Blood and other body fluids, such as lymph and tissue fluid, make up the body’s internal environment. Blood is a special type of connective tissue, because phylogenetically and ontogenetically it is formed from the connective tissue of the germinal unit - mesenchyme. The circulatory system is a network of vessels and cavities of the heart through which there is a constant and continuous circulation of blood. What functions does the circulatory system perform? Answering this question, you can write a whole scientific treatise, because the functions of the circulatory system are diverse. This is the transportation of vital substances and biologically active compounds that provide nutrition and further development of all cells and tissues of the human body, this is the vital function of gas exchange, this is the maintenance of osmotic pressure by protein fractions circulating in the bloodstream. The function of the human circulatory system also includes the creation of an immune response that is adequate to the influence of external and internal factors, which could protect the body from infectious agents and other foreign elements alien to each specific individual.
The circulatory system could not have taken place if there had not been a constant, continuous throughout the life of the movement of blood, called blood circulation. A heart with countless blood vessels (large arteries, venous vessels, arterioles, capillaries and venules), as well as the lymphatic system make up the single vascular system of the human body. The functions of the circulatory system include the removal of oxidation products and other reactions that occur during the metabolism, which become very dangerous and toxic to cellular elements if they are not eliminated from the body in time. The structural elements of the blood create humoral regulation and provide complete control over the activity of all internal organs and each of the systems.
Blood, as a material substance of the circulatory system, consists of two parts: liquid, or plasma, as well as dry cocked shaped elements (platelets, red blood cells and white blood cells). The ratio of these fractions on average is 1: 1.5, and as a percentage of plasma it belongs to 40%, and 60% of all blood to the uniform elements. Plasma (liquid part) is a very complex and unique biological environment, 90% of which is water. The remaining 10% of all plasma is in proteins, amino acids, mineral complexes, glucose, buffer systems, hormones, dissolved gases, vitamins, enzymes, etc.
The functions of the circulatory system to ensure humoral immunity are associated with blood plasma. Regarding the shaped elements, it should be said that they have three completely different functions: for erythrocytes - respiratory, for leukocytes - protective, for platelets - coagulation.
Red blood cells contain an important iron-containing pigment called hemoglobin. Thanks to it, oxygen is transported from external air to the cells, and carbon dioxide is released from the cells into the external environment. There are several forms of white blood cells, and each of them has its own vitally important task. It is they who create cellular immunity, with their deficiency dangerous pathological conditions develop, a striking example of which is HIV infection. Clotting ability and aggregation property is inherent only to platelets, their lack causes pathological bleeding, both external and internal, and excess can cause blood clots that clog the lumen of blood vessels and block the normal flow of blood.
Whatever the function of the circulatory system, its role in human life is undeniable.