arterioler

Arterioler, commonly called arterioles in English, are the small branches of arteries that lead to capillary networks. They typically range from about 10 to 100 micrometers in diameter and serve as the primary resistance vessels of the circulatory system. By adjusting their diameter, arterioles regulate blood flow into capillary beds and contribute significantly to systemic vascular resistance and mean arterial pressure.

Anatomy and location: Arterioles are composed of an endothelial lining surrounded by a tunica media of smooth muscle cells. The smooth muscle layer is relatively more prominent than in larger arteries, allowing precise control of vessel radius. In some tissues the arteriolar segment includes metarterioles, which connect directly to capillaries and may contain smooth muscle rings that modulate flow into the capillary bed. The adventitia is typically thin, and the endothelial surface may interact with pericytes and the extracellular matrix in microvascular regions.

Function and regulation: The primary role of arterioles is to regulate regional blood flow and arterial pressure through vasoconstriction and vasodilation. Autonomic (sympathetic) nerves can induce constriction, while local factors such as nitric oxide, carbon dioxide, pH, and tissue metabolites promote dilation or constriction as needed. The myogenic response helps vessels constrict in response to increased pressure to protect capillaries, contributing to autoregulation of blood flow.

Clinical relevance: Arteriolar tone and structure influence conditions such as hypertension, where arterioles may undergo remodeling and thickening of the smooth muscle layer, increasing resistance. In diabetes and other microvascular diseases, arteriolar dysfunction can contribute to impaired tissue perfusion. In organs like the kidneys and brain, precise arteriolar control is essential for maintaining filtration and nutrient supply, respectively.