Fig. 1.

Diagrammatic illustration of body temperature in the human body. a In cold environments, the area preserved at 37°C contracts and the shell area expands. b The body volume preserved at 37°C expands. Yellow areas in a, b, and c illustrate the "acral" regions that help control body temperature by constricting blood vessels when the body temperature falls. Arteriovenous anastomoses (AVA) found in the cutaneous vasculature of the acral regions open and close to allow or prevent, respectively, rapid heat loss from the skin. The concepts presented here are generalizations; a number of variables, such as gender, age, and individual difference can affect the temperature distribution (adapted from [10])