C01-A042

Anatomy of the Human Heart

Diagram of the human heart showing its chambers and major blood vessels.

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 protective sac known as the pericardium, which contains a small amount of fluid to reduce friction. 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 rest of 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 the pulmonary artery.
• Mitral Valve: Located between the left atrium and left ventricle.
• Aortic Valve: Located between the left ventricle and the aorta.

Blood Supply

The heart muscle itself is supplied with blood by the coronary arteries. These arteries branch off from the aorta and encircle the heart, providing oxygen and nutrients to the myocardium.

Electrical Conduction System

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

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 waste products. This is achieved through the coordinated contraction of the heart muscle, known as the cardiac cycle.

Cardiac Cycle

The cardiac cycle consists of two main phases:

• Systole: The phase of contraction, during which the ventricles pump blood out of the heart.
• Diastole: The phase of relaxation, during which the heart chambers fill with blood.

Related Pages

• Cardiovascular system
• Blood pressure
• Electrocardiography
• Heart disease