General characteristics of the veins
Vienna - the blood vessels that carry blood from the capillaries toward the heart. All veins form the venous system. The color depends on the blood veins. Blood is typically depleted in oxygen it contains decomposition products and has a deep red color.
The structure of the veins
In structure veins are close enough to the arteries, however, with its own characteristics, such as low pressure and low velocity blood flow. These features give some features of the walls of veins. As compared with the veins arteries are large in diameter, a thin inner wall and an outer wall of well defined. Because of its structure in the venous system is about 70% of total blood volume.
Vienna, below the level of the heart, for example, the veins in the legs, are two systems of veins - superficial and deep. Vein below the heart, for example, wrists are on the inner surface of valve which opens downstream of the blood. When Vienna is filled with blood, the valve closes, making it impossible to reverse the outflow of blood. The most developed valve apparatus in veins with strong development, for example, the veins of the lower body.
Superficial veins are located just below the skin surface. Deep vein is located along the muscles and allow the outflow of 85% of the venous blood from the lower extremities. Deep veins that connect to surface, called communicating.
By merging with each other, they form a large vein venous trunks, which flow into the heart. Veins are interconnected in a large amount and form venous plexus.
Functions of veins
The main function of veins is to ensure the outflow of blood, saturated with carbon dioxide and waste products. Besides, in the circulatory system through the veins enter various hormones from endocrine glands and nutrients from the gastrointestinal tract. Vienna regulate general and local blood circulation.
The circulation of blood through the veins and arteries varies widely. As blood enters the artery pressure of the heart during its reduction (about 120 mm Hg. V.), The pressure in the veins is only 10 mm Hg. Art.
Also worth noting is that the movement of blood through the veins occurs against gravity, therefore venous blood experiences the effect of hydrostatic pressure. Sometimes, in violation of the valves gravity is so great that it prevents normal blood flow. This stagnant blood in the vessels and deforms them. Then veins and are called varicose veins. Varicose veins are swollen appearance that justified the name of the disease (from the Latin. Varix, rod.p. varicis - «swelling»). Treatments for varicose veins today is very broad, from the People's Councils to sleep in such a position that the feet were above the level of the heart before surgery and vein removal.
Other disease - vein thrombosis. Thrombosis in the veins of blood clots (thrombi). This is a very dangerous disease, because blood clots, looking up, can move through the circulatory system to the lung vessels. If a clot large enough, when released into the lungs can cause death.