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The human capacity for physiologic adaptation to cold is minimal. This deficiency may cause problems, because seasonal changes in the outdoor environment are quite prominent, even in the temperate zones of the world. In this context, skin is important in thermoregulation, and cutaneous blood flow and the resulting skin temperature may vary widely to help preserve the core body temperature.1–3 Physiologic, behavioral, and environmental factors modulate skin responses to cold exposure.
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Core body temperature is maintained within a narrow range by thermoregulatory mechanisms that rely largely on control of the cutaneous blood flow. Arteriovenous anastomoses are abundant in acral areas, and they regulate the volume of blood that passes through the skin. When the skin is cooled, there is usually an immediate acute reduction in the amount of blood that flows to the surface. These events alter skin temperature, heat loss, and color. Skin reactivity and the anatomic pattern of blood supply differ in the skin of newborns, adults, and older people. For instance, a reticulate appearance of cooled skin is a common finding in young infants (Fig. 94-1).
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The parallel arrangement of large arteries and veins in the limbs allows countercurrent exchange of heat. Vasoconstriction due to cold results in shunting of blood from the superficial to the deep venous system, and heat is transferred from arteries to veins. Thus, the blood going to the acral part of the limbs is precooled, and less heat is lost to the environment. With such thermoregulation, the body can maintain a constant core temperature of approximately 37°C (98.6°F) over a range of external temperatures between 15°C and 54°C (59°F and 129.2°F).
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Normally, the skin is to some extent adapted to a cooler environment than the 37°C (98.6°F) of internal organs. Given the presence of many cold-adapted enzymes, the skin may even function more effectively when slightly cooled. In the case of adipose tissue, mild long-term exposure ...