Veins

General characteristic of veins

Veins – blood vessels which transport blood from capillaries towards heart. All veins create venous system. Color of veins depends on blood. Blood is grown usually poor by oxygen, contains decomposition products and has dark red color.

Вены

Structure of veins

On the structure veins are rather close to arteries, however, to the features, for example, the low pressure and small speed of the movement of blood. These features give some features to walls of veins. In comparison with arteries of a vein have the big sizes in the diameter, a thin internal wall and a well-marked external wall. Because of the structure in venous system there are about 70% of all volume of blood.

Veins, for example, the veins located lower than the level of heart standing, have two systems of veins - superficial and deep. Veins lower than the level of heart, for example, of a vein hold valves which open on the course of a current of blood on an internal surface. When the vein is filled with blood, the valve is closed that makes impossible the return outflow of blood. The most developed valve device at veins with strong development, for example, veins of a lower body.

Superficial veins are located under the surface of skin at once. Deep veins are located on the course of muscles and about 85% of a venous blood of the lower extremities provide outflow. Deep veins which connect to superficial are called kommunikantny.

Merging with each other, veins form large venous trunks which fall into heart. Veins connect among themselves in a large number and form veniplexes.

Functions of veins

The main function of veins is ensuring outflow of the blood saturated with carbon dioxide and decomposition products. Besides, various hormones from hemadens and nutrients from digestive tract get to circulatory system on veins. Veins regulate the general and local circulation.

Process of blood circulation on veins and on arteries strongly differs. Blood gets into arteries under pressure of heart during its reduction (about 120 mm of mercury.), in veins pressure makes only 10 mm of mercury.

Also It should be noted that the movement of blood on veins happens against gravity, in this regard a venous blood is influenced by force of hydrostatic pressure. Sometimes, at disturbances of operation of valves gravity turns out so big that it interferes with a normal blood-groove. At the same time blood stagnates in vessels and deforms them. Then veins also carry the name of varicose veins. Varicose veins have the blown-up appearance that varix, род.п is justified by the name of a disease (Latin. varicis — "swelling"). Types of treatment of varicose veins are very extensive today, from national councils to sleep in such situation that feet were higher than the level of heart to surgical intervention and removal of a vein.

Other disease – a vein thrombosis. At fibrinferment in veins clots (blood clots) are formed. This very dangerous disease since blood clots, having come off, can move on circulatory system to lung vessels. If blood clot enough big sizes, at hit in lungs can cause death.

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