Through vasodilatation and vasopositioning, the autonomic nervous system, that is, the sympathetic and parasympathetic nervous systems, controls many bodily functions such as blood pressure, cardiac output, and thermoregulation. Basically, vasodilatation, which is achieved by relaxation of smooth muscle in the walls of blood vessels, causes an increase in blood volume in the vessels and a decrease in blood pressure.
What is vasodilatation?
Vascular dilatation, also known as vasodilation, is an increase in the volume of blood vessels that is achieved by relaxation of the smooth muscle tissue in the walls of the veins. Vascular widening, also called vasodilation, is understood as an increase in the volume of blood vessels achieved by relaxation of the smooth muscle tissue in the walls of the veins. The system of tension and relaxation is vegetatively controlled by sympathetic and parasympathetic nervous systems. As a rule, the stress hormones produced by the sympathetic nervous system lead to vasoconstriction and an increase in blood pressure. The parasympathetic nervous system, as an antagonist of the sympathetic nervous system, partially reduces the stress hormones and synthesizes hormones and neurotransmitters, which in principle lead to vascular widening. The vasodilatation does not occur in all the body’s vascular systems at the same time, but in the case of psychological stress the sympathetic nervous system ensures that the vessels supplying skeletal muscles are dilated and the peripheral vessels and those of the kidneys are constricted. Vascular dilation also plays a major role in thermoregulation to prevent excessive body temperature. The most important physiological mechanism here is a reduced calcium influx into the smooth muscle cells of the vessel walls. This causes the muscle cells to relax, resulting in an increase in volume, a vasodilatation. In special cases, such as severe blood loss, the body uses vasodilatation with simultaneous vasoconstriction of the peripheral vessels as an emergency program to supply the major organs with the remaining blood.
Function and task
The autonomically controlled vasodilatation and its counterpart, vasoconstriction, serve primarily to stabilize the circulation in the face of varying and changing demands. Via vasodilation, the autonomic nervous system controls circulatory functions such as blood pressure and cardiac output. It is of great importance that vasodilatation does not occur in an undifferentiated manner throughout the entire vascular system, but that sympathetic stress hormones such as adrenaline and noradrenaline cause vasodilatation in the muscles and some organs, but at the same time cause constriction of the peripheral vessels. In the short term, this allows the muscles to achieve maximum performance because they are better supplied with blood as a result of the vasodilatation. The simultaneous vasodilatation of the peripheral blood vessels ensures a lower risk of bleeding in the event of injury, and the temporarily reduced blood supply to the renal vessels results in reduced urine production. In stressful situations, vasodilation is part of the responses that optimally prepare the body for escape or attack. Physiologically similar, the body responds to traumatic conditions such as severe injury and high blood loss by releasing stress hormones. Remaining blood is concentrated in the body by vasodilatation, and constriction of peripheral vessels reduces further blood loss in the event of external injury. Vascular widening also plays a major role in thermoregulation. When the body’s thermoreceptors report that the body temperature has risen above the set point of about 37 degrees Celsius, the parasympathetic nervous system causes vasodilation of the peripheral blood vessels. This causes more blood to circulate in the peripheral vessels, so that the cooling effect is intensified by the passing outside air. The vasodilatation is then visible externally, especially in the face, by an emerging redness. The increased cooling effect also works in combination with perspiration to utilize evaporative cooling in high outdoor temperatures and/or during vigorous exercise that releases excess heat in the muscles. To some extent, vasodilation can also serve to communicate in body language. In the case of mental excitement, especially anger and states of aggression, predominantly the face, neck and décolleté become red.Red skin color, due to short-term increase in blood pressure and vasodilatation, signals the current condition and generally advises caution.
Diseases and ailments
Vascular widening is of great importance in the control of many homeostatic physiological processes in open dynamic systems. Especially in the adaptation of circulatory parameters such as blood pressure, heart rate, and cardiac output to the respective demand. Functional restrictions of vascular expansion can trigger acute and chronic problems. The best-known disruptive factor that can impair the physiological mechanism is arteriosclerosis. Deposits (plaques) in the walls of arteries make them inelastic, and as the disease progresses, the cross-section narrows. Relaxation of the smooth muscle cells in the vessel walls, induced by parasympathetic neurotransmitters, is then no longer fully effective. The blood pressure can no longer adapt sufficiently to the requirements. This is particularly noticeable in diastolic blood pressure (relaxation phase), which should rise only minimally when the body is under light continuous stress. In the case of arteriosclerotic changes in the vessels, the diastolic value rises significantly during continuous stress. Vascular dilatation must always be seen in the context of vascular tone. The interplay between sympathetically controlled tension and parasympathetically controlled relaxation is of great importance. In case of a disturbance of the interplay, a so-called vegetative dystonia is often diagnosed. However, this term is not used by all physicians because the disease cannot be defined exactly and there is a suspicion of an embarrassment diagnosis. With regard to dilatation of the vessels, the disturbed interplay can lead to a constant increased sympathetic tone with an increased stress hormone level drowning out the parasympathetic relaxation stimuli, so that no vascular dilatation for general blood pressure reduction occurs. Chronic high blood pressure (hypertension) results, which, if untreated, leads to severe secondary problems.
