Heart Anatomy and Function

Structure and Location

The heart is a hollow, muscular organ about the size of a clenched fist. It's located in the chest cavity, between the lungs, within the mediastinum. Its shape resembles a triangular pyramid with a base and upper left and lower right edges. The heart is enclosed by the pericardium, a double-layered sac. The outer layer is fibrous, while the inner layer is the serous pericardium. Pericardial fluid between these layers lubricates the heart's movement.

Chambers and Valves

Internally, the heart has four chambers: two atria and two ventricles. The atria, located superiorly, have thin walls. The ventricles, situated inferiorly, have thicker walls (approximately 4mm). The right ventricle's wall is about 0.5cm thick, while the left ventricle's wall is around 1cm thick. A septum separates the right and left sides of the heart, preventing blood from mixing between the two atria and the two ventricles. Blood flows from the right atrium to the right ventricle and from the left atrium to the left ventricle.

Blood Flow and Circulation

The thin-walled atria receive blood passively. The right atrium receives deoxygenated blood from the body through the superior vena cava (carrying blood from the upper body) and the inferior vena cava (carrying blood from the lower body). It also receives blood from the heart itself via the coronary veins. This deoxygenated blood then flows into the right ventricle through the right atrioventricular orifice, which contains the tricuspid valve. The tricuspid valve prevents blood from flowing back into the atrium. From the right ventricle, blood is pumped into the pulmonary artery (the only artery carrying deoxygenated blood) and travels to the lungs. In the lungs, gas exchange (hematosis) occurs, where carbon dioxide is removed from the blood, and oxygen is absorbed. Oxygenated blood returns to the heart's left atrium through four pulmonary veins (the only veins carrying oxygenated blood). The blood then flows into the left ventricle through the left atrioventricular orifice, which contains the bicuspid (mitral) valve. Finally, the oxygen-rich blood is pumped from the left ventricle into the aorta, the body's main artery, and is distributed throughout the body. The difference in the thickness of the ventricles' walls reflects their respective functions: the right ventricle pumps blood to the lungs, while the left ventricle pumps blood to the entire body. Both the pulmonary artery and the aorta contain semilunar valves (pulmonary and aortic, respectively) that prevent blood from flowing backward.