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Arterioles supply high-pressure blood directly into complex vascular structures termed capillary beds (Figure 3.8). These function as distribution vessels ensuring that all cells within a tissue or organ are adequately perfused with oxygenated blood. It is useful to visualise capillaries as completing the circuit of blood flow by forming bridges between the arteries and veins of the body. Pre-capillary sphincters are tiny rings of smooth muscle which act as valves to regulate the flow of blood into each capillary bed; these are under the control of the autonomic nervous system and a variety of locally acting chemical signals and hormones.

Figure 3.8 Capillary bed structure

Source: OpenStax (2013) Anatomy and Physiology. Rice University. Available at: https://openstax.org/books/anatomy-and-physiology/pages/1-introduction