Physiological Regulation: Cardiac Output and Blood Perfusion
Blood provides an extremely large and important convective surface within organisms. Typically, blood flow to the skin is higher during warming, and the heart tends to beat faster (Turner 1987). Animals, especially reptiles, can regulate heat loss to the environment by controlling blood flow (Smith, 1979; Turner and Tracy, 1983). Alligators, for example, thermoregulate by changing cardiac output and controlling blood perfusion to their appendages (Turner and Tracy, 1983). According to correlational studies, blood flow to the appendages increases during the warming process (Figure 1). The vasodilation of subcutaneous capillaries increases blood flow near the surface of alligators’ appendages, which subsequently increases heat transport (Smith, 1979). The evidence of increased cutaneous blood flow in alligators’ limbs during the warming process supports the observation that alligators generally heat faster than they cool (Smith, 1979; Turner and Tracy, 1983). Similarly, alligators may use their periphery to insulate themselves as they decrease subcutaneous blood flow when confronted with lower temperatures (Smith, 1976). Although larger reptiles are more efficient at thermoregulating by these mechanisms, the control of cardiac output and blood perfusion are essential adaptations that even small alligators use to maintain body temperature (Smith, 1979).
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