The heart, a muscular powerhouse, pumps blood through our bodies. It's divided into four chambers: two on top and two below. These work together to move blood through the pulmonary and systemic circulations.
The heart's structure is key to its function. Layers like the , , and protect and power the heart. ensure blood flows in the right direction, while the feed the heart itself.
Heart Anatomy and Function
Cardiac Chambers and Septa
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The heart is a four-chambered muscular organ located in the thoracic cavity between the lungs, posterior to the sternum, and slightly left of the midline
The right and left atria are the upper chambers of the heart that receive blood from the venous system (right atrium) and the lungs (left atrium)
The right and left ventricles are the lower chambers of the heart that pump blood to the lungs (right ventricle) and the (left ventricle)
The is a thick muscular wall that separates the left and right ventricles, preventing the mixing of oxygenated and deoxygenated blood
The separates the left and right atria
Coronary Circulation and Great Vessels
The coronary arteries, arising from the base of the , supply oxygenated blood to the myocardium (heart muscle)
The great vessels include:
: returns deoxygenated blood from the upper body to the right atrium
: returns deoxygenated blood from the lower body to the right atrium
: carry deoxygenated blood from the right ventricle to the lungs
: carry oxygenated blood from the lungs to the left atrium
Aorta: carries oxygenated blood from the left ventricle to the systemic circulation
Layers of the Heart Wall
Epicardium and Pericardium
The epicardium is the outermost layer of the heart, consisting of a serous membrane that reduces friction during heart contractions and provides protection
The pericardium is a fibrous sac that surrounds and protects the heart, anchoring it to the surrounding structures and preventing overfilling of the heart
Parietal pericardium: outer layer of the pericardium, attached to the great vessels and diaphragm
Visceral pericardium (epicardium): inner layer of the pericardium, directly attached to the heart surface
Myocardium and Endocardium
The myocardium is the middle layer of the heart, composed of cardiac muscle tissue responsible for the heart's contractile function
Cardiac muscle cells (cardiomyocytes) are striated, branched, and interconnected by intercalated discs
Intercalated discs contain gap junctions that allow for rapid electrical impulse propagation and coordinated contraction
The endocardium is the innermost layer of the heart, lining the chambers and valves, providing a smooth surface for blood flow and preventing blood clotting
Endothelial cells of the endocardium secrete nitric oxide (NO) and endothelin to regulate vascular tone and cardiac function
Purkinje fibers, specialized conduction cells, are found in the subendocardial layer and rapidly conduct electrical impulses
Function of Heart Valves
Atrioventricular (AV) Valves
The atrioventricular (AV) valves, namely the tricuspid (right) and mitral (left) valves, are located between the atria and ventricles
AV valves prevent backflow from the ventricles to the atria during ventricular contraction (systole)
The has three cusps, while the has two cusps (bicuspid valve)
The and anchor the AV valves to the ventricular walls, preventing the valves from inverting during ventricular contraction
Semilunar Valves
The , namely the pulmonary (right) and aortic (left) valves, are located at the base of the pulmonary artery and aorta, respectively
Semilunar valves prevent backflow from these vessels into the ventricles during ventricular relaxation (diastole)
Each semilunar valve has three crescent-shaped cusps that open and close passively in response to pressure changes
The cusps of the semilunar valves are thinner and more delicate compared to the AV valves, as they do not have chordae tendineae or papillary muscle attachments
Pulmonary vs Systemic Circulation
Pulmonary Circulation
The is the portion of the cardiovascular system that carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium
The pulmonary circulation is a low-pressure, low-resistance system compared to the systemic circulation
Pulmonary arteries have thinner walls and larger diameters relative to their systemic counterparts
Pulmonary capillaries have a larger total cross-sectional area, allowing for efficient gas exchange
The pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs, while the pulmonary veins carry oxygenated blood from the lungs to the left atrium
Systemic Circulation
The systemic circulation is the portion of the cardiovascular system that carries oxygenated blood from the left ventricle to the body tissues and returns deoxygenated blood to the right atrium
The aorta, the largest artery in the body, carries oxygenated blood from the left ventricle to the systemic circulation
Ascending aorta: initial portion of the aorta, gives rise to the coronary arteries
Aortic arch: curved portion of the aorta, gives rise to the brachiocephalic, left common carotid, and left subclavian arteries
Descending aorta: portion of the aorta that descends through the thorax (thoracic aorta) and abdomen (abdominal aorta)
The superior and inferior vena cava are the major veins that return deoxygenated blood from the systemic circulation to the right atrium
Superior vena cava: formed by the union of the left and right brachiocephalic veins, draining the head, neck, and upper extremities
Inferior vena cava: formed by the union of the left and right common iliac veins, draining the lower extremities, pelvis, and abdomen