Final answer:
The precapillary sphincters are bands of smooth muscle that control blood flow into the capillaries, responding to nerve and hormone signals to regulate blood supply according to the body's needs.
Step-by-step explanation:
The band of smooth muscle that adjusts blood flow into each capillary is known as the precapillary sphincter. These precapillary sphincters are circular rings of smooth muscle located at the origin of capillaries from the metarteriole.
They function to regulate the passage of blood, responding to various signals including nerve impulses and hormonal changes to either allow blood to flow into the capillaries for nutrient and waste exchange or redirect it via a thoroughfare channel directly into venules, bypassing the capillary bed.
Blood flow through the capillary beds is carefully managed according to the body's requirements. For instance, during physical exercise, these sphincters will adjust to ensure increased blood flow to the skeletal muscles through vasodilation, whereas after a large meal, blood may be directed towards the digestive system instead.
Similarly, during resting states or when oxygen demand decreases, these sphincters might constrict to reduce blood flow to certain capillary beds.