Vasoconstrictors and vasodilators
Blood pressure in a healthy organism is maintained at a relatively constant level. Shifts in blood pressure when emotions, muscular work and other conditions quickly equalized thanks to neuro-humoral mechanisms of self-regulation. The main role belongs to the neural mechanisms regulating reflex the heart, breathing and the lumen of blood vessels.
Reflex regulation not only support relatively constant blood pressure, but also carries out rapid redistribution of blood between the authorities in accordance with the current needs of the body.
Efferent nerves regulate blood vessel tone circular smooth muscle of the muscle membrane. Increased muscle tone of blood vessels reduces their clearance and increases its tone weakening.
Vasoconstrictors
The sympathetic nerves constantly maintained muscle tone of blood vessels (after transection vessels dilate due to loss of tone), and their irritation causes an increase in muscle tone of blood vessels and thus narrows their lumen.
All vasoconstrictors (vasoconstrictor nerves) – sympathetic. They consist of long cell processes located at nodes of the sympathetic nervous system.
The main vasoconstrictor nerve – celiac, which contains numerous sympathetic fibers coming to the blood vessels of the abdomen. To the blood vessels of hands and legs sympathetic vasoconstrictor fibers tested in two ways: as a part of the sympathetic nerves and blood vessels of the outer shell. The main role in the regulation of vascular tone belongs to the sympathetic nerves.
Vasodilators
Vasodilators (vasodilator nerves) are available in many mixed nerve trunks, nerve fibers supplying the skin and extremities, such as the shoulder and sciatic nerve. They are in general nerve trunks with vasoconstrictors such as in the splanchnic nerve. With the simultaneous stimulation of mixed nerve trunks that contain both vasoconstrictors and vasodilators, vasoconstrictors action prevails. In the working muscle is reduced vascular tone.
Some vasodilators fibers belong to the parasympathetic nervous system, such as fibers tympani and pelvic nerves. A small part of the vasodilator fibers belong to the sympathetic nervous system, such as fiber, expanding coronary vessels of the heart, blood vessels of the brain and oral mucosa in cheeks and soft palate.
All other vasodilators fiber, t. E. Most of them come out of the spinal cord are not on the front and on the posterior roots (antidromic fibers) (NI Verzilov, 1896). Thus sosudorasshiriteli belong to the autonomic nervous system, but have a different course of the nerve fibers.
In some cases, the expansion of blood vessels can also occur without the involvement of the spinal cord excitation transfer to the receptor on the smooth muscles along the branches of a long process of afferent nerve cells, ie. E., By the axon reflex (for example, the expansion of the cutaneous vessels at applying mustard).
Sosudorasshiriteley function is the regulation of the local blood supply to increase blood flow to the working body. According to Pavlov, sosudorasshiriteli also perform trophic function.
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