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Anatomy of the Human Heart

Diagram of the human heart

The human heart is a muscular organ responsible for pumping blood through the circulatory system. It is located in the thoracic cavity, between the lungs, and is roughly the size of a fist. The heart is composed of four chambers: two upper chambers called the atria and two lower chambers called the ventricles.

Structure

The heart is enclosed in a double-walled sac called the pericardium, which provides protection and lubrication. The heart wall itself is composed of three layers: the outer epicardium, the middle myocardium, and the inner endocardium.

Chambers

The heart's four chambers are:

• Right Atrium: Receives deoxygenated blood from the body through the superior vena cava and inferior vena cava.
• Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.
• Left Atrium: Receives oxygenated blood from the lungs through the pulmonary veins.
• Left Ventricle: Pumps oxygenated blood to the body through the aorta.

Valves

The heart contains four main valves that ensure unidirectional blood flow:

• Tricuspid Valve: Located between the right atrium and right ventricle.
• Pulmonary Valve: Located between the right ventricle and pulmonary artery.
• Mitral Valve: Located between the left atrium and left ventricle.
• Aortic Valve: Located between the left ventricle and aorta.

Function

The primary function of the heart is to maintain a continuous flow of blood throughout the body, delivering oxygen and nutrients to tissues and removing carbon dioxide and other wastes. This is achieved through the cardiac cycle, which consists of two main phases: systole and diastole.

Cardiac Cycle

• Systole: The phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries.
• Diastole: The phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood.

Blood Supply

The heart itself requires a constant supply of oxygen-rich blood, which is provided by the coronary arteries. These arteries branch off from the aorta and encircle the heart muscle.

Electrical Conduction System

The heart's rhythmic contractions are controlled by an electrical conduction system, which includes the sinoatrial node (SA node), atrioventricular node (AV node), bundle of His, and Purkinje fibers. The SA node, located in the right atrium, acts as the natural pacemaker of the heart.

Related Pages

• Cardiovascular system
• Blood pressure
• Electrocardiography
• Heart disease