Metarteriolen

Metarterioles are short vessels in the microcirculation that link arterioles to capillary beds. They begin at the end of an arteriole and extend to the distal capillary plexus, where blood can enter the capillary network or, via a thoroughfare channel, pass directly toward postcapillary venules. This arrangement positions metarterioles as a regulatory bridge between arterial flow and capillary perfusion.

Structurally, the metarteriole wall contains a sparse, often discontinuous layer of smooth muscle. This arrangement allows partial, localized regulation of flow along the vessel. At the junction with the capillary plexus, precapillary sphincters may be present in some tissues, capable of constricting or dilating to control entry into the capillary bed. Distally, a thoroughfare channel can continue from the metarteriole into postcapillary venules, enabling a faster arteriovenous shunt when capillary flow is reduced.

Functionally, metarterioles contribute to the dynamic distribution of blood flow according to tissue needs. By modulating the patency of precapillary sphincters and the conductance of the metarteriole and thoroughfare channel, they regulate how much blood reaches the capillary network versus bypassing it. Local metabolic signals such as oxygen, carbon dioxide, pH, and adenosine, as well as autonomic inputs, influence the tone of the smooth muscle, adjusting perfusion in response to activity and stress.

In summary, metarterioles serve as a key regulatory site in microcirculation, coordinating arterial input with capillary exchange and providing a mechanism for rapid redistribution of blood flow within tissues.