Body processes

Vasodilation – Function, Task & Diseases


Vasodilatation is a widening of the vessels by relaxing the vascular muscles . This smooth muscle is controlled by the two antagonists sympathetic and parasympathetic in the autonomic nervous system. Anaphylactic (allergic) shock is life-threatening vasodilation.

What is vasodilation?

The autonomic nervous system controls a large number of vital body processes. The heartbeat , digestion , metabolism or blood pressure cannot be influenced at will, but are all controlled by higher-level brain centers and hormones .

Nerve impulses quickly adapt organ functions to changing circumstances. In particular, the nerve pathways of the sympathetic and parasympathetic antagonists determine the activities of the autonomic nervous system. They lead from the central nervous system to the individual organs .

All involuntarily controlled nerve fibers are called visceromotor nerve fibers and are under either parasympathetic or sympathetic control. The vasculature contains both visceromotor fibers of sympathetic and parasympathetic control.

Vasodilation is the involuntary relaxation of vascular smooth muscle indirectly induced by the parasympathetic nervous system. The relaxation of the muscles expands the vessels and thus increases the blood flow. The opposite of this relaxation process is vasoconstriction , which is carried out by the sympathetic nervous system and causes the vascular muscles to tighten. The lumen of the vessels is narrowed and the blood flow is reduced.

function & task

Vasodilation and vasoconstriction are vital processes of the autonomic nervous system. They adapt the blood flow to changing circumstances and are therefore necessary to maintain the circulatory system. Too sudden blood flow could overload the heart . Too little blood flow could destroy tissues or internal organs due to insufficient oxygen supply . 

The adjustment of the blood flow to a given situation does not have to be decided consciously, but takes place automatically. This automatic function is particularly helpful for reacting as quickly as possible to changing situations. The active control of vascular smooth muscle lies primarily with the sympathetic nervous system. It causes the muscles to constantly contract. The parasympathetic nervous system is responsible for vasodilation. Since it appears as an opponent of the sympathetic nervous system, it has an inhibiting effect on the influence of the sympathetic nervous system. This inhibition can weaken or invalidate the sympathetic nervous system’s contraction command. The vascular muscles relax and the blood vessels enlarge their lumen. This increases blood flow.

Vasodilation can be induced both actively and passively. The relaxation of the vascular muscles should be mentioned as an active method. Passive vasodilation, on the other hand, occurs when blood volume increases. In active vasodilation, the interaction of nerves and muscles is referred to as vasomotor function.

In addition to the visceromotor fibers, vasodilation is also controlled by local mediators. Bradykinin, acetylcholine or endothelin appear as such mediators, which stimulate the endothelial receptors . As such, the B2, the M3, and the ET-B receptors are grouped together. These receptors respond to the stimulation by producing nitric oxide and prostacyclin. The parasympathetic nervous system perceives the increased concentration of nitric oxide as a request to inhibit the sympathetic nervous system. It influences the sympathetic nervous system and allows the vessels to relax.

The role of nitric oxide is evident in flow-mediated vasodilation induced by flow-induced shear forces. The prerequisite for flow-mediated vasodilation is the work of the endothelium . Activation of endothelial potassium channels effluxes potassium , causing hyperpolarization . Calcium rushes in and activates endothelial nitric oxide synthases.

Diseases & Ailments

One of the most common complaints associated with vasodilation and vasoconstriction is migraine headaches . Inadequate vasodilation of the cerebral vessels triggers this type of headache. Vasoactive substances or relaxation training such as autogenic training can cause vasodilation, which can relieve headaches. 

Damage to the endothelium can also be associated with vasodilatation disorders. For example, when the endothelium no longer senses shear forces, its potassium channels do not open and nitric oxide synthases are not activated in sufficient amounts. The flow-mediated vasodilation is therefore often determined clinically in order to draw conclusions about the activity of the endothelium.

Symptoms and complications caused by vasodilatation can also occur as part of allergic reactions. In the event of vasodilatation, histamine can be released. This substance not only widens the blood vessels, but also reddens the skin and, in extreme cases, can trigger anaphylactic shock. Anaphylactic shock can lead to circulatory collapse and organ failure . The immune system shows such a reaction to chemical substances, for example. The increasingly released mediators constrict the bronchi and cause gastrointestinal symptoms .

This systemic reaction of the whole organism is potentially life-threatening. It causes the blood pressure to drop sharply due to the widening of the vessels. Fluid leaks from the vessels into the surrounding tissue. The pulse drops and unconsciousness occurs. The initial symptoms are relatively unspecific and range from vomiting , visual disturbances and dry mouth to shortness of breath and circulatory problems .

Anaphylactic shock can ultimately lead to circulatory and respiratory arrest . This life-threatening situation can only be reversed by rapid resuscitation. Adrenaline and similar substances may relieve the acute symptoms. Glucocorticoids and antihistamines or H2-receptor antagonists can also improve the patient’s condition.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.