Week 8 - Thermoregulation and thermal stress Flashcards

1
Q

What is our normal resting body core temperature?

A

36.5-37.5 degrees Celsius
- Fluctuation throughout the day

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2
Q

In the heat, core temperature can safely increase up to .. degrees Celsius?

A

40 degrees Celsius

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3
Q

In the cold, core temperature can safely drop to .. degrees Celsius?

A

35 degrees Celsius

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4
Q

Define core temperature.

A

defined as temperature of the hypothalamus, the thermoregulator centre of the body.

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5
Q

How can core temperature be assessed?

A
  • Oesophageal temperature
  • Rectal temperature
  • Stomach temperature (swallowed telemetry pill)
  • Oral temperature
  • Tympanic temperature
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6
Q

a) Skin temperature
b) Cool mean skin temp
c) warm mean skin temp
d) hot mean skin temp

A

32-35 degrees Celsius
<30
30-34.9
>35

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7
Q

What does the homeostatic maintenance of body temperature require?

A

the operation of temperature sensors (peripheral and central thermoreceptors) and regulated effectors (adrenal medulla, sweat glands, skin arterioles, skeletal muscles).

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8
Q

Describe physiological control of thermoregulation when body temperature INCREASES.

A

Blood vessels dilates
Sweat glands secrete fluid
–> heat is loss

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9
Q

Describe physiological control of thermoregulation when body temperature DECREASES.

A

Blood vessels constrict
Sweat glands do not secrete fluid
—> Heat is conserved

Shivering generates heat
–> heat is generated

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10
Q

Physiological mechanisms of heat loss

A

Blood reaching the skin (vasodilation)
Sweating

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11
Q

Physiological mechanisms of heat conservation/production

A

Shivering thermogenesis
Voluntary muscular activity
Non-shivering thermogenesis

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12
Q

Heat exchange between the body and environment governed by biophysical properties. What are biophysical properties dictated by?

A

the surrounding temperature, humidity and air motion, sky and ground radiation + clothing

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13
Q

What is the most challenging environment for exercise? Why?

A

Hot and humid - we cannot evaporate sweat from our skin.

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14
Q

We gain/lose heat chiefly through our…

A

shell/skin

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15
Q

Is skin temperature regulated?

A

NO - unlike core temperature it’s not regulated and it varies across the body in response to thermal environment.

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16
Q

What is our most powerful means of regulating body temperature?

A

behavioural responses

17
Q

Why does core temperature increase when performing aerobic exercise in a hot environment?

A

Increase demand on heat loss mechanisms (increase skin blood flow and sweating).

But in hot environments, we get a reduced gradient between core and skin. Therefore, core temp increases as we can’t offload the heat as well as usual.

18
Q

How does dehydration (loss of body water) influence exercise performance in the heat?

A

Exacerbates heat stress impacts.

It decreases sweat rate (needs to keep body water circulating in the blood) and decreases plasma volume.
Further ↓ cardiac output, maximal oxygen uptake, muscle strength and work capacity.

19
Q

Why is prolonged high-intensity exercise impaired by a hot environment?

A

Competing regulatory demands for blood flow between thermoregulation, working muscles and CNS.

Heart-related changes (Incr. HR, reduced SV due to redistribution of blood) in skeletal muscle function and metabolism.

20
Q

What is the most rapid way to lower body temperature?

A

cold water immersion

21
Q

Identify methods that mitigate the impact of heat stress:
a) Before exercise
b) Immediately before exercise
c) During exercise

A

a) Heat acclimation and aerobic training
b) Pre-cooling, hydration status
c) Hydration, clothing, cooling

22
Q

Identify acclimatization responses

A
  • Improved cutaneous blood flow (to the skin)
  • Lower threshold for start of sweating (evaporative cooling begins earlier)
  • Lower skin and core temperatures and heart rate for standard exercise (frees greater CO to active muscle)
  • Effective distribution of cardiac output (skin and muscle)
  • Increased sweat output (maximizes evaporative cooling)
23
Q

Hypothermia

A

core temperature below 35 degrees Celsius
* 2°C drop associated with maximal shivering
* 4°C drop associated with ataxia and apathy
* 6°C drop associated with unconsciousness
* Further drop associated with ventricular fibrillation, reduced brain blood flow,
asystole, death

24
Q

How does cold water influence exercise performance (swimming)?

A

Due to shivering, oxygen consumption is higher in cold
water during sub-maximal exercise but reduced during maximal exercise.

25
Q

Describe the physiological adaptations of cold acclimatization.

A
  • Increased non-shivering thermogenesis: results in lower skin temperature at which shivering begins.
  • Improved peripheral blood flow: ability to prevent large decreases in skin temperature (hand and foot temp) during cold exposure improved.
  • Improved ability to sleep in the cold: due to reduced shivering.
26
Q

Identify physiological responses to exercise in the cold.

A

1) Reduced skin blood flow: peripheral vasoconstriction

2) Increased submaximal V02: greater heat loss

3) Increased ventilation during submaximal exercise: increase sympathetic stimulation

4) Increased lactate concentration: increases carb metabolism

5) Lower lipid mobilization: reduced blood flow to adipocytes

27
Q

How is endurance exercise impaired in hot and humid environments?

A

1) Accelerated muscle fatigue
2) Central NS dysfunction
3) CV dysfunction

28
Q

During exercise, what % of energy produced is released as heat?

A

70-80%

29
Q

What does an increase in body core temperature typically result in?

A

cutaneous vasodilation and sweating