The geographical distribution of animals reflects the temperature gradients they can survive in The optimal temperature range can differ markedly in various species and the animals have developed various biochemical, physiological and behavioral adaptations to maintain their optimal temperature as the input or output of heat varies due to activity, or climatic changes e.g. winter and summer. We will look at how the small e.g. suricates & large e.g. gemsbok animals adapt to living in the desert and how the polar bear and seals adapt to living in the arctic circle. But we will first discuss the ins and outs of heat regulation by looking at an example that all parents have experienced i.e. the human baby and in particular the problems of temperature control in the preterm baby. This will illustrate the principles which will then be discussed in relationship to wild animals.
The input output washbasin model is ideal for understanding temperature regulation as everyday examples abound. For example the temperature of a room in winter is regulated by increasing the input of heat by opening the hot water radiators or using the fireplace. The amount of heat loss is decreased by closing the windows, insulating the walls, and sealing any leaks in the door and window spaces.
Similarly we control our own temperature by altering heat input & output. The use of camping to illustrate this, is appropriate on this blog. We increase exogenous heat input by radiation by sitting at a campfire. We can also alter the endogenous input when we are cold by increasing the own body’s production (endogenous input) by increasing our voluntary movement (clapping hands) or involuntary shivering. We can also alter our heat output. Heat loss is by four routes: radiation, conduction, convection, and evaporation. The loss from all four routes increases as the exposed surface area increases. Remember smaller “objects” have a relatively greater surface area per unit volume e.g. baby animal has a greater relative surface area than an adult animal.
So when camping we try to decrease heat loss by these routes. We decrease our surface area by flexing our limbs.Radiant loss is decreased by sleeping on a mattress with a silver foil lining. Conductive loss is decreased by an air cell/rubber mattress and thick clothes. Convective losses from the wind are decreased by sleeping indoors or wearing windproof clothing i.e.”windstopper”. Evaporative heat loss is decreased by getting out of wet clothes as soon as possible. It is now easy to work out the steps we take to cool down e.g. stretch out to increase surface area, sit in shade & decrease activity, less clothes, swim, use a fan.
In the next blog we will discuss the ins & outs of heat balance in preterm babies