THERMOREGULATION OBJECTIVES

CHAPTER VIII THERMOREGULATION OBJECTIVES

After completing this lesson, you will be able to:

5. Raise a question about thermoregulation;

6. Define thermoregulation;

7. Define endothermy and ectothermy;

8. Interpret data about thermoregulation;

9. Applying concept about thermoregulation

The outer ears of the jackrabbit (Lepus alieni) are thin and remarkably large. They provide this hare with an acute sense of hearing, a primary defense against predators. The ears also help the jackrabbit shed excess heat. Blood flowing through each ear's network of vessels transfers heat to the surrounding air. At times, however, blood flow in the ear could be a liability. When the air is hot, blood passing through the ears could absorb heat,

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raising body temperature to dangerous levels. So how does a big-eared jackrabbit survive in the midday desert heat? To answer this question, we need to look more closely at the biological form, or anatomy, of the animal. Over the course of its life, a jackrabbit faces the same fundamental challenges as any other animal. All animals must obtain oxygen and nutrients, fight off infection, and produce offspring. Given that they share these basic requirements, why do species vary so enormously in makeup, complexity, organization, and appearance? The answer is that natural selection favors, over many generations, the variations appearing in a population that best meet the animal's needs. The solutions to the challenges of survival vary among environments and species, but for the jackrabbit and other animals, they frequently result in a dose match of form to function. Because form and function are correlated, examining anatomy often provides clues to physiology-biological function. In the case ofthe jackrabbit, researchers noted that its large pink-tinged ears turn pale when the air temperature exceeds 4O'C (104°F), the normal temperature of the jackrabbit's body. The color change reflects a temporary narrowing of blood vessels in response to a hot environment. With their blood supply reduced, the ears can absorb heat without overheating the rest of the body. When the air cools, blood flow resumes, and the large ears again help release excess heat. Next, we will discuss how animals regulate their internal environment, using body temperature regulation to introduce and illustrate the concept of homeostasis (Campbell, 2012).

EXERCISE A Raising Question Based to the text, raise a question about the concept of ecology, and

the find out what the answer is! Question

Answer : .............................................................................................................

Thermoregulation definition

Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range. Thermoregulation is critical to survival because most biochemical and physiological processes are very sensitive to changes in body temperature. For every lO o

C decrease in temperature, the rates of most enzyme-mediated reactions decrease two- to three fold. Increases in temperatures speed up reactions but cause some proteins to become less active. For instance, the oxygen carrier molecule hemoglobin becomes less effective at binding oxygen as temperature increases. Membranes can also change properties, becoming increasingly fluid or rigid as temperatures rise or fall, respectively. Each animal species has an optimal temperature range. Thermoregulation helps keep body temperature within that optimal range, enabling cells to function effectively even as the external temperature fluctuates (Campbell, 2012).

Endothermy and Ectothermy

Internal metabolism and the external environment provide the sources of heat for thermoregulation. Birds and mammals are mainly

Animals that are mainly endothermic are known as endotherms; those that are mainly ectothermic are known as ectotherms. Keep in mind, though, that endothermy and ectothermy are not mutually exclusive modes of thermoregulation. 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. Endothermic animals can maintain stable body temperatures even in the face of large environmental temperature fluctuations. For example, few ectotherms are active in the below-freezing weather that prevails during winter over much of Earth's surface, but many endotherms function very well in these conditions. It is showed in figure below (Campbell, 2012).

A walrus. an endotherm

In a cold environment, an endotherm generates enough heat to keep its body substantially warmer than its surroundings. In a hot environment, endothermic vertebrates have mechanisms for cooling the body, enabling them to withstand heat loads that are intolerable for most ectotherms (Campbell, 2012).

Because their heat source is largely environmental, ectotherms generally need to consume much less food than endotherms of equivalent size-an advantage if food supplies are limited. Ectotherms also usually tolerate larger fluctuations in their internal temperatures. Although ectotherms do not generate enough heat for thermoregulation, many adjust body temperature by behavioral means, such as seeking out shade or basking in the sun (See figure below). Overall, ectothermy is an effective and successful strategy in most environments, as shown by the abundance and diversity of ectothermic animals (Campbell, 2012).

A lizard, an ectotherm

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Radiation is the emission of electrmagnetic waves by all object warmer than absolute zero. Radiation can transfer heat between object that are not in direct contact. Evaporation is the removal of heat from the surface of a liquid that is losing some ot its molecules of gas. Convection is the transfer of heat by the movement of air or liquid past a surface. Conduction is the direct transfer of thermal motion (heat) between molecules of object in direct contact with each other (Campbell, 2012).

Heat is always transferred from an object of higher temperature to one oflower temperature. The essence of thermoregulation is maintaining rates of heat gain that equal rates of heat loss. Animals do this through mechanisms that either reduce heat exchange overall or that favor heat exchange in a particular direction. In mammals, several of these mechanisms involve the integumentary system, the outer covering of the body, consisting of the skin, hair, and nails (claws or hooves in some species).

A key organ of this system is the skin, which consists ofthe epidermis and the dermis. The epidermis is the outermost layer of skin and is composed mostly ofdead epithelial cells that continually flake and fall off. New cells pushing up from lower layers replace the cells that are lost. The inner layer, the dermis, contains hair follicles, oil and sweat glands, muscles, nerves, and blood vessels. Beneath the skin lies the hypodermis, a layer of adipose tissue that includes fat-storing cells as well as blood vessels (Campbell, 2012).

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