Prekapilláris

Prekapilláris refers to the segment of the microcirculation that lies between the arterioles and the capillary bed. This transitional zone is typically formed by metarterioles and terminal arterioles, and in some tissues may include precapillary sphincters, which are smooth muscle structures at the entrance to capillaries. The exact presence and functional significance of explicit precapillary sphincters vary among tissues and species, and in many beds the transition from arteriole to capillary is gradual rather than discrete.

Anatomy and function: Prekapillaries connect small arterioles with the capillary network and can regulate the entry of blood into capillaries. Through constriction or dilation, these vessels influence capillary recruitment, surface area available for exchange, and the distribution of blood flow to different tissue regions. They act as a regulatory checkpoint that helps prioritize perfusion according to local needs and systemic conditions.

Physiological regulation: Blood flow in the precapillary segment is governed by local metabolic signals (such as carbon dioxide, hydrogen ions, adenosine, and potassium), endothelium-derived factors (including nitric oxide and endothelin), and neural or hormonal influences. This regulation supports autoregulation of tissue perfusion and can adjust capillary perfusion during activity or stress.

Clinical relevance: Altered precapillary control can contribute to inadequate tissue oxygenation in diseases such as diabetes, sepsis, or shock. Conversely, excessive vasoconstriction at this level can impair capillary perfusion. The concept is particularly studied in skeletal muscle, skin, and gastrointestinal mucosa, though its exact role varies across organs.

See also: capillary, arteriole, metarteriole, microcirculation.