Vasomotorik

Vasomotorik, or vasomotor function, refers to the regulation of vascular tone by the smooth muscle in blood vessels. This regulation determines peripheral resistance, blood flow distribution, and arterial blood pressure. Regulation is achieved mainly by the autonomic nervous system, with additional modulation from the endothelium, circulating vasoactive substances, and local metabolic factors.

The sympathetic nervous system provides the principal control of vasomotor tone. Sympathetic nerves release norepinephrine that acts on alpha-1 adrenoceptors in most vascular beds, causing vasoconstriction. In some tissues, epinephrine can promote vasodilation via beta-2 adrenoceptors. Parasympathetic input to systemic vessels is minimal, so vasomotor tone is predominantly adrenergic. The endothelium releases vasoactive mediators such as nitric oxide, endothelin, and prostacyclin, which respectively promote vasodilation and vasoconstriction, allowing fine-tuning of tone.

Regulation involves central and reflex mechanisms, including the baroreceptor reflex that adjusts sympathetic outflow to maintain arterial pressure, and the chemoreceptor reflexes that respond to changes in oxygen, carbon dioxide, and pH. Local factors such as tissue temperature, metabolites (e.g., adenosine), and shear stress can modify tone independently of central commands, a process important for matching blood flow to metabolic demand.

Clinical relevance includes disorders characterized by vasomotor dysfunction, such as orthostatic hypotension and vasovagal syncope, Raynaud phenomenon, and autonomic neuropathies. Abnormal vasomotor tone also participates in conditions like septic shock, where loss of vascular tone leads to distributive hypotension. Therapeutic approaches often aim to restore or modulate vascular tone through pharmacologic agents that influence adrenergic receptors or endothelial pathways.