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Homeostasis: Temperature control
Endothermic? Ectothermic? Learn more about temperature control and use our selected essays to gain inspiartion for your own work.
Describing and explaining temperature control
It is usually better to avoid the terms ‘warm blooded’ and ‘cold blooded’ when referring to animals, and instead use the correct terms endothermic and ectothermic. If the environmental temperature is high, it is possible for the body temperature of ‘cold- blooded’ animal (ectotherm), to be much higher than that of a ‘warm blooded’ (endotherm) animal. Ectotherms cannot control their temperature physiologically but they do have some adaptations, such as enzymes with lower optimum temperatures, that suit them to the climate in which they live.
An ectotherm’s activity level may be low when the temperature is low but being an ectotherm does have at least one clear advantage. A very large proportion of the food energy used by an endotherm is used to generate heat within the body to maintain core temperature. An 80kg man would need about 250kg of food a year, compared to that of an 80kg alligator, which could survive on 8.5kg. Ectothermy is an ‘economical’ way of life so ectothermic animals can survive in habitats too lacking in food for many endotherms. For example, many desert animals are ectotherms such as scorpions, snakes and beetles. Small mammals and birds, such as shrews or hummingbirds, need to eat almost constantly because their large surface area/volume ratio means they lose large amounts of heat to the surroundings. Large reptiles and snakes can go months without food, so are less affected by changes in the food supply.
Explaining temperature control
It helps to explain how temperature is controlled using the stages of stimulus, receptor, control mechanism and effector. This can also be helpfully used to define the terms negative feedback and homeostasis. It is important to remember that it is receptors in the skin that monitor external temperature and receptors in the hypothalamus that monitor changes in core temperature. If core temperature rises then vasodilation occurs. The lumen of the arteriole gets wider during vasodilation. Students often write, ‘the capillary moves closer to the surface of the skin so more heat is lost’. This is incorrect. Blood vessels cannot move up and down inside the skin. The arterioles of the capillary beds dilate, allowing more blood to flow in the capillaries that lie nearer to the skin surface. Some blood does flow in these capillaries all the time but the flow is increased when core temperature rises. It is also worth noting that capillaries do not contain smooth muscle so are incapable of constricting or dilating. Only arterioles in the skin can dilate. The method of heat loss should also be mentioned, i.e. convection, conduction and radiation.