Skin and Temperature Regulation Flashcards
What is the core body temperature of humans?
What happens above and below this temperature?
37 +/- 0.5 degrees
Above 41 degrees proteins start to denature
Below 30 degrees lose consciousness
What does normal body temperature vary with?
External temperature
Activity
Circadian rhythm
Menstrual cycle
Explain thermal balance
Core temperature is maintained by balancing heat loss and heat gain
Basal metabolic rate makes up the basis of heat production.
Heat is lost or gained by Radiation, Convection and Conduction
Heat is lost by evaporation
Explain heat production
About 80 kcal/hr produced at rest
About 600 kcal/hr at a brisk walk would raise temp 1 degree per 10 mins
This needs to be compensated for or we would overheat
Explain radiation
60% of heat loss
Just lost to atmosphere
Can also be a source of heat gain
Explain evaporation
Evaporation = respiration + sweating
Lose about 600ml/day at rest
But 4L/hr at extremes (600kcal/l)
Explain conduction
Conduction = heat transfer direct between touching objects
Can gain or lose heat
Explain convection
Convection = “fluid” conduction hence wind chill and water chill
Important in blood too
How do warm receptors respond to a rise in temperature?
Start off at base level
Increase in temperature causes a rapid increase in APs which then ease off to a higher base level than originally.
When temperature decreases the APs will briefly stop before continuing again and returning to a normal frequency
How do cold receptors respond to a rise in temperature?
Start off at base level
Temperature rises and APs stop briefly before starting again (but still at a lower frequency than normal)
When temperature drops again the APs rise and then settle back to base level
How do we detect body temperature?
Peripheral thermoreceptors
-located in the skin, especially in the face, scrotum
Central thermoreceptors
-Loacted in spinal cord, abdominal organs, hypothalamus
Where do peripheral and central thermoreceptors feed information into?
Hypothalamic thermoregulatory center
Heat generated within the body in response to cold stress 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
How does brown adipose generate heat?
Mitochondria uncouple proton pump gradient from ATP generation so that metabolism just produces heat
How is heat loss from the body reduced during 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?
A fall in body temperature to below 35 degrees
Who is at risk of hypothermia?
Neonates Elderly Vagrants Cold stone workers Outdoor pursuits North Sea workers
How are neonates at risk of hypothermia?
Big surface area to volume ratio
-core temperature close to surface
Not much fat
Dont shiver well
-motor control isnt fully developed
Do have brown adipose tissue though
How are elderly at risk of hypothermia?
Do not detect temp change so well, less shivering capacity, more immobile
How do you treat cold stress/ hypothermia?
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
What are the two processes that cause frost bite?
Vascular
Cellular
How do vascular cold stress complications cause frost bite?
- Vasoconstriction
- Increase in viscosity
- Promotes thrombosis
- Causes anoxia
How do cellular cold stress complications cause frost bite?
- Ice crystals form in extracellular space
- Increases extracellular osmolarity
- Causes movement of water from intracellular space
- Cell dehydration and death
How big a problem is winter mortality?
- 40% excess mortality in winter in UK
- Due to increases in heart attacks and strokes following periods of cold weather
- Increased vasoconstriction and increased blood viscosity contribute
Heat loss within the body in response to heat stress is increased by…
Vasomotor control
-Arteriolar dilation incraeses 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 is heat exhaustion?
(Heat illness)
-Body temperature raised in range 37.5-40 degrees
- 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
What is heat stroke?
(Heat injury)
-Body temperature raised above 40 degree
- Body’s temperature control mechanisms fail
- Symptoms include hot dry skin (sweating ceased) and circulatory collapse
Who is most at risk from heat stress?
- Neonates and the elderly
- People doing physical work in hot humid environments
- Workers wearing non-breathable protective clothing
What is the treatment for heat stress?
- Move to cool environment
- Remove clothing
- Fan
- Sponge with tepid water
- Give fluids (oral, intravenous)
What is fever?
Part of the body’s mechanism for fighting infection
Caused by endogenous pyrogens (IL-1, IL-6)
What is your set point temperature
Concept of set point controlled by the hypothalamus.
When you exercise, sit in sun etc your core body temperature rises above your set point and you feel hot
How is your set point temperature changed?
Endogenous pyrogens shift the set point
Caused by local production of prostaglandins by cycle-oxygenase in the hypothalamus
Explains why aspirin and paracetamol reduce fever
How does set point relate to fever?
In exercise your core temperature rises above set point and you feel hot.
In fever your set point rises above your core temperature.
Your core temp increases to catch up but you still feel cold.
Therefore core temperature is raised but you feel cold so shiver and wrap in blankets etc
What are the pros and cons of fever?
Body temperature regulates around a higher than normal body temperature
Part of the body’s mechanism for fighting infection.
Mild fever is beneficial
Severe fever is dangerous
