Thermoregulation

Thermoregulation

An animal’s regulation of body temperature helps maintain homeostasis

Throughout their lives, animals continually exchange heat, water, and dissolved solutes with their environment. Several mechanisms have evolved that allow animals to make such exchanges while maintaining homeostasis. The first homeostatic mechanism that we examine is thermoregulation, the process by which animals maintain an internal temperature within a tolerable range. Thermoregulation is critical to survival because most of life’s processes are sensitive to changes in body temperature. Each species of animal has an optimal temperature range. Thermoregulation helps keep body temperature within that range, enabling cells to function effectively even when the external temperature fluctuates. Internal metabolism and the external environment provide heat for thermoregulation. Most mammals and birds, a few other reptiles, some fishes, and many insect species are endotherms, meaning they are warmed mostly by heat generated by their own metabolism. In contrast, most amphibians, lizards, many fishes, and most invertebrates are ectotherms, meaning they gain most of their heat by absorbing it from external sources. Keep in mind, though, that endothermic and ectothermic modes of thermoregulation are not mutually exclusive. For example, a bird is mainly endothermic, but it may warm itself in the sun on a cold morning much as an ectothermic lizard does. In the following two modules, we examine some of the ways that animals regulate their body temperatures.

Heat is gained or lost in four ways

An animal can exchange heat with the environment by four physical processes. Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when an animal is physically touching an object in its environment. Heat is always transferred from an object of higher temperature to one of lower temperature. In Figure 25.2, heat conducted from the warm rock (red arrows) elevates the lizard’s body temperature. Convection is the transfer of heat by the movement of air or liquid past a surface. In the figure, a breeze removes heat from the lizard’s tail (orange arrows) by convection. Radiation is the emission of electromagnetic waves. Radiation can transfer heat between objects that are not in direct contact, as when an animal absorbs heat radiating from the sun (yellow arrows). The lizard also radiates some of its own heat into the external environment. Evaporation is the loss of heat from the surface of a liquid that is losing some of its molecules as a gas. A lizard loses heat as moisture evaporates from its nostrils (blue arrow).

 

Lets answer this question:

1.     A lizard warming itself on a hot rock is an example of an....., Why?

2.     If you are sweating on a hot day and turn a fan on yourself, what two mechanisms contribute to your cooling?