Are Precapillary Sphincter Innervated?

Adrenergic (sympathetic) innervation of the precapillary sphincters in the microcirculatory bed of the rat mesentery was studied with Falck-Hillarp's method. It was shown that the precapillary sphincters are characterized by high density of the adrenergic innervation structures and specific architectonics.

How are precapillary sphincters regulated?

Chemical signals work at the level of the precapillary sphincters to trigger either constriction or relaxation. As you know, opening a precapillary sphincter allows blood to flow into that particular capillary, whereas constricting a precapillary sphincter temporarily shuts off blood flow to that region.

What causes the precapillary sphincters to relax?

The smooth muscle of the metarterioles and the precapillary sphincters contracts and relaxes regularly causing intermittent flow in the capillaries: this is known as vasomotion. A local drop in pO2 is the most important factor causing relaxation of the precapillary sphincters.