Thermoregulation Flashcards
What is core body temperature?
Why do we thermoregulate?
•Core body temp is normally 37 ± 0.5°C
Humans are HOMEOTHERMIC so we have a tight window in which we need to keep our core temperature to function properly.
What does body temperature vary with?
External temperature
Activity
Circadian rhythm
Menstrual cycle
4 methods of heat loss and gain?
- Radiation (60% of heat lost via this method. Can also gain heat eg lying in sun all day)
- Evaporation (sweat and respiration)
- Conduction (heat gain or loss via direct contact eg sitting on cold bench will chill you)
- Convection
What detects body temperature?
Cold and warm receptors
Can be CENTRAL and PERIPHERAL
Where are the peripheral thermoreceptors and the central thermoreceptors?
Peripheral = SKIN especially face and scrotum
Central = Abdominal organs, spinal cord and hypothalamus
What source of temperature do the peripheral and central chemoreceptors detect?
Peripheral chemoreceptors: Change in environmental temperature
Central chemoreceptors: Change in core body temperature
What do the peripheral and central chemoreceptors feed into?
Hypothalamic thermoregulatory centre
In response to cold - how is heat generated by 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
Nonshivering thermogenesis
in humans, only significant in infants, due to brown adipose tissue
How do we reduce heat loss in response to cold stress?
Vasomotor control
sympathetic arteriolar constriction reduces delivery of blood to the skin
Behavioural responses
reducing surface area, adding clothing, moving to warmer environment
What is hypothermia defined as?
A fall in deep body temperature to below 35 degrees
Who is at risk of hypthermia?
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 - people living in the outdoors
cold store workers
outdoor pursuits
North Sea workers
What is the treatment for hypothermia?
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 – peripheral vasodilation – less blood in the heart – can cause heart attack
What happens if cold stress is not resolved?
Progresses to FROST BITE
Frost Bite involves both X and Y mechanisms…
X = VASCULAR
Y = CELLULAR
What is the vascular response to cold stress (frost bite)
vasoconstriction
increase in viscosity
promotes thrombosis
causes anoxia
What is the cellular response to cold stress (frost bite)
ice crystals form in extracellular space
increases extracellular osmolality
causes movement of water from intracellular space
cell dehydration and death
Cold Stress accounts for X% excess death rates in winter?
WHY?
40%
Increased VC and viscosity of blood due to cold weather leads to increased strokes and MIs
In response to heat stress, how is heat production minimised?
Decreased physical activity and decreased food intake
How is heat loss from the body maximised during reponse to heat stress?
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
What body temperature is associated with heat exhaustion?
Body temperature raised in a range (37.5 - 40) degrees celcius
What is the physiological response to heat exhaustion?
Vasodilation and resultant drop in blood volume
Body’s fluid / salt regulation is disturbed as a result of excessive sweating
What are the symptoms of heat exhaustion?
headache, confusion, nausea, profuse sweating, clammy skin, tachycardia, hypotension, weak pulse, fainting & collapse
What temperatures are assocaited with heat stroke?
Body temperature raised above 40 degrees
body’s temperature control mechanisms fail
What are the symptoms of heat stroke?
symptoms include hot dry skin (sweating ceased) & circulatory collapse
Who is at the most risk to heat stroke?
neonates & the elderly
people doing physical work in hot humid environments
workers wearing non-breathable protective clothing
What is the treatment for heat stroke?
move to cool environment
remove clothing
fan
sponge with tepid water
give fluids (oral, intravenous)
What causes fever?
Part of the body’s mechanism for fighting infection
Caused by endogenous pyrogens (IL-1, IL-6)
What controls the ‘set point’ for temperature control?
Hypothalamus
How does a fever raise body temperature?
Prostaglandins have effect on endogenous pyrogens which shift the set point…
Aspirin & paracetamol reduce fever because they inhibit prostaglandins.
Describe set point and core body temp with relation to
a) exercise
b) fever
a) In exercise your core body temp is higher than the set point and so you heat up and sweat
b) In fever your set point is above your core body temp so your body starts off cold and ends up very warm
Mild fever is beneficial but severe fever can be dangerous
