This unit bases on body temperature regulation.

Animals are divided into:-

  1. Poikilothermic (ectothermic); where temperature changes with that of the environment, and gain heat from outside (Poikilos-various ……………………eclo-out, thermal-heat).
  2. Homothermic (endothermic); have constant temperature and generates heat from within the body (endo-inside).

Advantages of endothermy:-

  1. Allow organisms to remain active at all times and in all seasons and exploit a wide range of environments in which endotherms could not survive as they maintain a constant body temperature.
  2. Maintain an optimum body temperature which allows enzymatically controlled reactions to proceed.
  3. Ability to maintain a high metabolic rate to produce enough energy that quickness movement of response to stimuli, increases survival chances of the organism.
  4. Can generate energy rapidly when situation demands; such as escape from predations and pursuit of prey.
  5. More consistent activity levels allow for greater brain development and thus higher learning abilities than ecotherms.

Disadvantages of endothermy

  1. Generation of heat from metabolism/respiration within the body needs the organism to take in a lot of food, hence spend more time searching for food which may not be easy to certain times eg water.
  2. endotherms constantly lose heat to the environment in areas with temperatures lower than their body temperature that may require beeter insulation which would not be necessary for an ectotherm.
  3. Requires efficient cooling mechanisms when environmental temperatures are above body temperature to prevent overheating which would not be required by an ectotherm.
  4. the body temperature of all endotherms are something of a compromise; balancing the advantage of a high temperature increasing metabolic rate and the disadvantage of increased heat loss due to a greater temperature gradient between the internal and external environments; and this is not easy.

Advantages of ectothermy

  1. Low food intake since they do not generate heat from within/metabolism (respiration) makes them more successful at surviving desert habitats, where food is scarce.
  2. No loss of heat when environment temperature. Falls below body temperature
  3. No mechanisms for preventing overheating in hot environments, hence no wastage of energy.

Disadvantages of ecotothermy

  1. Ecototherms have limited activity if environmental temperature is in extremes of heat of cold, hence exploit a normous range of environments.

Their metabolic rate is normally kept low which affects response to stimuli when external temperature is low

How heat is lose and gained by organisms.

Heat gained.

  1. Through metabolism of food
  2. Heat reflects from objectives
  • Conventional currents.
  1. Conduction eg from ground
  2. Radiation

Heat lost

  1. Evaporation eg sweating
  2. Conduction
  • Convection
  1. Radiation eg from body to air, water or ground.

Regulation of temperature in ecototherms

They majorly use behavioural methods e.g.

  1. Sub bathing/basking
  2. Lying on warm surface e.g. rocks by lizards to gain heat in cold or raising body of warm surface to reduce overheating in hot.
  • Burrowing into crevices e.g. by lizards, snakes.
  1. Salivation over the neck and legs eg in tortoises to increase loss of heat by evaporation.
  2. Moving into share and wall cracks when body temperature becomes very hot.
  3. Thermal gaping in large reptiles eg crocodiles to allow loss of heat as water evaporates from their lungs and mouth.

Re-orientation of body with respect to solar radiation can vary surface area exposed to heating eg prostate posture of iguna alignes body at right angle to sun’s rays, helps raise its temperature in cold. Elevated posture reduced exposed surface and mouth and lower body temperature in hot.

  1. Some hibernate when or feed and their metabolism drops nearly to zero. Prior to this, accumulate a large store of brown fat which is oxidized during respiration provides much energy and metabolic water to sustain the hibernation is also an adaptation to low supply of food in water.
  2. Some activate. A type of dormancy in animals that occurs in very hot and dry periods of the year.

Diapouse occurs in insects. Diapause is a form of dormancy that occurs at any stage in the live cycle of an insect (ie egg, larva, pupa, adult, rymph). It is related to photoperiod and is a seasonal adaptation that through changes in brain secretion enables the species to survive hazardous environmental conditions and produce offspring in favourable conditions.

Physiological means

Very few show a slight degree of thermoregulation through activity of pigment cells which occur in their skins. In some reptiles a high temperature (40 0C) leads to bleaching of the colour to decrease heat absorption. A low temperature (50C) causes darkening and hence increased heat absorption

The colour changes are brought about by chromotophores in the stein.

Regulation of temperature in endotherms

Physiological, anatomical and behavioural adaptations/means are used.

Response to cold by an endotherm:-

Physical means

  1. Hair is raised by contraction of erector pilli muscles, trapping air near skin which is warmed up and act as an insulator. Birds have a similar mechanism for erecting filoplumes and down feathers.
  2. Vasoconstriction occurs:- superficial blood vessels (arterioles) contract, narrow their lumen hence reducing amount of blood reaching the skin surface, reducing heat heat loss by evaporation.
  • Exposed structures eg ears have special shunt vessels interconnecting the anterioles and venules that take blood to and from the superficial capillaries of the skin. These shunt vessels dilate in cold condition so that blood does not flow to the skin surface but by passes it.
  1. There is reduction in total volume of circulating blood, achieved by some of as blood being taken up into reservoirs like the spleen and liver.


Use of counter current heat exchange systems.

Extremities of animals in cold regions are maintained at lower temperature, than the core body temperature; reducing the temperature gradient between them and the environment. Reduction of heat loss from these extremities is achieved by counter current heat exchanges which occur e.g. in limbs of certain binds and mammals like flippers of the whale, limbs of ducts, human foot and hands that are in contact with the cold environment.

  • Arteries are in close association with veins such systems, thus blood in veins returning from limbs passes along side blood in arteries.
  • Heat from warm blood entering the limbs in the artery in transferred to cold blood in vein returning from it; by conduction. This results into two important aspects:-
  1. The peripheral capillaries of the limb are kept at a lower or similar temperature to that of the environment, minimizing heat loss.
  2. Cold blood is prevented from entering the core of the body, thus keeping it warm.

Sweat glands become less active.

  1. b) Metabolic methods
  2. Increase in metabolic rate especially of the liver and muscles. Low

temperature induce in increased activity of adrenal, thyroid and

pituitary glands which produce hormones that help increase

metabolism and production of heat.

  1. Shivering/increase in muscular tone where skeletal muscles

undergo rhythmic involuntary contractions to generate heat.

  1. Contraction of smooth muscle in the skin resulting in formation of

“goose flesh” that resemble pimples.

  1. Decrease in body surface area (huddling) i.e. skin is not stretched out to reduce heat loss by evaporation.

Anatomical means.

Insulatory means:-

  1. Animals in very cold habitat hence thick layer of subcutaneous fat that insulates e.g. seal, whale have thick layer of falt called blubber.

Insulation is also achieved by an external covering of fun and feather which are denser and thicker for cold region dwellers than those in hot regions. Both function by trapping warm air net to the body


Animals in cold regions are larger than their counter parts in warm regions, hence smaller surface area to volume. Animals is cold regions have smaller extremities than thee one in warm regions. To reduce surface area for heat loss.





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