Thermoregulation maintains body temperature within a range conducive to metabolism.

The maintenance of body temperature within a range that enables cells to function efficiently involves heat transfer between the organism and the external environment. Heat exchange involves the physical processes of conduction, convection, evaporation and radiation.

Ectotherms derive body heat mainly from their surroundings and endotherms derive it mainly from metabolism.

Homeotherms generally have a relatively constant core body temperature, while heterotherms have a variable body temperature.

Comparative physiology reveals diverse mechanisms of Thermoregulation among animals.

Many large flying insects generate metabolic heat by muscle contractions, and many have countercurrent heat exchangers that retain it.

Although the body temperature of most fishes matches the environment, some large, active species maintain a higher current heat exchanger.

Reptiles and amphibians maintain internal temperatures within tolerable ranges mainly by various behavioral adaptations.

Birds may thermoregulate by panting, increasing evaporation from a vascularized pouch in the mouth, and by passing blood going to legs through a rete mirabile system.

Mammals and birds can adjust their rate of metabolic heat production by shivering and non-shivering thermogenesis.

The marine mammals maintain their high body temperatures in cold waters by a thick layer of insulating blubber and countercurrent heat exchange between arterial and venous blood.

Thermogenesis involves mainly shivering, enzymatic activity, brown fat, and high cellular metabolism.

Thermoregulatory areas of the hypothalamus serve as the body’s thermostat, receiving nerve signals from warm and cold receptors and responding by initiating either cooling or warming processes.

Torpor, including hibernation and aestivation, is a physiological state characterized by a decrease in metabolic, heart, and respiratory rates. This state enables the animal to temporarily withstand varying periods of unfavorable temperatures or the absence of food and water.

Some Invertebrates have contractile vacuoles, flame-cell systems, antenna! (green) glands, maxillary glands, coxal glands, nephridia, or Malpighian tubules for osmoregulation.

The osmoregulatory system of vertebrates governs the concentration of water and ions; the excretory system eliminates metabolic wastes, water, and ions from the body.



Freshwater animals tend to lose ions and take in water. To avoid hydration, freshwater fishes rarely drink much water, have impermeable body surfaces covered with mucus, excrete a dilute urine, and take up ions through their gills.

Marine animals tend to take in ions from the seawater and to lose water. To avoid dehydration, they frequently drink water, have relatively permeable body surfaces, excrete a small volume of concentrated urine, and secrete ions from their gills.

Amphibians can absorb water across the skin and urinary bladder wall. Desert and marine reptiles and birds have salt glands to remove and secrete excess salt.

In terrestrial animals, such as reptiles, birds and mammals, the kidneys are important osmoregulatory structures. The functional unit of the kidney is the nephron, composed of the glomerular capsule, proximal convoluted loop of the nephron, distal convoluted tubule, and collecting duct. The loop of the nephron and the collecting duct are in the kidney’s medulla; the other nephron parts lie in the kidney’s cortex. Urine passes from the pelvis of the kidney to the urinary bladder.

To make urine, kidneys produce a filtrate of the blood and reabsorb most of the water, glucose, and needed ions, while allowing wastes to pass from the body. Three physiological mechanisms are involved: filtration of the blood through the glomerulus, reabsorption of the useful substances, and secretion of toxic substances. In those animals with a loop of nephron, salt (Nace) and urea are concentrated in the extra cellular fluid around the loop, allowing water to move by osmosis out of the loop and into the peritubular capillaries.

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