30-->
Any rise or drop in blood osmotic pressure due to a lack or excess of water is detected by the [[hypothalamus]], which notifies the [[pituitary gland]] via [[negative feedback]]. A lack of water causes the [[posterior pituitary gland]] to secrete [[antidiuretic hormone]], which results in water reabsorption and an increase in urine concentration. Tissue fluid concentration thus returns to a mean of 98%.
 
===Hormone secretion=== <!--T:31-->
The kidneys secrete a variety of [[hormone]]s, including [[erythropoietin]], [[urodilatin]] and [[vitamin D]].
 
==Terms== <!--T:32-->
*'''[[renal capsule]]''': The membranous covering of the kidney.
*'''[[cortex (anatomy)|cortex]]''': The outer layer over the internal medulla. It contains blood vessels, glomeruli (which are the kidneys' "filters") and [[urine]] tubes and is supported by a fibrous matrix.
*'''[[hilus]]''': The opening in the middle of the concave medial border for nerves and blood vessels to pass into the renal sinus.
*'''[[renal column]]''': The structures which support the cortex. They consist of lines of blood vessels and urinary tubes and a fibrous material.
*'''[[renal sinus]]''': The cavity which houses the renal pyramids.
*'''[[calyx (kidney)|calyces]]''': The recesses in the internal medulla which hold the pyramids. They are used to subdivide the sections of the kidney. (singular - ''calyx'')
*'''[[papillae]]''': The small conical projections along the wall of the [[renal sinus]]. They have openings through which urine passes into the calyces. (singular - [[papilla]])
*'''[[renal pyramids]]''': The conical segments within the internal medulla. They contain the secreting apparatus and tubules and are also called ''[[malpighian pyramid]]s''.
*'''[[renal artery]]''': Two renal arteries come from the [[aorta]], each connecting to a kidney. The artery divides into five branches, each of which leads to a ball of capillaries. The arteries supply (unfiltered) blood to the kidneys. The left kidney receives about 60% of the renal bloodflow.
*'''[[renal vein]]''': The filtered blood returns to circulation through the renal veins which join into the [[inferior vena cava]].
*'''[[renal pelvis]]''': Basically just a [[funnel]], the renal pelvis accepts the urine and channels it out of the hilus into the [[ureter]].
*'''[[ureter]]''': A narrow tube 40 cm long and 4 mm in diameter. Passing from the renal pelvis out of the hilus and down to the [[urinary bladder|bladder]]. The ureter carries urine from the kidneys to the [[urinary bladder|bladder]] by means of [[peristalsis]].
 
==Diseases and disorders== <!--T:33-->
===Congenital===
 
<!--T:34-->
*[[Congenital hydronephrosis]]
*[[Congenital obstruction of urinary tract]]
*[[Duplicated ureter]]
*[[Horseshoe kidney]]
*[[Polycystic kidney disease]]
*[[Renal dysplasia]]
*[[Unilateral small kidney]]
 
===Acquired=== <!--T:35-->
*[[Azotemia]] is a toxic condition characterized by abnormal and dangerously high levels of urea, creatinine, various body waste compounds, and other nitrogen-rich compounds in the blood.
*[[Diabetic nephropathy]]
*[[Glomerulonephritis]]
*[[Hydronephrosis]] is the enlargement of one or both of the kidneys caused by obstruction of the flow of urine.
*[[Interstitial nephritis]]
 
<!--T:36-->
*[[Kidney stone]]s are a relatively common and particularly painful disorder.
*Kidney tumors
**[[Wilms tumor]]
**[[Renal cell carcinoma]]
*[[Lupus nephritis]]
*[[Minimal change disease]]
*In [[nephrotic syndrome]], the [[glomerulus (kidney)|glomerulus]] has been damaged so that a large amount of [[protein]] in the blood enters the [[urine]]. Other frequent features of the nephrotic syndrome include swelling, low serum albumin, and high cholesterol.
*[[Pyelonephritis]] is infection of the kidneys and is frequently caused by complication of a [[urinary tract infection]].
*[[Renal failure]]
** [[Acute renal failure]]
 
==Stages of kidney disease== <!--T:37-->
The GFR is the best indicator of how well the kidneys are working. In 2002, the National Kidney Foundation published treatment guidelines that identified five stages of CKD based on declining GFR measurements. The guidelines recommend different actions based on the stage of kidney disease.
 
<!--T:38-->
Increased risk of CKD. A GFR of 90 or above is considered normal. Even with a normal GFR, you may be at increased risk for developing CKD if you have diabetes, high blood pressure, or a family history of kidney disease. The risk increases with age: People over 65 are more than twice as likely to develop CKD as people between the ages of 45 and 65. African Americans also have a higher risk of developing CKD.
 
<!--T:39-->
'''Stage 1:''' Kidney damage with normal GFR (90 or above). Kidney damage may be detected before the GFR begins to decline. In this first stage of kidney disease, the goals of treatment are to slow the progression of CKD and reduce the risk of heart and blood vessel disease.
 
<!--T:40-->
'''Stage 2:''' Kidney damage with mild decrease in GFR (60 to 89). When kidney function starts to decline, your health care provider will estimate the progression of your CKD and continue treatment to reduce the risk of other health problems.
 
<!--T:41-->
'''Stage 3:''' Moderate decrease in GFR (30 to 59). When CKD has advanced to this stage, anemia and bone problems become more common. Work with your health care provider to prevent or treat these complications.
 
<!--T:42-->
'''Stage 4:''' Severe reduction in GFR (15 to 29). Continue following the treatment for complications of CKD and learn as much as you can about the treatments for kidney failure. Each treatment requires preparation. If you choose hemodialysis, you will need to have a procedure to make a vein in your arm larger and stronger for repeated needle insertions. For peritoneal dialysis, you will need to have a catheter placed in your abdomen. Or you may want to ask family or friends to consider donating a kidney for transplantation.
 
<!--T:43-->
'''Stage 5''': Kidney failure (GFR less than 15). When the kidneys do not work well enough to maintain life, you will need dialysis or a kidney transplant.
 
In addition to tracking your GFR, blood tests can show when substances in your blood are out of balance. If phosphorus or potassium levels start to climb, a blood test will prompt your health care provider to address these issues before they permanently affect your health.
 
** [[Chronic renal failure]]
*[[Trauma]]
 
==Dialysis and kidney transplants== <!--T:46-->
Generally, humans can live normally with just one kidney. Only when the amount of functioning kidney tissue is greatly diminished will [[renal failure]] develop. If [[renal function]] is impaired, various forms of [[medication]]s are used, while others are [[contraindicated]]. Provided that treatment is begun early, it may be possible to reverse chronic kidney failure due to diabetes or high blood pressure. If [[creatinine clearance]] (a measure of renal function) has fallen very low ("end-stage renal failure"), or if the renal dysfunction leads to severe symptoms, [[dialysis]] is commenced. Dialysis is a medical procedure, performed in various different forms, where the blood is filtered outside of the body.
 
<!--T:47-->
[[Kidney transplantation]] is the only cure for end stage renal failure; dialysis, is a supportive treatment; a form of "buying time" to bridge the inevitable wait for a suitable organ.
 
<!--T:48-->
The first successful kidney transplant was announced on [[March 4]], [[1954]] at [[Peter Bent Brigham Hospital]] in [[Boston, Massachusetts|Boston]]. The surgery was performed by Dr. [[Joseph E. Murray]], who was awarded the [[Nobel Prize|Nobel Prize in Medicine]] in 1990 for this feat.
 
<!--T:49-->
There are two types of kidney transplants: living donor transplant and a cadaveric (dead donor) transplant. When a kidney from a living donor, usually a blood relative, is transplanted into the patient's body, the donor's blood group and tissue type must be judged compatible with the patient's, and extensive medical tests are done to determine the health of the donor. Before a cadaveric donor's organs can be transplanted, a series of medical tests have to be done to determine if the organs are healthy. Also, in some countries, the family of the donor must give its consent for the [[organ donation]]. In both cases, the recipient of the new organ needs to take drugs to suppress their [[immune system]] to help prevent their body from rejecting the new kidney [http://www.mayoclinic.org/kidney-transplant/livingdonor.html].


==Medical terminology== <!--T:50-->
== See Also ==
* Medical terms related to the kidneys involve the prefixes ''renal-'' and ''nephro-''.
* [[Urology]]
* Surgical removal of the kidney is a ''[[nephrectomy]]'', while a ''radical nephrectomy'' is removal of the kidney, its surrounding tissue, lymph nodes, and potentially the adrenal gland. A radical nephrectomy is performed for the removal of [[cancer]]s.
* [[Nephrology]]
* [[Urinary system]]
* [[Kidney development]]
* [[Endocrine system]]
* [[Kidney transplantation]]
* [[Glomerular filtration rate]]


==See also==
*[[Urology]]
*[[Nephrology]]
*[[Nephropathy]]
*[[Human anatomy]]
*[[Kidney development]]
{{stub}}
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[[Category:Organs]]
[[Category:Organs]]
[[Category:Abdomen]]
[[Category:Abdomen]]
[[Category:Urinary system]]
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[[Category:Kidney]]
<gallery>
File:Surface_projections_of_the_organs_of_the_trunk.png|Kidney
File:KidneyStructures_PioM.svg|Kidney
File:Right_kidney_seen_on_abdominal_ultrasound.jpg|Kidney
File:CTscankidney.jpg|Kidney
File:Slide42222.JPG|Kidney
File:Left_kidney.jpg|Kidney
File:Kidney_Nephron.png|Kidney
File:Physiology_of_Nephron.png|Kidney
File:2618_Nephron_Secretion_Reabsorption.jpg|Kidney
File:Peritoneal_dialysis.jpg|Kidney
File:Slide4nn.JPG|Kidney
File:Slide5pp.JPG|Kidney
</gallery>
<gallery>
File:Blausen 0592 KidneyAnatomy 01.png|Kidney Anatomy
File:Diagram showing the position of the adrenal glands CRUK 343.svg|Position of the Adrenal Glands
</gallery>

Latest revision as of 19:40, 21 March 2025

Surface projections of the organs in the trunk, including kidneys
Detailed anatomical structures of the human kidney
Right kidney as seen on abdominal ultrasound
CT scan showing a human kidney
Histological section of kidney tissue under microscope
Light microscopy of kidney glomerulus
Kidney histology highlighting tubules

The kidneys are paired, bean-shaped organs in the vertebrate urinary system responsible for filtering blood and excreting waste products and excess fluids in the form of urine. They play a central role in homeostasis, including regulating electrolyte balance, blood pressure, and acid-base balance. The study of the kidneys is known as nephrology (from Greek nephros meaning "kidney"), while the term renal (from Latin renes) is the adjective often used in medical contexts.

Anatomy and Location[edit]

In humans, the kidneys are located in the posterior portion of the abdominal cavity, one on each side of the vertebral column. They lie between vertebral levels T12 and L3 and are considered retroperitoneal, meaning they are located behind the peritoneum. The right kidney typically lies slightly lower than the left to accommodate the overlying liver. Each kidney is topped by an adrenal gland.

The kidneys are partially protected by the 11th and 12th pairs of ribs and are cushioned by a double layer of fat: perirenal and pararenal fat. Rare anatomical variations such as a third kidney may occur.

Structure[edit]

Each adult kidney is approximately 11 cm long and 5 cm thick, weighing about 150 grams. The kidney has a concave medial border with an opening called the renal hilum, where the renal artery, renal vein, ureter, and nerves enter and exit.

Gross anatomy[edit]

  • Renal capsule – A tough fibrous layer surrounding the kidney
  • Renal cortex – The outer layer containing glomeruli and blood vessels
  • Renal medulla – The inner region organized into cone-shaped renal pyramids
  • Renal pelvis – Funnel-shaped structure collecting urine from calyces
  • Ureter – Tube carrying urine to the bladder
  • Calyces – Chambers that collect urine from the pyramids
  • Papilla – Tip of each renal pyramid that empties into a calyx

Blood Supply[edit]

The kidneys receive about 20–25% of the cardiac output through the renal artery, a direct branch of the abdominal aorta. The renal artery branches into:

  • Interlobar arteries → Arcuate arteries → Interlobular (cortical radial) arteries
  • Afferent arterioles → Glomerulus → Efferent arterioles
  • Peritubular capillaries and vasa recta

Filtered blood exits through the renal vein into the inferior vena cava.

Nephron[edit]

Main article: Nephron

Each kidney contains over a million nephrons – the microscopic functional units. Each nephron consists of:

Processes:

  • Filtration of blood plasma
  • Reabsorption of vital substances (e.g., glucose, Na⁺)
  • Secretion of waste (e.g., H⁺, drugs)
  • Excretion as urine

Collecting Duct System[edit]

Main article: Collecting duct system

The collecting ducts transport urine through the renal medulla to the renal pelvis. Antidiuretic hormone (ADH) regulates water permeability:

  • ↑ADH = concentrated urine
  • ↓ADH = dilute urine

Deficiency or resistance to ADH can result in diabetes insipidus.

Physiological Functions[edit]

The kidneys filter roughly 180 liters of blood daily, forming 1.5–2 liters of urine. Functions include:

Waste Excretion[edit]

Removal of nitrogenous waste:

Electrolyte and Fluid Balance[edit]

Regulation of:

  • Sodium (Na⁺)
  • Potassium (K⁺)
  • Calcium (Ca²⁺)
  • Phosphate
  • Water balance

Acid-Base Balance[edit]

Maintenance of blood pH (~7.4) by:

  • H⁺ excretion
  • HCO₃⁻ reabsorption

Main transporters:

Blood Pressure Regulation[edit]

Via the Renin–angiotensin–aldosterone system (RAAS):

  • ↓Blood pressure → ↑Renin → ↑Angiotensin II → ↑Aldosterone → Na⁺ retention → ↑Blood volume → ↑Blood pressure

Hormone Secretion[edit]

  • Erythropoietin – stimulates red blood cell production
  • Renin – blood pressure regulation
  • Calcitriol – active vitamin D for calcium homeostasis

Medical Terminology[edit]

  • Nephro- (Greek) and Renal- (Latin) denote kidney-related terms
  • Nephrectomy = surgical removal of a kidney
  • Radical nephrectomy = removal of the kidney with surrounding structures

Diseases and Disorders[edit]

Congenital[edit]

Acquired[edit]

Chronic Kidney Disease (CKD) Staging[edit]

CKD is staged by glomerular filtration rate (GFR):

  • Stage 1: Normal GFR (>90), kidney damage
  • Stage 2: GFR 60–89
  • Stage 3: GFR 30–59, moderate dysfunction
  • Stage 4: GFR 15–29, severe damage
  • Stage 5: GFR <15, End-stage renal disease (ESRD), requires dialysis or transplant

Dialysis and Transplantation[edit]

Gallery[edit]

  • Posterior view of the left kidney
    Posterior view of the left kidney
  • Schematic of a kidney nephron
    Schematic of a kidney nephron
  • Diagram showing nephron function
    Diagram showing nephron function
  • Mechanism of secretion and reabsorption in nephrons
    Mechanism of secretion and reabsorption in nephrons
  • Diagram of peritoneal dialysis setup
    Diagram of peritoneal dialysis setup

See Also[edit]

Urinary system - Kidney - edit
Renal capsule | Renal cortex | Renal medulla (Renal sinus, Renal pyramids) | Renal calyx | Renal pelvis
Nephron - Renal corpuscle (Glomerulus, Bowman's capsule) → Proximal tubule → Loop of Henle → Distal convoluted tubule → Collecting ducts

Juxtaglomerular apparatus (Macula densa, Juxtaglomerular cells)

Renal circulation - Renal artery → Interlobar arteries → Arcuate arteries → Cortical radial arteries → Afferent arterioles → Glomerulus → Efferent arterioles → Vasa recta → Arcuate vein → Renal vein

Renal physiology
Filtration - Ultrafiltration | Countercurrent exchange

Hormones effecting filtration - Antidiuretic hormone (ADH) | Aldosterone | Atrial natriuretic peptide

Endocrine - Renin | Erythropoietin (EPO) | Calcitriol (Active vitamin D) | Prostaglandins

Assessing Renal function / Measures of Dialysis
Glomerular filtration rate | Creatinine clearance | Renal clearance ratio | Urea reduction ratio | Kt/V | Standardized Kt/V | Hemodialysis product
Anatomy of the urinary system
Kidneys
Ureters
Bladder
Urethra


Diseases of the endocrine system (E00–E35, 240–259)
Pancreas/
glucose
metabolism
Hypothalamic/
pituitary axes
Hypothalamus
Pituitary
Thyroid
Parathyroid
Adrenal
Height
Multiple
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