Arteriolar

Arteriolar refers to arterioles, the small-diameter arteries that connect muscular arteries to capillary networks. These vessels typically range from about 10 to 100 micrometers in diameter and form a key transition in the vascular tree between larger arteries and the microcirculation. The wall structure of arterioles is simpler than that of larger arteries, consisting mainly of endothelium and a tunica media rich in smooth muscle; the adventitia and external elastic lamina are relatively minimal. This muscular layer provides substantial control over vessel diameter.

The principal function of arterioles is to regulate blood flow and pressure within tissues. By constricting or dilating, they adjust vascular resistance, thereby controlling the amount of blood delivered to capillary beds and influencing systemic blood pressure. In many beds, pre-capillary sphincters or terminal arterioles coordinate with tissue metabolic demands to optimize perfusion. Autonomic nerves and local chemical mediators shape arteriolar tone.

Regulatory mechanisms involve sympathetic nervous system input and local factors such as nitric oxide, endothelin, prostacyclin, and other endothelial-derived signals. Myogenic responses to pressure changes also help sustain steady flow despite fluctuations in arterial pressure. Pathological remodeling of arterioles can disrupt perfusion, as seen in various cardiovascular and renal diseases.

Clinical relevance includes arteriolosclerosis, which manifests as hyaline changes in long-standing hypertension or diabetes, or hyperplastic changes in malignant hypertension. Arteriolar narrowing can contribute to organ ischemia, notably in the kidneys and retina. Treatments for hypertension often aim to reduce arteriolar resistance and restore appropriate tissue perfusion.