Exercise and Thermal Stress

Question 1

What does body core temperature mean?

Answer 1

37 degrees and the temperature of the brain, abdominal and thoracic organs. Temp of blood perfusing the brain

Question 2

Where are the central thermoreceptors located and what is there mechanism of action?

Answer 2

In the hypothalamus and other brain areas. Neurones firing that are dependent on the temperature, higher the temperature more APs fired. Is a 37degree baseline reading

Question 3

What is forced convection?

Answer 3

Movement through the environment, air moving past the skin surface and being lost

Question 4

What is conduction?

Answer 4

The direct transfer of heat to objects in direct contact with the skin

Question 5

What is convection?

Answer 5

When heated, air or water molecules rise and are replaced by cooler air/water.

Question 6

What is radiation?

Answer 6

The transfer of heat from he skin, via electromagnetic waves, to surrounding objects at a lower temperature.

Question 7

What is the latent heat of the evaporation of water?

Answer 7

2.4kJ.g-1

Question 8

What must sweat do for it to be effective?

Answer 8

Evaporate from the skin surface

Question 9

What is the efficiency of converting chemical energy (ATP) to mechanical energy?

Answer 9

20-30%

Question 10

What is the specific heat capacity of human tissue?

Answer 10

3.5kJ.kg.degreesC-1

Question 11

What does high levels of humidity do?

Answer 11

Inhibit the evaporation of sweat and sweat doesn’t cool unless it evaporates

Question 12

What type of clothing should be wore with exercise at high temperatures?

Answer 12

More clothing worn the less sweat that can evaporate.
Minimal clothes should be worn, should be loose weaved to allow sweat to pass and light coloured to reflect suns radio heat gain.

Question 13

Where are arteriovenous anastomoses located?

Answer 13

Mainly in the arteriovenous anastomoses - fingers, toes, ears, nose, etc

Question 14

What are arteriovenous anastomoses?

Answer 14

Low resistance shunts from arterioles to venues, dilation of these increase blood flow

Question 15

What happens to cardiac output from a cool to a hot environment?

Answer 15

CO doubles

Question 16

What cutaneous blood flow can be reached at maximum vasodilation?

Answer 16

greater than 5l.min

20-30 fold increase from skin blood flow at the thermoneutral state

Question 17

What are the two types of sweat glands called?

Answer 17

Apocrine and eccrine

Question 18

Where are apocrine sweat glands located?

Answer 18

In the auxiliary and pubic regions and they are not thermoregulatory

Question 19

Hoe many eccrine sweat glands are distributed over the body surface?

Answer 19

2-3million

Question 20

How are eccrine sweat glands stimulated to secrete sweat?

Answer 20

By cholinergic sympathetic nerve fibres (sudomotor nerves) and via circulating catecholamines (adrenaline and noradrenaline)

Question 21

What is the ‘primary sweat’ that the eccrine glands secrete?

Answer 21

Effectively protein free, hypotonic plasma filtrate gets modified along its passage of the sweat duct

Question 22

How is the ‘primary sweat’ modified along its passage along the sweat duct?

Answer 22

Reabsorption of electrolytes (mainly Na+ and Cl-) making the final sweat more hypotonic

Question 23

What happens to the sweat as the sweat rate increases?

Answer 23

There is less time for reabsorption along the sweat duct and the ionic concentration in the final sweat increases

Question 24

Do males or females have a higher sweat rate?

Answer 24

Males can sustain higher sweat rates

Question 25

What is maximal sweat rate determined by?

Answer 25

Many factors

• fitness (fitter people have higher sweat rates)
• gender
• degree of acclimatisation

Question 26

What is cardiovascular drift?

Answer 26

As exercise in the heat progresses, the central blood volume continues to fall (as a result of fluid losses n the sweat and pooling of blood in the venous vessels and cuteness vascular beds). This results in a decrease in SV and a steady increase in HR to maintain CO. But once maximal HR is reached something has to give.

Question 27

How long do athletes need to acclimatise to the heat?

Answer 27

10-14 day period by exercising i the heat fro 30-90minutes per day

Question 28

How does acclimatisation to the heat occur?

Answer 28

• causes a reduction in how much the core temperature and HR rise
• increased sweat rate for any given core temperature
• causes a lower temperature threshold for the onset of sweating
• increased plasma volume (due to increase production of albumin) helps preserve SV
• decreased skin blood flow

Question 29

What are the characteristics of heat cramps?

Answer 29

• painful involuntary contractions of skeletal muscles - particularly leg and abdominal muscles
• caused by prolonged, excessive salt and/or water losses, resulting in disturbances of fluid and electrolyte levels.
• may occur at normal, or slightly elevated, body core temperatures, and may be associated with fatigue, giddiness and gastric upset

Question 30

How are heat cramps treated?

Answer 30

Isotonic saline (oral or i.v) and the massaging of the affected muscles

Question 31

What are the symptoms of heat exhaustion?

Answer 31

weak pulse, low blood pressure, light-headedness, nausea, vomiting, fainting, restlessness
- caused by blood pools in the dilated peripheral vessels, dramatically reducing central blood volume compromising CO. increased heat production and impeded heat loss.

Question 32

Treatment for heat exhaustion

Answer 32

The casualty should be removed from the hot environment (if possible), cooled by stripping, fanning, spraying with cold water, etc. and given appropriate fluid replacement (I.V. if necessary)
hyperventilation stopped by breathing into a paper bag

Question 33

Above what temperature does heat stoke occur?

Answer 33

41 degrees C

Question 34

What is heat stoke?

Answer 34

Essentially a failure of thermoregulatory mechanisms brought about by excessively high body temperatures

Question 35

Heat stroke symptoms?

Answer 35

Symptoms appear suddenly and progress rapidly: weakness, headache, dizziness, confusion, staggering gait, rapid pulse and respiration, convulsions, projectile vomiting, circulatory collapse, organ failure, coma and death.

Question 36

Treatment of hyperventilation

Answer 36

Casualty must be removed from the heat as a matter of urgency and actively cooled (ice bath, drenching, stripping, fanning, etc.)
I.V. rehydration is essential: isotonic saline containing 5% glucose is ideal