Arterioly

Arterioles are small-diameter blood vessels that extend from arteries to capillaries. They are the narrowest arteries and constitute a major site of vascular resistance, playing a key role in regulating blood flow to tissues and arterial pressure.

Structure: Arterioles typically range from about 10 to 100 micrometers in diameter. Their walls are thinner than those of larger arteries and consist of three layers: the tunica intima with endothelium, a tunica media composed mainly of smooth muscle cells, and a relatively sparse tunica adventitia. The proportion of smooth muscle increases toward the capillary beds, giving arterioles substantial contractile capacity.

Function and regulation: They adjust diameter in response to neural input, circulating hormones, and local metabolic cues. Autoregulation and the myogenic response help maintain stable capillary perfusion across a range of blood pressures. Metarterioles and precapillary sphincters at the boundary with capillaries enable selective routing of blood into specific capillary networks, coordinating tissue perfusion with metabolic needs.

Physiology and clinical significance: By constricting or dilating, arterioles set systemic vascular resistance and influence mean arterial pressure. Chronic arteriolar changes, such as hyaline arteriolosclerosis in hypertension or diabetic arteriolosclerosis, can impair tissue perfusion and contribute to end-organ damage.

Name usage: In English, the term is arterioles; arterioly is seen in some languages or historical contexts. Arterioles are a key component of the microcirculation, mediating the transition from arterial to capillary flow.