Lecture 8: Control of Body Temp Flashcards
Ectotherms: or
Poikilotherms: species that do not regulate their internal body temperature
–reptiles, amphibians and most fish
Endotherms: or
homotherms: species that regulate internal body temperature
- - examples; mammals and birds
homotherms have a relatively ___ core body temp
stable, about 37 degrees in humans
are there fluctuations in core temp?
YES
- -minimum in early morning, max in afternoon
- –also fluctuations linked to menstrual cycle (peak of ovulation about 0.5 degrees C increase)
key components of the system which controls core temperature
- thermal sensors
- Thermosensory afferent pathways
- integration system
- efferent pathway
- thermal effectors –> generate heat or dissipate heat
temp control =
negative feedback loop
when the body gets too hot:
- Brain notices increase
- blood vessels dilating
- sweating
- blood temp decreases
when the body gets too cold
- brain notices decrease
- 1.blood vessels constrict
- no sweating
- activation of brown fat
- blood temp increases
consequences of deviations in body temperature: 40-44 degrees c
-Heat stroke with multiple organ failure and brain lesions
consequences of deviations in body temperature: 38-40 degrees c
Hyperthermia ( as a result of fever or exercise)
consequences of deviations in body temperature: 36-38 degrees c
normal range
consequences of deviations in body temperature: 34-36degrees c
mild hypothermia
consequences of deviations in body temperature: 30-34 degrees c
impairment of temperature regulation
consequences of deviations in body temperature: 27-29 degrees C
cardiac fibrillation
normal cellular metabolism generates –>
heat
amount of heat generated by normal cellular metabolism depends on
the rate of energy consumption, by extension is linked to oxygen consumption
Respiratory Quotient: what is it
gives an indication of the type of fuel being utilised by the body
Respiratory Quotient: equation
CO2 eliminated / O2 consumed
–> varies depending on fuel source
resting metabolic rate is the =
energy consumption necessary for the basal functions of resting cells
the resting metabolic rate dissipates energy equivalent to ____ as heat
85 watt bulb
the active metabolic rate dissipates energy equivalent to ____ as heat; what happens when heat is not removed from the body??
1000 watt bulb
–core temperature would increase by 1C about every ten minutes (limiting duration of exercise)
heat balance basic equation
storage of heat = Heat production - Heat losses
heat production =
Metabolism - Work done on the environment
heat losses =
radiative heat loss + convective heat loss + evaporative heat loss
Transfer of heat around the body and away from the body:
heat is carried from active tissues to the body core, to prevent body overheating the heat must be transferred away from core to the skin
- main route = Convection
- minor route = conduction
heat loss from skin:
- evaporation
- radiation
- convection
convection stable/variable?
variable; depends on blood flow to skin
conduction stable/variable?
relatively constant; depends on conductive properties of subcutaneous fat
radiation heat transfer depends on :
Temperature gradient between the skin and object, surface area available and transfer co-efficient
Becomes noticeable at extremes – sunbathing – next to a fire, outside on a cold night.
conduction:
transfer of heat by touching an object of different temperature e.g. ice pack, lying on hot sand
convection:
when air or water carried heat between the body and the environment.
Influenced by: temperature gradient and also movement of air/water over the body
– wind = chill
2 types of evaporation:
sensible (sweating) and insensible (loss of water by breathing)
– linked to SA available and water pressure gradient between skin and environment
thermo-sensors:
sensors in the skin and temperature-sensitive neutrons in the hypothalamus
central sensors:
excellent for monitoring core temperature, but can’t track environment.
Peripheral- skin thermoreceptor 2 classes:
Warmth: linked to activation of TRPV1-4 –> 30-48 degrees C
Cold: linked to activation of TRPM8 –> 15-42 degrees C
Provide information about ambient temperature and blood perfusing the skin
TRPV1-4 & TRPM8 :
CATion channels, temperature sensitive
what shivers =
skeletal muscles
warmth-sensitive neurones have an ___ affect on heat genesis pathway
inhibitory effect
inhibit generation of heat
warmth sensitive neutrons detect
core temperature
skeletal muscle shiver and Brown adipose tissue (BAT) stimulation =
heat
stimulation of warmth sensitive neurons =
inhibition of pathway, leading to vasodilation and sweating! inhibits shiver and BAT command
what stimulated Warmth-sensitive neurons
warm and cold skin thermoreceptors
