Physiology: Skin & Temp Regulation Flashcards
Normal body temperature: Varies with: _ _ _ _ Humans are: homeo...
Humans are homeothermic Core body temp is normally 37 ± 0.5°C Above 41°C proteins start to denature Below 30°C lose consciousness Varies with external temp activity circadian rhythm menstrual cycle Core temperature is maintained by balancing heat loss and heat gain
Thermal Balance
Heat production --> Convection +/- Conduction +/- Evaporation - Radiation +/-
Body Heat production
~ 80 kcal/hr at rest
~ 600 kcal/hr at a brisk walk
would raise temp by 10C per 10 min
Convection
= “fluid” conduction
hence wind chill &
water chill
Important in blood too
Conduction
= heat transfer direct
between touching
objects
Evaporation
= respiration + sweating
~600ml/day at rest
But 4l/hour at extremes
loses 600kcal/l
Radiation
~ 60% of heat loss
Can be source of heat gain
Detection of body temperature: cold/warm
“Cold” receptors and “warm” receptors
Cold Pain
Heat Pain
Cold Pain –> Cold Receptors
Warmth Receptors –> Heat Pain
Detection of body temperature: p/c
Peripheral thermoreceptors
located in the skin, especially in face, scrotum
Central thermoreceptors
located in spinal cord, abdominal organs, hypothalamus
Warm Receptor - detection
increases frequency of signals during warm phase
reduced in cold phase
Cold Receptor - detection
increases frequency of signals during cold phase
reduced in hot phase
Change in environmental temperature —>
- –> peripheral thermoreceptors
- -> Hypothalamic thermoregulatory centre
- resposes to changes in temp
Change in core body temperature —>
- –> central thermoreceptors
- -> Hypothalamic thermoregulatory centre
- resposes to changes in temp
Response to cold stress
Heat generated within the body is increased by:
General metabolism:
- oxidative phosphorylation and other chemical reactions are not 100% efficient
Voluntary muscular activity:
- “futile” muscular activity
Shivering thermogenesis
involuntary muscular activity
Nonshivering thermogenesis:
- in humans, only significant in infants, due to brown adipose tissue
Response to cold stress
Heat loss from the body is reduced by:
Vasomotor control:
- sympathetic arteriolar constriction reduces delivery of blood to the skin
Behavioural responses:
- reducing surface area, adding clothing, moving to warmer environment
Complications of Cold Stress
& Who is at risk?
Hypothermia
a fall in deep body temperature to below 35ºC
Those at risk
neonates
big SA:volume, not much fat, don’t shiver well, but do have BAT
elderly
do not detect temp change so well, less shivering capacity, more immobile
vagrants
cold store workers
North Sea workers
outdoor pursuits
Cold StressTreatment
Treatment
dry/insulate to prevent further heat loss
slow re-warming with bag/blankets
internal re-warming with hot drinks and/or warm air
fast re-warming by immersion in water, extracorporeal circulation
Vascular & Cellular response to Cold Stress condition:
Frost bite Vascular vasoconstriction increase in viscosity promotes thrombosis causes anoxia Cellular ice crystals form in extracellular space increases extracellular osmolality causes movement of water from intracellular space cell dehydration and death
Winter mortality &
Cold stress
Winter mortality
40% excess mortality in winter in UK
partly due to increases in heart attacks and strokes following periods of cold weather
increased vasoconstriction and increased blood viscosity contribute
Response to heat stress
Heat production is minimised by:
Decreased physical activity
Decreased food intake
Heat loss from the body is increased by:
Vasomotor control
arteriolar dilation increases delivery of blood to the skin
Sweating
sympathetic cholinergic fibres increase evaporative heat loss
Behavioural responses
increasing surface area, removing clothing, moving to shaded area
Complications of heat stress
1.
2.
Heat exhaustion (heat illness) Heat stroke (heat injury)
Heat exhaustion (heat illness)
body temperature raised in range 37.5-40ºC
results in vasodilation and drop in central blood volume
caused by a disturbance of the body’s fluid/salt balance due to excessive sweating
symptoms include headache, confusion, nausea, profuse sweating, clammy skin, weak pulse, hypotension, tachycardia, fainting & collapse
Heat stroke (heat injury)
body temperature raised above 40ºC
body’s temperature control mechanisms fail
symptoms include hot dry skin (sweating ceased) & circulatory collapse
Who is most at risk of heat stress?
Those most at risk
neonates & the elderly
people doing physical work in hot humid environments
workers wearing non-breathable protective clothing
Treatment of heat stress
Treatment move to cool environment remove clothing fan sponge with tepid water give fluids (oral, intravenous)
Fever
Part of the body’s mechanism for fighting infection
Caused by endogenous pyrogens (IL-1, IL-6)
Concept of ‘set point’ controlled by the hypothalamus
- endogenous pyrogens shift the set point
- caused by local production of prostaglandins by cyclo-oxygenase in the hypothalamus
- explains why aspirin & paracetamol reduce fever
Analogy of a thermostat that has been reset
Body temperature regulates around a higher than normal body temperature
Mild fever is beneficial
Severe fever is dangerous
