Thermoregulation 2

Question 1

Environmental heat strain and exercise

Answer 1

• Strain - collection of environmental factors
• Stress - bodies response
• Three factors - ambient temperature, ambient humidity and wind velocity
• As temperature increases heat strain increases - exponential (when temp exceeds 15oC)
• More linear relationship between humidity and heat strain
  
  • Humidity - Content of water in the air
• Both humidity and temperature drive heat strain up
• As you increase wind velocity, increases heat loss (beneficial in warmer climates, not so much in colder climates)

Question 2

Ambient temperature effects on exercise responses

• Endurance
• Skin temp
• Core temp

Answer 2

Study

• Took 8 male subjects - exercised at 70% VO2max at different temperatures - moderate to high intensity
• Endurance was highest at 11 C
• Ambient has a very large effect on endurance
• At neural temperature (21 degrees), skin temp fell immediately at the start of exercise and rebounds back up.
• Skin temp increases at the start of exercise at ambient temp of 31 degrees and then stabilises
• Core temperatures increases regardless of ambient temperature and stabilises at 4, 11, and 21 degrees

Question 3

Ambient humidity effects in exercise response

• Core temp
• Skim temp
• Endurance

Answer 3

• Chamber temperature - 30 degrees
• Air velocity - 1 m/s
• 8 male subjects
• Exercising at 70% VO2max
• Humidity levels: 24%, 40%, 60%, & 80%
• 24% - core temp tends to be slightly lower
• 40%, 60% & 80% - core temp is higher but there is a progressive reduction in how long they can maintain exercise
• As the humidity increases the skin temp increases
• As humidity increases the endurance decreases (endurance in impaired progressively from low levels of 24% to 80%)

Question 4

Physics of environment effects on core temperature

• convection
• Humidity and sweat

HINT: gradient

Answer 4

• Gradient between the skin and core is 5 degrees
• Convection - transfer of heat from the core to the skin (surface) via blood flow
• You can only lose heat to the surroundings if the ambient temperature is less than the skin temperature (positive gradient)
• If ambient temp is higher than skin temp, we absorb heat
• The rate at which sweat vaporises depends on humidity ( has to be less than 100%)
• The lower the humidity the higher the rate of sweat vaporisation.

Question 5

Heat Acclimatisation

Answer 5

With heat acclimatisation, core temperature raises less steeply and stabilizes and skin temperature raises less steeply, stabilises and then comes back down. sweat sensitivity is higher

45 degree heat exposure: sustain exercise for 4 hours, lower core temperature, and skin temperature. significantly greater sweating sensitivity

Question 6

Cell homeostasis to systemic regulation

Answer 6

Homeostasis - keeping the environment of the cell under the conditions in which that cell can operate most effectively

Question 7

Thermostat Model I

Answer 7

Our bodies regulates itself to maintain core temperature

Question 8

Thermostat Model II

Answer 8

• Set-point temperature is the core temperature
• The body will respond to variations in core temperature
• The main region that controls the set-point temperature is the hypothalamus

Less than set point -> Decrease heat loss & increased heat gain ->

More than set point -> Increased heat loss

Question 9

Thermoregulation

Answer 9

• Metabolism: increases when ambient temp is less than 18 degrees
• Sweating: increases when ambient temperature is 30 degrees
• Skin blood flow: Increases when ambient temperature is 30 degrees

Question 10

Temperature control mechanism

• controller
• sensor
• effectors

Answer 10

• Neural controller - hypothalamus & preoptic nucleus
• Temperature sensors
  
  • Cerebral blood temperature (the blood the hypothalamus is sensing) (core temp)
  • Deep Nerve afferents - lie in deep tissue (thorax and abdomen) (core temp)
  • Skin nerve afferent - respond to changes in skin temperature
• Temperature effectors (bring about the adjustment in temperature)
  
  • Sweating & skin blood flow

Question 11

Temperature and water

Answer 11

• Anterior nucleus - coping in the heat
• Posterior nucleus - coping in the cold
• Paraventricular and supraoptic nucleii - they receive information about the water content in the body and they also influence a response to try and either conserve water or get rid of water
• Close relationship between thermoregulation and water balance
• They work as a unit

Question 12

Threshold and sensitivities

• Cutaneous vasodilation
• Sweating

Answer 12

• Cutaneous vasodilation - dilation of blood vessels in the skin
  
  • If you increase core temp you increase vasodilation and therefore increase blood flow
  • Threshold - 37 and therefore becomes sensitive after 37
• Sweating
  
  • Any temp less than normal core temp does not trigger sweating
  • Just above core temperature when sweating starts and increases as a function of temperature

Question 13

Adaptation

• Training
• Heat acclimation
• Control

Answer 13

• Training & heat acclimation - increase in sensitivity and decreases threshold (sweating occurs earlier)
• Heat acclimation - threshold is lower than both training and control - 37 degrees
  Control is 37.5 (dramatic increase in sweating and skin blood flow)