Thermoregulation

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when temperature surrounding is very different. This process is known as homeostasis: a dynamic state of stability between an animal's internal environment and its external environment (the study of such processes in zoology has been called ecophysiology or physiological ecology).

Whereas an organism that thermoregulates is one that keeps its temperature constant and adapts to the temperature of the environment, thermoconformer changes its body temperature according to the temperature outside of it’s body.

Table of contents

1 Temperature regulation 1.1 Heat gains and losses in animals 2 Types of thermoregulation 3 Physiological temperature regulation in vertebrates 3.2 Ectotherms 3.3 Endotherms 3.3.1 Heat production in birds and mammals 4 Behavioral temperature regulation 4.4 Hibernation estivation and daily torpor

Temperature regulation

Life on earth exists within a narrow range of temperature which is stabilized by the unique properties of water within the bodies of organisms including animals; enzymes become denatured at temperature extremes and metabolic reactions occur best at certain temperatures; both endotherms, which control the build-up of heat from aerobic respiration (homeotherms) and ectotherms (poikilotherms) can thermoregulate but only the endotherms (birds and mammals) can maintain a stable body temperature by using their nervous, endocrine, respiratory and circulatory systems.

Heat gains and losses in animals

1. conduction - heat escapes from your body when you sit on a cold rock.
2. convection - cooler air currents remove heat from the surface of your skin.
3. evaporation - evaporative cooling occurs when water (often from perspiration) leaves the skin surface as a gas, lowering the body temperature by cooling blood vessels in the dermis.
4. radiation - e.g. acquisition of heat from solar radiation (e.g. snakes "sunning" on a cold day).

Types of thermoregulation

There are two types of thermoregulation that are used by animals:

1. physiological regulation: This is when an organism changes its physiology to regulate body temperature. For example, our body tends to sweat inorder to cool our body down. Another example is when our bodies get cold, it likes to shiver so that the body can create some heat.
2. behavorial regulation: This is when an organism changes its behavior to changes it body temperature. For example, when your body starts to get hot because of the sun, you may want to find a shade to cool yourself down.

Physiological temperature regulation in vertebrates

Ectotherms

Even though fishes are ectotherms some have developed the ability to remain functional even when the water temperature is below freezing and some even use natural antifreeze to resist ice crystal formation in their tissues; amphibians (also ectotherms) must cope with the loss of heat through their moist skins by evaporative cooling; reptiles, like amphibians must warm their bodies by behavioral adaptations; the stratum corneum they possess limits heat loss by evaporative cooling.

Endotherms

Main article: Endotherms

Birds avoid overheating by panting since, unlike the mammals, their thin skin has no sweat glands. Down feathers trap warm air acting as excellent insulators (sometimes used by humans). Hair in mammals also acts as a good insulator; mammalian skin is much thicker than that of birds and often has a continuous layer of insulating fat beneath the dermis - in marine mammals like whales this is referred to as blubber.

Heat production in birds and mammals

In cold environments, birds and mammals can compensate for heat loss by:

1. utilizing small smooth muscles (arrector pili in mammals) which are attached to feather or hair shafts; this shivering thermogenesis distorts the surface of the skin as the feather/hair shaft is made more erect (called goose flesh or pimples).
2. animals in cold climates tend to be larger (easier to maintain core body temperature) than similar species in warmer climates.
3. be capable of storing energy as fat for metabolism
4. have reduced extremities
5. some have countercurrent blood flow in extremities (e.g. timber wolves) to avoid freezing of tissues.

In warm environments, birds and mammals avoid overheating by:

1. behavioral adaptations like living in burrows during the day and being nocturnal
2. evaporative cooling by perspiration and panting
3. storing fat reserves in one place (e.g. camel's hump) to avoid its insulating effect
4. elongate, often vascularized extremities to conduct body heat to the air.

Behavioral temperature regulation

In addition to human beings, a number of animals also maintain their body temperature by physiological and behavioral adjustments. For example, a desert lizard alters their location continuously during a day. In the morning, some portion of its body, which is head, emerges from its burrow and later the entire body comes out of its hiding place and basks in the sun to aborb solar heat. As the sun gets stronger, a lizard hides under the rock or goer back to the burrows. Interestingly, as the sun goes down and the temperature is cooler, it emerges again.

By changing its behavior, a lizard can keep the body temporature to some degree. However, since a lizard is an ectoderm, she is not able to control the body temperature through metabolic regulation.

Some animals living in cold environment maintain their body temperature, preventing heat loss. They let their fur grow more to increase the insulation. Some arctic animals allow their body extremities to cool to very low temperature. Compared to the core body temperature, their legs or nose are extremely low nearly zero celsius, so they have nothing to lose heat in legs or nose. Because the extremities are not insulated well, high temperature in foot and hooves is hard to maintain.

Hibernation estivation and daily torpor

Rather than cope with limited food resources and low temperatures, some mammals "punt" in a sense by hibernating in underground burrows; in order to remain in "stasis" for long periods these animals must build up brown fat reserves and be capable of slowing all body functions; True hibernators (e.g. groundhogs) keep their body temperature down throughout their hibernation while the core temperature of false hibernators (e.g. bears) varies with them sometimes emerging from their dens for brief periods; bats are true hibernators which rely upon a rapid, nonshivering thermogenesis of their brown fat deposit to bring them out of hibernation.

Estivation occurs in summer (like siestas) and allows some mammals to survive periods of high temperature and little water (e.g. turtles burrow in pond mud).

Daily torpor occurs in small endotherms like bats and humming birds which temporarily reduce their high metabolic rates to conserve energy.