General and Sports Anatomy - L.V. Kapilevich, K.V. Davletyarova 2008

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Circulatory System

Vascular bed: Arteries, arterioles, capillaries (diameter 7-30 µm, total capillary diameter is 800 times greater than that of the aorta), venules, Veins, and anastomoses (Figure 28).

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Figure 28. The Circulatory system.

Arteries are Blood Vessels that carry blood away from The Heart, while veins carry blood toward the heart.

Veins feature pocket-like Valves that ensure blood flows in only one direction—toward the heart. Arteries lack valves.

Layers: the inner layer—tunica intima (endothelium); the middle tunic (elastic membrane, smooth Muscle); and the outer tunic (Connective Tissue, blood vessels, and nerves). Capillaries consist of a single layer of endothelial Cells resting on a basement membrane. They are the site of metabolic and gas exchange with Tissues.

Circulatory loops: the pulmonary (lesser) Circulation (right ventricle – Lungs – left atrium) and the systemic (greater) circulation (left ventricle – all body Organs and tissues – right atrium).

Peculiarities of the circulatory system Structure.

In the Kidneys, capillaries converge to form not a vein, but another artery—known as a portal system (rete mirabile).

The Liver receives blood via the portal vein, which branches into capillaries; blood then flows from these into the central VEINS OF THE lobules, which subsequently merge into the hepatic veins and empty into the INFERIOR VENA CAVA.

When blood flow is obstructed (e.g., due to trauma), collateral (alternative) circulation develops.

The heart.

2 ventricles (right and left) and 2 atria (right and left). The apex points downward, and the base is located at the top. Fibrous rings lie between the atria and ventricles, serving as attachment sites for The cardiac muscle.

The heart wall consists of three layers: the endocardium (endothelium), myocardium (cardiac muscle), and epicardium (serous membrane). Connective tissue forms the protective sac enclosing the heart (the Pericardium).

Valves: the right atrioventricular valve is tricuspid, and the left atrioventricular valve is bicuspid (mitral).

The aortic valve (semilunar, tricuspid) and the pulmonary valve (semilunar, bicuspid).

Heart contraction is referred to as systole, and relaxation as diastole (Figure 29).

Figure 29. The cardiac cycle.

Blood supply to the heart is provided by the right and left coronary arteries. Cardiac veins drain into the coronary sinus.

The heart is innervated by the vagus and sympathetic nerves. Specialized Regions of the myocardium within the heart ensure its automaticity—this is the cardiac conduction system. The primary (first-order) center of automaticity is the sinoatrial node, the secondary (second-order) center is the atrioventricular junction, and the tertiary (third-order) center is the ventricular conduction system (the bundle of His and Purkinje fibers).

Diagnostic Methods: ECG, echocardiography, ultrasound, tomography.