Thermoregulation Flashcards
What is the normal range for the core temperature What is the core temperature When would it vary? What temperature would -death by heatstroke -hyperthermia -fever, exercise -hypothermia -LOC -death by VF occur
36.5-37.5
Temp around body of main organs
-stable in ambient temp of 20-30C
Death by heatstroke
-42+
Hyperthermia
-40+
Fever, exercise
-37.5+
Hypothermia
-36.5-
LOC
-30-
Death by VF
-27-
How would you measure the temperature of the body
What are the pros and cons of each method
Oral
- simple, NI
- underestimation by 0.5C
Aural
- fast
- uncomfortable, unestimate
Rectal
- close to CT, continuous
- slow
Oesophageal
- close to CT, continuous
- affected by oral intake
GI (temp pill)
-continuous, varies along GI tract
What generates heat? What proportion of energy is used by -BMR (awake+sleep) -Food thermic -NEAT -EAT
How is our core temperature maintained
Metabolism generates heat
- BMR => 60%
- Food thermic => 8%
- NEAT => 7%
- EAT => 25%
Skeletal muscle generates heat => lost to maintain CT
Describe these 4 methods of heat transfer
- radiation
- convection
- Conduction
- Evaporation
Radiation
-release of IR radiation down temp grad
Convection
- hot, less dense air rises
- cold, more dense air falls
- forced convection can increase heat loss (via the wind chill effect)
Conduction
- mv of hot => cold via an object
- reduced with insulators
Evaporation
- loss of water => heat loss
- increased BMR => increased sweating => maintain CT
Describe the feedback loop involved in thermoregulation
Receptors detect change in temperature
Hypothalamic control center
Sends efferents to effectors
Describe the function of the hypothalamus in thermoregulation
-what is the function of the 2 nuclei
In the walls of the 3rd ventricle
Preoptic area
- local change detected
- respond to warming
Posterior area
- distal change detected
- acts as a central controller
Describe the function of muscles in thermoregulation How do -CT -skin, SC signals -preoptic signals affect muscle function
What are the pros and cons of this mechanism
CT falls => increased skeletal muscle tone => spindle reflex activated
Cold signals from skin, SC
Both of these pathways stimulate shivering
Increased preoptic signals (respond to heat) => inhibit shivering
Shivering is energetically expensive, not a good long term mechanism
Describe the function of blood flow in thermoregulation
- AV anastamoses
- Countercurrent exchange
AV anastamoses
- dermal plexus => superficial flow => increased heat loss
- Subcutaneous plexus => deep flow => increased heat retention
Countercurrent exchange
- deep veins flow next to arteries
- when hot => deep veins VC => increased superficial flow
- when cold => superficial veins VC => increased deep flow (receive heat via conc gradient from arteries)
SNS input => VC to increase/decrease heat loss
Describe the function of brown adipose tissue in thermoregulation
Babies cannot shiver
OX PHOS in brown adipose mitochondria can be uncoupled with SNS input
-generate heat without making ATP
Describe the function of horripilation in thermoregulation
SNS input =>arrestor pili contracts => goosebumps
Is a pathetic mechanism in humans
Describe the function of the sweat glands in thermoregulation
-describe the difference between primary and secondary secretions
Primary secretion
-protein free
Secondary secretion at low rates
-salt, water reabsorbed => urea, lactate rich
Secondary secretion at high rates
-salt reabsorbed => very watery secretion
SNS activated, cholinergic
What is the thermoneutral zone
A range of ambient temperatures where VD, VC alone can control CT => BMR stays constant
Describe how the temperature set point can be changed by
- increased skin temp
- decreased skin temp
Increased skin temp => decreased set point
- increased sweating at lower hypothalamic temp
- increased shivering at lower CT
Decreased skin temp => increased set point
- increased sweating at higher hypothalamic temp
- increased shivering at higher CT
What are the adaptations that help us to acclimatize to heat
- increased heat loss
- reduced heat production
Increased heat loss
- behavioural => clothing, housing, exposure
- VD =>apical at TNZ + non apical at higher temps
- sweating from eccrine glands, markedly increased when prolonged
Reduced heat prod
- inactivity, inertia => rest, lower BMR
- food intake reduced => high water content foods preferred
What are the adaptations that help us to acclimatize to cold
- increased heat production
- decreased heat loss
Increased heat production
- voluntary muscle activity
- involuntary muscle activity => increased tone, tremor, shivering (also leads to increased heat loss)
- brown fat metabolism => increased heat without increased ATP
Decreased heat loss
- behvaioural => clothing, housing, exposure
- VC => reduce superficial flow
- horripilation => goosebumps
