BLOOD CIRCULATION IN THE SKIN
The skin has an extensive blood supply; 8–10% of the total blood flow in the body can be found in the skin. The heat lost from the body is regulated by altering the volume of blood flowing through the skin.
The arteries supplying the skin form a network at the junction of the subcutaneous layer with the der-mis. This junction is known as the cutaneousplexus. Branches from these arteries supply the adi-pose tissue located in the subcutaneous layer. Other branches supply the accessory structures as they travel toward the epidermis. These branches form an-other network at the junction of the dermis and epi-dermis that follows the contours of the papilla. This junction is known as the papillary plexus. The cap- illaries at this junction join and rejoin to form venules and veins. In many regions, such as the fin-gers, palms, toes, and ear lobes, direct connections, known as arteriovenous anastomoses, link arteri-oles and venules. These links allow blood diversion, without it entering the superficial capillaries from which heat dissipates.
The blood vessels to the skin are well innervated by the autonomic nervous system. Blood flow can vary widely in response to changing temperatures, from as little as 1 mL to 150 mL/100 g of skin per minute. The plexuses in the skin, to some extent, serve as blood reservoirs. When blood is lost, these vessels constrict, propelling blood into the systemic circulation to maintain blood flow to the vital organs.
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