Thermoregulation Flashcards
uses of body temperature measurements?
aid diagnosis and tracking of infections, timing of ovulation, abnormal core temperature, as well as visualising blood flow (e.g. inflammation)
what region of the brain plays key role in thermoregulation?
the pre-optic area of the hypothalamus
what are the inputs integrated by the pre-optic area of the hypothalamus?
cool and warm sensitive neurons, thermal sensors from skin, state of other physiological systems, and learnt responses
how is heat lost from the body? (4)
radiation, conduction, convection, evaporation of water
how much of the total energy transferred in biological chemical reactions is released as heat?
around 75%
what is the purpose of thermoregulation?
controlling energy released by enzymatic reactions, distributing it around the body and transferring it to the environment, to enable normal physiological function
what do most studies of physiological heat production use?
indirect calorimetry involving measurement of oxygen consumption and CO2 production
equation relating temperature, heat energy, SHC, mass?
temperature= heat energy/SHC/mass
what is 1 calorie equal to in J?
around 4.2J
what is endothermy?
the process of internal heat generation
what are homeothermic endoderms?
animals that have a stable temperature due to internal heat production
what is a homeotherm?
animal with stable/controlled body temperature
what is a heterotherm?
animal with different body temperatures at different times
what is a poikilotherm?
animal which conforms to external temperatures
what is a warm-blooded animal?
animal with warmer blood than the surroundings
what is 0K?
the point at which atoms stop vibrating
what is thermal energy?
measure of the amount of energy in system by virtue of its temperature
what organs are important sites for BMR?
liver and brain
BMR relationship to adipose tissue?
adipose tissue isn’t very metabolically active, doesn’t really contribute to BMR
what is the contribution of skeletal muscle to BMR?
highly variable
which organ is particularly temperature sensitive?
the brain- changes of around 1°C produces measurable declines in function
thermal sensitivity of muscle?
generally performs better when warmer than core body temperature, force of skeletal muscle drops dramatically in cold, as does cardiac muscle
what temperature does the heart stop beating at and why?
stops beating below around 25°C due to failure of electrical activity
temperature sensitivity of testes?
sperm production requires cooler temperatures in humans- not same requirement in
e.g. elephants which have internal testes
temperature sensitivity of skin?
can tolerate very wide range but sensory function changes (is worse in cold)
general effect of cooling on body?
reduced MR in turn reducing oxygen and blood flow requirements
why can cooling be useful during birth?
hypometabolism combined with anapyrexia can reduce damage caused by neonatal asphyxia
what are ‘shells’ in reference to endotherms?
temperature gradients within endotherms which change with environmental temperature and exercise, caused by heat flux
most to least reliable methods of measuring core temperature?
oral, forehead, axillary, tympanic, oesophageal, rectal
temperature fluctuation that isn’t cause for concern in humans?
36-38°C
what can core temperature rise to during intense exercise without causing issues?
around 39.5°C
what core temperature is life threatening in absence of exercise?
> 40°C
survival rate at around 41.5°C?
around 50%
what core temperature does survival rate become very low at?
around 45°C
problems caused by excessively low core temperatures?
don’t provide molecules with enough energy, protein flexibility decreases, lipid viscosity increases, blood viscosity increases which increases circulatory load, capillary perfusion decreases, some enzymes slow more than others, whole organs can fail (heart), timings in CNS go wrong due to altered ion channel kinetics
problems associated with excessively high core temperature?
protein flexibility decreases (potential irreversible denature), lipid fluidity too high, enzymes accelerate, timings in CNS can go wrong dure to altered ion channel kinetics, high rates of food and water needed
what does the stable temperature provided by endothermy allow for?
complexity, specialisations, steady-state modulation of temperature to organs (e.g. cooler brain than core), hibernation, high speed and strength
downsides of endothermy?
expensive energy cost, limits behaviour
average human temperature?
36.8°C
how much can human core body temperature vary by during the day, when is it lowest?
about 1°C during day, lowest at night
what individuals tend to have lower core temperatures?
aerobically fitter individuals, older individuals
what is the most common cause of hyperthermia?
infection
effect of haemoconcentration?
increased risk of thrombosis, increased cardiac workload
risk to cold extremities?
chilblains (inflammatory process associated with capillary bed damage) and frostbite (potentially irreversible damaged due to water crystals and osmolarity changes)
difference between hibernation and denning?
hibernation involves prolonged fall in core temp to only a few °C, denning involves less major drop by about 10°C
what is the feedback loop of thermoregulation?
core temperature