Physiology: Thermoregulation


Temperature varies enormously over the face of the Earth - extremes. 

E.g. boiling hot springs of Yellowstone National Park and interior of Antarctica temperature can fall bellow -80'C.

Living cells tolerate only a narrow range of temperatures, most cell function is limited to between 0'C and 45'C. Physiological processes are temperature sensitive. Going faster at higher temperatures. 

There is always an optimum temperature for a reaction to occur at. At higher temperatures the enzymes become denatured and stop working. 

Temperature and life: water-> heat -> cooler

Temperature balance may be altered by physiology and behaviour. 

Balance: increase in metabolic rate, increases temperature, blood flow to skin, muscle activity, piloerection, behaviour, conduction, convection, radiation, evaporation.

Convecion in muscles is much faster than by conduction.

Heat transfer through fur or winter coat is thought of as conduction.

Conducion: transfer of heat through a material substance that is macroscopically motionless. 

Convection: trasnfer of heat through a material substance by macrocopic motion of the substance.

Evaporation: of water from skin and respiratory passages takes heat away from an animals' body. 

Latent heat of vaporisation: amount of heat required to vaporise water.

570-595cal per gram of H2O at physiological temperatures.

Heating gram of H2O from 0'C to 100'C requires 100cals.

Highly effective cooling mechanism. 

All mechanisms may occur at once: solar radiation, direct radiation, diffused radiation, radiation, evaporation, wind, convection, conduction and reflected radiation. 

Birds flying past cold trees during winter night: bird at 15'C, tree at -10'C, exchange of radiation, net effect loss of heat from bird to tree.

Radient temperatures of the sky. 

In a clear night, temperature well below air temperature at ground level. 

Animals lose heat to night sky. 

Small mammals burrow into snow. 

Radiation: objects emit electromagnetic radiation.

Objects constantly exchanging electromagnetic radiation with other objects without touching. 

Solar radiation: dark surfaces absorb more than light surfaces (sun heat). 

Animals can change their skin colour, to increase and decrease solar heating by darkening or lightening their bodies. 

Evening cool lizard standing by rock still warm from sun, exchange of radiation. 

Energy budget: for body temperature to remain constant.


Heat(in)=metabolism + solar radiation (R abs)

Heat(out)=radiation (R out) + convection + conduction + evaporation

If heat enters the body through convection and or conduction, the sign of those factors changes to negative. 

Most cell function is limited to between 0'C and 45'C. Sensitivity of a physiological process to temperature can be described as a quotient, Q10.

Q10= Rt/(Rt-10)

Not temperature sensitive Q10 = 1

Temperature sensitive Q10 > 1

Most biological Q10 values are between 2 and 3. E.g. reaction rates double or triple as temperature increases by 10'C.

Not all of the temperature reactions in an animal have the same Q10. 

Precursor enxyme A > intermediate > enzyme B > product

                 Q10 = 3                               Q10 = 2

Temperature change can disrupt physiological function.

Maintain homeostasis: organisms…


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