Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Cardiovascular System
General Provisions

The central organ of The Cardiovascular system is The Heart. It acts as a pump designed to circulate Blood through the vessels, capable of forcing blood into the Arteries and drawing it back from large Veins.

The Vascular System consists of the Circulatory system, in which blood circulates; The Lymphatic system, which contains Lymph; and the microvasculature. These systems are functionally interconnected.

The circulatory system performs a transport function in the body, which involves delivering nutrients, oxygen, and Hormones to Tissues, as well as removing Metabolic waste products and carbon dioxide from them.

The microvasculature comprises the hemomicrovasculature, through which blood flows, and the lymphomicrovasculature. The microvasculature serves to facilitate Metabolic exchange between tissues and blood (or lymph). The lymphatic system performs a drainage function, removing excess tissue fluid from the tissues.

Blood Vessels are subdivided into arteries and veins. Arteries are vessels through which blood flows away from the heart, whereas veins are vessels through which blood flows toward the heart. The Vessels of the hemomicrovasculature are located between the arteries and veins.

The walls of arteries and veins consist of three tunics: the internal, middle, and external. The internal tunic is formed by flat endothelial Cells. The middle tunic consists of Cytology/cytology/32.html">Smooth Muscle tissue and contains a certain amount of elastic fibers. The muscular layer is more prominent in arteries than in veins. The external tunic is built of Connective Tissue.

Arteries are distinguished into elastic and muscular types. The former contain a relatively high number of elastic fibers and have a yellowish hue (e.g., the aorta, carotid arteries). The latter include smaller arteries that are structurally closer to veins than to elastic arteries. Muscular-type arteries are capable of contracting, thereby regulating blood flow. Elastic-type arteries ensure the continuity of blood flow within the circulatory system, despite the pulsatile contractions of the heart.

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Fig. 12.1. Pathways of Blood Circulation (diagram):

1, 8 — hemomicrovasculature; 2 — aorta; 3 — left atrium; 4 — lung vessels; 5 — left Pulmonary veins; 6 — left ventricle; 7 — portal vein; 9 — INFERIOR VENA CAVA; 10 — Liver vessels; 11 — Thoracic duct; 12 — hepatic veins; 13 — right ventricle; 14 — right atrium; 15 — pulmonary trunk; 16 — SUPERIOR VENA CAVA; 17 — right pulmonary veins

Due to the high concentration of elastic fibers in their walls, arteries are denser and more elastic than veins. When cut, these vessels remain patent (open), whereas veins collapse on section. Unlike arteries, the internal tunic of many veins forms Valves. In shape, they resemble crescent-shaped pocket folds. Thanks to these valves, blood in the veins—particularly in the limbs—moves in only one direction, toward the heart.

From the heart, blood enters the SYSTEMIC AND PULMONARY circulations, and subsequently returns to the heart. The circulations were discovered by W. Harvey in 1628.

The systemic circulation refers to the part of the circulatory system that supplies blood to the entire body. It begins with the aorta in the left ventricle of The Heart and ends with the superior and inferior venae cavae in its right atrium. The Pulmonary Circulation refers to the part of the circulatory system that passes through the Lungs. It begins with the pulmonary trunk in the right ventricle of the heart and ends with the pulmonary veins in its left atrium (Fig. 12.1).

The Arteries of the systemic circulation carry so-called arterial blood, which is oxygen-rich and bright red. The VEINS OF THE systemic circulation carry dark red venous blood, which is oxygen-poor and carbon dioxide-rich. In the pulmonary circulation, the arteries carry venous blood, while the veins carry arterial blood.

Thus, blood vessels are named not According to the COMPOSITION OF THE blood they contain, but according to the direction in which it flows.

Each artery is accompanied by veins: large arteries by a single vein, and medium- to small-diameter arteries by two veins. Veins are typically divided into superficial (subcutaneous) veins and deep veins, which accompany the arteries.