prekapillär

Prekapillär, or precapillary, refers to the segment of the microcirculation that precedes capillaries, typically at the distal end of arterioles or at metarterioles. In this region, smooth muscle can form a sphincter-like structure intended to regulate blood flow into the capillary bed.

Anatomy and location vary among tissues. Precapillary control is often described at the junction between arterioles or metarterioles and capillaries. In some tissues, a discrete precapillary sphincter is proposed to exist, while in others regulation occurs more diffusely along the vascular wall or through the thro ughfare channel of the metarteriole.

Physiology and function are centered on perfusion regulation. The precapillary segment responds to local metabolic needs, oxygen tension, carbon dioxide, adenosine, pH, and shear stress, adjusting resistance to control the distribution of blood within the microcirculation. This can influence capillary recruitment, diffusion distance for oxygen and nutrients, and the transit time of red blood cells. Autoregulatory mechanisms and, to a lesser extent, autonomic input help coordinate flow with tissue demand.

Clinical relevance and variability are notable. The existence and functional importance of true precapillary sphincters are not uniform across all tissues, and some researchers emphasize that flow regulation occurs along the broader arteriolar-capillary continuum rather than at a discrete sphincter. Abnormal precapillary control can contribute to microcirculatory dysfunction in conditions such as hypertension, sepsis, and shock.

See also microcirculation, arterioles, metarterioles, capillaries.