Skin and temperature control Flashcards
what is a humans core body temperature?
Core body temperature is normally 37 ± 0.5°C
what happens in temperatures above 41C?
above 41°C proteins start to denature
what happens below 30°C?
lose consciousnes
what does normal body temperature slightly vary with?
external temperature
Activity
Circadian rhythm
Menstrual cycle
what is core temperature maintained by?
balancing heat loss and heat gain
what is convection?
“fluid” conduction
hence wind chill and
water chill
Important in blood too
what is conduction?
heat transfer direct
between touching objects
heat production of the body?
~ 80 kcal/h at rest
~ 600 kcal/h at a brisk walk
would raise temp by 1 0C per 10 min
what role does radiation have on thermal balance?
60% of heat loss
Can be source of heat gain
what role does evaporation have on thermal balance?
= respiration + sweating
~600 ml/day at rest
But 4 l/hour at extremes
loses 600 kcal/l
how is body temperature detected?
what are peripheral thermoreceptors?
Located in the skin, especially in face, scrotum
what are central thermoreceptors?
Located in spinal cord, abdominal organs, hypothalamus
what effect does increased temperature/amplitude have on warm and cold receptors?
describe the mechanism of detection of body temperature?
how is heat generation within the body increased?
General metabolism:
Oxidative phosphorylation and other chemical reactions are not 100% efficient
Voluntary muscular activity
“futile” muscular activity
Shivering thermogenesis
Involuntary muscular activity
Non-shivering thermogenesis
Only significant in infants due to brown adipose tissue
how is heat loss from the body reduced by?
Vasomotor control:
Sympathetic arteriolar constriction reduces delivery of blood to the skin
Behavioural responses
Adding clothing, moving to warmer environment, reducing surface area
what is hypothermia?
A fall in deep body temperature to below 35 ºC
who is at risk to cold stress?
Neonates (big SA:volume, not much fat, do not shiver well, but do have BAT)
Elderly (do not detect temp change so well, less shivering capacity, more immobile
Homeless people
Cold store workers
Outdoor pursuits
how is cold stress treated?
Dry/insulate to prevent further heat loss
Slow re-warming with bag/blankets
Internal re-warming with hot drinks and/or warm air
Rapid re-warming by immersion in water, extracorporeal circulation
what are vascular consequences of cold stress?
Vasoconstriction
Increase in viscosity
Promotes thrombosis
Causes anoxia
what are cellular causes of cold stress?
Ice crystals form in extracellular space
Increases extracellular osmolality
Causes movement of water from intracellular space
Cell dehydration and death
what is winter mortality?
40% excess mortality in winter in UK
Partly due to increases in MIs and strokes following periods of cold weather
Increased vasoconstriction and increased blood viscosity contribute
what is heat production minimized by?
Decreased physical activity
Decreased food intake
what is heat loss from the body increased by?
Vasomotor control
Arteriolar dilation increases delivery of blood to the skin
Sweating
Sympathetic cholinergic fibres increase evaporative heat loss
Behavioural responses
Removing clothing, moving to shaded area, increasing surface area
when does heat exhaustion occur?
Body temperature raised in range 37.5-40 ºC
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, tachycardia, hypotension, weak pulse, fainting and collapse
when does heat stroke occur?
Body temperature raised above 40 ºC
Body’s temperature control mechanisms fail
Symptoms include hot dry skin (sweating stops) and circulatory collapse
who is most at risk of heat stress?
Neonates and the elderly
People doing physical work in hot, humid environments
Workers wearing non-breathable protective clothing
how is heat stress treated?
Move to cool environment
Remove clothing
Fan
Sponge with tepid water
Give fluids (oral, intravenous)
what is a 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 and paracetamol reduce fever
