Capillaries do not function independently. The capillary bed is an interwoven network of capillaries that supplies an organ. The more metabolically active the cells, the more capillaries required to supply nutrients and carry away waste products.

A capillary bed can consist of two types of vessels: true capillaries, which branch mainly from arterioles and provide exchange between cells and the circulation, and vascular shunts, short vessels that directly connect arterioles and venules at opposite ends of the bed, allowing for bypass.

The regulation of tissue perfusion occurs in microcirculation. There, arterioles control the flow of blood to the capillaries. Arterioles contract and relax, varying their diameter and vascular tone, as the vascular smooth muscle responds to diverse stimuli. Distension of the vessels due to increased blood pressure is a fundamental stimulus for muscle contraction in arteriolar walls. As a consequence, microcirculation blood flow remains constant despite changes in systemic blood pressure. This mechanism is present in all tissues and organs of the human body. In addition, the nervous system participates in the regulation of microcirculation. The sympathetic nervous system activates the smaller arterioles, including terminals. Noradrenaline and adrenaline have effects on alpha and beta adrenergic receptors. Other hormones (catecholamine, renin-angiotensin, vasopressin, and atrial natriuretic peptide) circulate in the bloodstream and can have an effect on the microcirculation causing vasodilation or vasoconstriction. Many hormones and neuropeptides are released together with classical neurotransmitters.

Arterioles respond to metabolic stimuli that are generated in the tissues. When tissue metabolism increases, catabolic products accumulate leading to vasodilation. The endothelium begins to control muscle tone and arteriolar blood flow tissue. Endothelial function in the circulation includes the activation and inactivation of circulating hormones and other plasma constituents. There are also synthesis and secretion of vasodilator and vasoconstrictor substances for modifying the width as necessary. Variations in the flow of blood that circulates by arterioles are capable of responses in endothelium.