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NS 47 - Temperature Control (i) (humans are homeothermic (complex…
NS 47 - Temperature Control (i)
humans are homeothermic
constant ability to be active
unaffected by changes in environmental temp
can function in subzero conditions
complex regulatory systems (thermoregulation)
some animals lack thermoregulation (poikilothermic)
homeostasis
anticipatory controls, -ve feedback
thermal sensors
afferent + efferent pathways
integration system in CNS
target organs = muscles + sweat glands
energy expenditure to maintain homeothermic conditions
body temp maintained @ level optimal for metabolism
optimal enzyme activity
over 37.8: protein denaturation, cell damage
under 35.5: compromised metabolism, but less cell damage
37 degrees
over 39: heat stroke, brain lesions
under 30: cardiac fibrillation
metabolic food oxidation (80kcal/hr @ rest)
exercising muscle (friction-generated heat)
measuring temp
orally
rectally (0.56 degrees higher)
in ear
axillary (under armpit)
body consists of a core + shell
core
heat-generating
organs, CNS, muscles
37.8 degrees
constant, with some normal variation...
diurnal
1 degree difference (low in morning, highest from 5-7pm)
exercise (tremendous heat production, can increase by up to 2.3 degrees
menstrual cycle (higher by 0.5 degrees in 2nd half)
subject to precise regulation
increases due to more heat production + less loss
decreases due to less heat production + more loss
shell
insulating + exchanging according to environmental temp
skin (effector site) + subcut fat
cooler + temp varies a lot
e.g. skin can be 20-40 degrees
heat inputs + outputs
inputs = ext environment, int heat production
affect input-output balance
outputs = exposed body surfaces
heat transfer mechanisms
radiation
electromagnetic heat waves emitted/absorbed
gain from sun
loss to walls, furniture
humans lose 50% of heat through this
conduction
transfer between objects in direct contact
rate depends on
temp difference
thermal conductivity
good In H2O, poor in air
convection
transfer by currents of air/H2O (e.g. wind, blood)
can be enhanced by forced air movements (e.g. fanning)
cold air = denser than warm air
hence warm air rises from skin + is replaced by cold air (heat loss)
evaporation
heat lost through H2O turning to air on skin, resp airways, lining of mouth
insensible loss (CAN'T BE CONTROLLED)
heat transferred to/from blood vessels through radiation, conduction, convection