Hemeothermy Flashcards
Homeothermy
o Thermoregulation and endothermy
o Regulate Tb by physiological means
o Beneficial to operate in any environment, costly metabolically
Thermoneutral zone (TNZ)
Range of Ta over which an animal’s metabolic rate is constant; basal metabolic rate is measured within TNA under resting and fasted conditions
Lower-critical temperature
o Ta below which animal’s metabolic rate increases with further decrease in Ta
o Thermal gradient for dry heat transfer keeps increasing
o Insulation already at max, thermal conductance can no longer be minimized
o Heat generation much increase
Upper-critical temperature
o Ta above which animal’s metabolic rate increases with further increases in Ta
o Thermal gradients for dry heat transfer reversed
o Challenge is to dump excess metabolic heat fast enough, and prevent heat gain from environment
o Evaporative cooling becomes critical
Basal metabolic rate
the amount of energy expressed in calories that a person needs to keep body functioning at rest
Dry heat transfer
Sum total of HCond, HConvec, and HRad in uniform thermal environment
Linear heat-transfer equation
M=C(Tb-Ta), Linear equation, x-intercept is Tb
Insulation
o Animal can vary value of C within the TNZ
o Insulation or I = 1/C
o The inverse of conductance, means dry heat transfer is less likely
Hyperthermia
Tb greatly higher than normal
Pilomotor response
Small smooth muscle bundles at base of individual hair or feature can make it stand up or lie flat. Insulation increases when up.
Bergmann’s rule
Animals from higher latitudes/colder environmental temps tend to have larger body masses
Vasomotor responses
Constrict arterioles supplying blood to superficial veins; less warm blood comes into proximity with skin surface
Postural responses
Curling into fetal potion, reduces surface area, thus minimizing available area for heat transfer
Shivering thermogenesis
o Skeletal muscle contraction converts chemical energy in ATP to mechanical energy in the form of myosin movement
o Randomly activate motor units
o No useful movement but a boat-load of heat is liberated
Non-shivering thermogenesis
o Electron transport chain. As electrons move down chain, H+ ions pumped into intermembrane space. H+ ion gradient then produces ATP as H+ ion flow back into mitochondrial matrix
Brown adipose tissue (BAT):
major site for non-shivering thermogenesis and UCP1
Uncoupling protein 1 (UCP1)
o There are positioned in the inner mitochondrial membrane and allow H+ ions to flow down concentration gradient without producing ATP but generating a lot of heat
Sweating:
Dilute fluid with some Na+ secreted by sweat glands onto skin surface, increases evaporative H2O loss by 50X
Panting
o Increase breaking rate, water evaporates from respiratory tract into inhaled air, then exhaled.
o Minimizes Na+ loss but can potentially cause respiratory alkalosis and requires higher increase in metabolic rate
Gular fluttering
o Rapidly vibrate floor of mouth, increase air flow across upper respiratory tract
o Minimizes risk of respiratory alkalosis
Rete mirabile
o Specialized circulation cools arterial blood before entering brain.
o By cooling the brain (thermoreceptors) suppress AND activity that would otherwise lead to evaporative cooling
Allen’s rule
Animals from high latitude/colder environmental temps tend to have smaller appendages
