Plan
► Blood circulation, its function. Functional characteristics of parts and regions of circulatory system.
► Physiological properties of cardiac muscle.
► Manifestations of cardiac activity and methods of their investigation.
► Concept of cardiac cycle.
Blood Circulation, its Function. Functional Characteristics of Parts and Regions of Circulatory System
Circulatory system is a closed system through which the blood flows throughout the body. Circulatory system of a human consists of 4-chambered heart and vessels forming two circuits: greater, or systemic, and lesser, or pulmonary. Due to continuous flow of the blood through vessels the circulatory system can perform the following functions:
► transport of nutrients and oxygen to tissues that provides their metabolism;
► transport of products of metabolism to organs that excrete them out of the body;
► transport of biologically active substances, soluble salts and metabolites involved in humoral regulatory mechanisms in the body;
► transport of different components of the immune system (specific antibodies, phagocytes, etc.) and participation, in this way, in the mechanisms of immunological protection;
► participation in thermoregulation;
► participation in the mechanisms of hemostasis;
► participation in control of water-electrolyte balance;
► participation in control of acid-base balance (blood circulating through the vessels contains three buffer systems: protein, carbonate, phosphate);
Diversity of functions of the circulatory system is determined by structural and functional relationships in the circulatory system.
The first principal description of the systemic circulation was attempted by English physician William Harvey in 1628 in his book "Anatomic Study of Movement of Heart and Blood in Animals". Later on, this scheme was completed with the pulmonary circulation, and ever since it has been used to study the laws of flow of the blood through vessels (Fig. 17.1).