Evaporation of water is an effective way to lose heat

When the environmental temperature rises above the upper critical temperature for an endotherm, overheating becomes a problem. For an exercising animal, overheating can become a problem at even low environmental temperatures. Heavily

(a) Otocyon megalotis

(a) Otocyon megalotis

Animals Hot And Cold Climates

41.16 Adaptations to Hot and Cold Climates (a) The bat-eared fox lives on the dry plains of central and southern Africa. Its large ears serve as heat exchangers, passing heat from the fox's blood to the surrounding air. (b) The thick fur of the arctic fox provides insulation in the frigid winter. Its ears and extremities are relatively smaller than those of the desert fox.

41.16 Adaptations to Hot and Cold Climates (a) The bat-eared fox lives on the dry plains of central and southern Africa. Its large ears serve as heat exchangers, passing heat from the fox's blood to the surrounding air. (b) The thick fur of the arctic fox provides insulation in the frigid winter. Its ears and extremities are relatively smaller than those of the desert fox.

insulated arctic species usually have an area on the body surface, such as the abdomen, that has only a thin layer of fur and can act as a window for heat loss. Large mammals, such as elephants, rhinoceroses, and water buffaloes, have little or no fur and seek places where they can wallow in water when the air temperature is too high. Having water in contact with the skin greatly increases heat loss because water has a much greater capacity for absorbing heat than air does.

Evaporation of water from body surfaces can also cool an animal. A gram of water absorbs about 580 calories of heat when it evaporates. Water is heavy, however, so animals do not carry an excess supply of it. Furthermore, hot environments tend to be arid places where water is a scarce resource.

Therefore, sweating or panting are usually cooling methods of last resort for animals adapted to hot environments.

Sweating and panting are active processes that require the expenditure of metabolic energy. That is why the metabolic rate increases when the upper critical temperature is exceeded (see Figure 41.14). A sweating or panting animal is producing heat in the process of dissipating heat, which can be a losing battle. Endotherms can survive in environments that are below their lower critical temperature much better than they can in environments above their upper critical temperature.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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