Precapilar

Precapilar is a term used in anatomy to denote structures located before capillaries in the microcirculation. In English, the corresponding term is precapillary. The precapillary segment includes small arteries known as precapillary arterioles that feed the capillary networks, and, in some texts, metarterioles that connect arterioles with venules. In many tissues, entry into the capillary bed is regulated by precapillary sphincters, smooth muscle rings at the entrance to individual capillaries. Their activity modulates the distribution of blood flow among the capillary beds of different tissues.

The precapillary region plays a central role in controlling tissue perfusion. By adjusting the diameter of precapillary arterioles and, in some cases, via sphincters, the circulation can direct blood flow to where it is most needed. This regulation supports both continuous capillary perfusion and the shunting of blood through thoroughfare channels when appropriate. The arrangement allows rapid responses to metabolic demand and changes in systemic or local conditions.

Regulatory mechanisms involve myogenic responses to intravascular pressure, metabolic signals such as low oxygen, high carbon dioxide, and adenosine, and endothelial factors including nitric oxide and endothelin. Neural and hormonal inputs can also influence precapillary tone. Disruption of precapillary function can affect tissue oxygen delivery and perfusion, contributing to microcirculatory dysfunction in various clinical contexts.

Etymology varies by language, with precapilar used in some linguistic contexts. The concept remains a part of the broader study of microcirculation and the regulation of blood flow at the level of the smallest resistance vessels.