Discuss thermoregulation in mammals.

The temperature of animals range between -20C in fish and invertebrates living in arctic waters, to +500C in desert-living animals. Birds and mammals have the ability to regulate their body temperature and maintain it at a relatively constant level which is different to that of their immediate external environment. Temperature is important to animals because an increase leads to an increase in rate of physical and chemical (metabolic) reactions. As temperature increases further the enzymes involved in reactions will begin to denature, and this offsets the potential benefit of higher temperature in increasing the rate of reaction.

Poikilothermic means having a variable body temperature while homeothermic means having a relatively constant body temperature. More recently terms such as ectotherm and endotherm have been used. An ectotherm animal is dependent upon external sources for heat gain while an endotherm is dependent upon internal heat production. Birds and mammals are essentially endotherms.
There are four ways in which animals exchange heat with the surrounding: conduction, convection, radiation and evaporation. Conduction is heat transfer between two bodies that are in direct physical contact with each other. Heat flow is from a region of higher temperature to a region of lower temperature. Convection is transfer of heat by movement of fluid, which may be either a liquid or a gas. As the gas/liquid moves past the solid, heat is transferred from the solid to the gas/liquid. Radiation is the transfer of heat between two bodies that are not in direct contact with each other. As the surface temperature of a body increases, radiative heat loss from that surface also increases. Dark-colored skin and fur is able to absorb more solar radiation than equivalent light-colored structures. Evaporation is heat loss through vapor as temperature increases, the amount of heat energy required to covert water from liquid to gaseous state decreases. Evaporation is thus an important means of heat loss. For instance when humans get hot they sweat; when birds and dogs get hot they pant.

Mammals principally increase production of heat through increased metabolic heat production in skeletal muscles whereby heat is a byproduct of intracellular metabolism consequent to the contractile process. In some instances such muscular movement may be voluntary e.g. rubbing of hands) but generally , increased muscular activity is involuntary and is termed shivering. Metabolic heat production can also increase through the activities of thyroid hormones. These hormones are released under the control of anterior pituitary gland. Mammals may also increase body temperature through pilo-erection whereby body surface hairs erect and trap a layer of still hair next to the skin and thereby reduce convective heat loss, and reducing blood flow to peripheral organs by vasoconstriction

The control of body temperature is an example of homeostasis and is regulated almost entirely by nervous feedback mechanisms. Almost all these mechanisms operate through temperature-regulating centers in the hypothalamus. For these feedback mechanisms to operate there must be temperature detectors to determine when the body temperature becomes either too high or too low. The receptors that monitor temperature are called thermoreceptors. There are those which detect cold and also those which detect warmth conditions. Thermoreceptors are found both in the skin and in the deep body tissues like in the abdominal viscera and around the great veins of abdomen and thorax. The first group monitor peripheral changes in temperature of the mammal while the second group monitor changes in the core temperature.

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marto answered the question on April 16, 2019 at 07:07