Thermoregulation

Question 1

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

Answer 1

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-

Question 2

How would you measure the temperature of the body

What are the pros and cons of each method

Answer 2

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

Question 3

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

How is our core temperature maintained

Answer 3

Metabolism generates heat

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

Skeletal muscle generates heat => lost to maintain CT

Question 4

Describe these 4 methods of heat transfer

• radiation
• convection
• Conduction
• Evaporation

Answer 4

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

Question 5

Describe the feedback loop involved in thermoregulation

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

Describe the function of blood flow in thermoregulation

• AV anastamoses
• Countercurrent exchange

Answer 8

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

Question 9

Describe the function of brown adipose tissue in thermoregulation

Answer 9

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

Question 10

Describe the function of horripilation in thermoregulation

Answer 10

SNS input =>arrestor pili contracts => goosebumps

Is a pathetic mechanism in humans

Question 11

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

Answer 11

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

Question 12

What is the thermoneutral zone

Answer 12

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

Question 13

Describe how the temperature set point can be changed by

• increased skin temp
• decreased skin temp

Answer 13

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

Question 14

What are the adaptations that help us to acclimatize to heat

• increased heat loss
• reduced heat production

Answer 14

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

Question 15

What are the adaptations that help us to acclimatize to cold

• increased heat production
• decreased heat loss

Answer 15

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

Question 16

What changes would occur in prolonged heat exposure

Answer 16

Increased sweating but decreased salt loss

BMR falls

Question 17

What changes would occur in prolonged cold exposure

-why can this be a problem

Answer 17

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