Redistribution of blood in the body
The blood in humans and higher animals, distributed among authorities, depending on their activity. Working hard body supplied with blood, the blood supply is reduced to idle. In humans, at 100 grams of tissue prepared blood alone average cm3 / min kidney – 430 heart – 66 Liver – 57, brain – 53. The local expansion of blood vessels, leading to increased blood supply operating body called working or functional hyperemia. Working congestion caused by a change in an operating metabolic organ accumulation of hydrogen ions, potassium, as well as histamine and other metabolic products. Increasing concentrations in blood, increase metabolism, it causes at source dilation of arterioles and capillaries, and the center of vasoconstrictor substances act vice versa, ie. E. Increase the tone and, therefore, increase blood pressure.
The number of functioning capillaries increases in working muscle compared with broken more than 10 times, and the amount of blood flowing through the vessels heavily working muscle is increased to 50 times. At rest flowed in skeletal muscles about 20% of the circulating blood, and when severe muscular work – to 90%. It is particularly reduced blood supply to the kidneys and other organs of the abdominal cavity, and the blood supply to the brain is not changed.
Dilation of blood vessels in skeletal muscle (small arteries, arterioles and capillaries in muscle activity cause sympathetic cholinergic fibers. They increase the number of capillaries disclosed by 5-10 times, which is accompanied by a sharp increase in blood flow through the working muscles. At the same time the excitation of the motor area of the cerebral cortex of the brain a sympathetic cholinergic neurons of the sympathetic, units received impulses from the hypothalamic region, which leads to dilation of blood vessels in skeletal muscles and is several times increases the blood circulation in the conditioned and unconditioned motor reflexes.
Possibly, the working hyperemia in skeletal muscle and caused by another mechanism. It is assumed that in the walls of blood vessels have special muscle cells possessing high automaticity, known as pacemakers regulating smooth muscle tone, individual arterioles. Contraction of skeletal muscles, due to receipt of pulses along the motor nerves simultaneously gives contact between the pacemaker and vascular smooth muscle cells, which results in vasodilatation. However, to increase blood supply to the working body is insufficient local expansion of blood vessels therein. When the body increases blood volume due to its exit from blood depot, increased blood pressure and decreased blood vessel lumen of non-performing authorities. This is the result of reflex excitation vasoconstrictor center, caused by irritation of receptors in the working muscle metabolic products, as well as the stimulating effect of these substances and hormones (adrenaline and others.) On the center of the blood.
Thus, in other areas of the body vessels narrowed to a common blood pressure increases, and at the same time in a running body vessels dilated, and that it causes increased blood supply.
The same mechanism works in strengthening the blood supply to the abdominal organs during digestion.
The redistribution of blood is particularly great role capillaries that are subordinate to local influences than arterioles, and can change their clearance, regardless of the arterioles, often the opposite.
Redness or paleness of the skin of a person depends on the expansion or contraction of the capillaries and small veins (venules), t. E. The number of sketches contained in them, and the temperature of the skin – only on the rate of flow of blood through the arterioles, t. E. The intensity of the blood supply.
When expanding capillaries and arterioles the skin becomes red and hot. On the contrary, the narrowing of the capillaries and arterioles, pale and cold. If capillaries are expanded and narrowed arterioles and arterioles dilated, which is accompanied by an increase in the number of blood flowing through it, the skin is pale and hot.
By nervous system blood is redistributed in the major physiological states: during digestion, when physical work, mainly because of the emotions impulses passing through sosudosuzhivatelyam. Especially a lot of vasoconstrictor fibers available in the splanchnic nerves, they were supplied with numerous blood vessels of the abdominal cavity, skin and nerves, which sosudosuzhivateli sent to multiple vessels of the skin. Sosudosuzhivateley less suitable for the central nervous system, the heart and lungs.
During mental work blood supply of the brain increases while vasoconstriction other areas such as blood vessels of limbs, whose volume decreases. Increased blood supply skeletal muscle during operation is mainly due to narrowing of the vessels of the abdominal cavity and the portion of the skin and blood vessels, thus increasing the outflow of blood from the abdominal cavity and the skin. At rest in these vessels contains about half (45%) of the entire mass of blood. The action of splanchnic nerve as the most powerful vasoconstrictor nerve of the body, 3 / 4etoy blood squeezed into the general circulation and into the muscles and other organs working.
Upon excitation of the sympathetic nervous system and into the blood adrenaline (for muscular work, cooling, pain, emotion, and so on. P.) There is a reflex contraction of the spleen, which increases the amount of circulating blood.
During digestion amplified dilate blood vessels of the abdominal cavity while vasoconstriction skeletal muscle, and central nervous system, which increases blood flow to the abdominal cavity of 30-80%.
Numerous sosudosuzhivateli skin play an important role in regulating body temperature. Between vessels of the skin and blood vessels of the abdominal cavity often has an inverse relationship. When the narrowing of blood vessels of the skin, they are expanding and vice versa.
Pain causes vasoconstriction of the abdominal cavity and the skin and at the same time the blood flow to the skeletal muscles and the central nervous system due to the active and the passive part of the expansion vessels located therein.
For the blood supply is set to the length of the path of the blood of this body. Since all the vessels of a large range of difference in pressure in the aorta, and veins in the same hollow, blood flowing through the body, the faster the shorter the path of the blood. This is especially important for a large supply of blood to the heart, kidneys and brain. When the relative value of the blood supply to the rest of varies. The comparatively more than other organs are supplied with blood endocrine glands, kidneys, liver and brain.
While running, due to the expansion of the capillaries of muscles large amount of blood rushes to his feet. After the end of the run due to the cessation of the contraction of muscles, forcing blood to the heart, there is stagnation of blood in the legs. This can cause loss of consciousness as a result of outflow of blood from the brain – gravitational shock.
With the dramatic increase in the speed or deceleration time, but gymnastic exercises, or flying at high-speed aircraft and spacecraft blood is discarded in the direction opposite to the movement, which leads to faster and bigger the ebb and flow of blood to the brain, or from him.
The distribution of blood in the body and affects the position of the body and rest. When upright obstruction of blood flow up caused by the force of gravity balanced by the flow of blood from the top down. However, this lowered pressure on the walls of blood vessels located above the heart, and increases the pressure on the walls of blood vessels downstream of the heart, blood vessels of the lower limbs so further stretched. This counteracts the increase in the tone of stretching the artery walls of her and more developed muscular layer in the veins of the lower extremities. In the transition to the upright position in the vessels of the lower extremities ottekaet 300 – 800 cm3 of blood, its volume in the heart and the lungs decreases by approximately 20% and the systolic volume and cardiac output – by 25-40%. With this change of note particularly large changes in blood flow in adolescents (NL Fomin, 1974).
When you change the position of the human body from a horizontal and vertical (orthostatic test) blood supply to the brain is not disturbed due to a narrowing of the blood vessels of the abdominal cavity under the influence of splanchnic nerve.
Thus a large amount due to the outflow of blood from the abdominal vessels increases the total amount of circulating blood which reimburses outflow of blood to the feet, so the blood supply to the brain and heart not affected.
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