Thermoregulation Flashcards

1
Q
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
A

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-

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2
Q

How would you measure the temperature of the body

What are the pros and cons of each method

A

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

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3
Q
What generates heat?
What proportion of energy is used by
-BMR (awake+sleep)
-Food thermic
-NEAT
-EAT

How is our core temperature maintained

A

Metabolism generates heat

  • BMR => 60%
  • Food thermic => 8%
  • NEAT => 7%
  • EAT => 25%

Skeletal muscle generates heat => lost to maintain CT

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4
Q

Describe these 4 methods of heat transfer

  • radiation
  • convection
  • Conduction
  • Evaporation
A

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
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5
Q

Describe the feedback loop involved in thermoregulation

A

Receptors detect change in temperature
Hypothalamic control center
Sends efferents to effectors

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6
Q

Describe the function of the hypothalamus in thermoregulation
-what is the function of the 2 nuclei

A

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
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7
Q
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

A

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

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8
Q

Describe the function of blood flow in thermoregulation

  • AV anastamoses
  • Countercurrent exchange
A

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

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9
Q

Describe the function of brown adipose tissue in thermoregulation

A

Babies cannot shiver
OX PHOS in brown adipose mitochondria can be uncoupled with SNS input
-generate heat without making ATP

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10
Q

Describe the function of horripilation in thermoregulation

A

SNS input =>arrestor pili contracts => goosebumps

Is a pathetic mechanism in humans

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11
Q

Describe the function of the sweat glands in thermoregulation
-describe the difference between primary and secondary secretions

A

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

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12
Q

What is the thermoneutral zone

A

A range of ambient temperatures where VD, VC alone can control CT => BMR stays constant

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13
Q

Describe how the temperature set point can be changed by

  • increased skin temp
  • decreased skin temp
A

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
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14
Q

What are the adaptations that help us to acclimatize to heat

  • increased heat loss
  • reduced heat production
A

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
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15
Q

What are the adaptations that help us to acclimatize to cold

  • increased heat production
  • decreased heat loss
A

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
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16
Q

What changes would occur in prolonged heat exposure

A

Increased sweating but decreased salt loss

BMR falls

17
Q

What changes would occur in prolonged cold exposure

-why can this be a problem

A

Initially, VC maintains CT => loss of manual dexterity, frostbite

Paradoxical VD
-increased manual dexterity, decreased frostbite risk

Lowered TNZ

  • VD, VC at lower ambient temperatures
  • shiver at lower temps