Thermoregulation Learning Objectives (L28)

Question 1

What is the risk of a core temp ~40C

Answer 1

Increase risk of denaturing proteins

Question 1

What is the core temperature normal range?

Answer 1

Ideal is 37C +/- 1C (36 - 38C)

Question 2

What is the risk of a core temp ~27C

Answer 2

Increase risk of cardiac arrest

Question 3

What determines the direction of heat transfer?

Answer 3

Temp gradient

Question 4

What determines the rate of heat transfer?

Answer 4

• Conductor (i.e.: air or water, water is faster)
• Size of temp gradient (faster with a larger gradient)
• Body surface area: mass ratio (i.e.: how submerged you are in cold water)

Question 5

What brain structure integrates thermoregulation?

Answer 5

Hypothalamus

Question 6

What are the physiological responses to cold?

Answer 6

Decrease blood flow to skin & extremities
Muscular activity (shivering)
Hormonal secretions (thyroid hormones and adrenaline to raise metabolism)

Question 7

What are the behavioural responses to cold?

Answer 7

Clothing
Muscular activity (shivering)
Change environment (shelter, warmer)
Consume warm food & drinks

Question 8

What is the functional adaptation to being able to increase heat generation without shivering called?

Answer 8

Cold acclimatisation

Question 9

What is the change in observable physiological response for individuals who have acclimated to colder environments? How are they able to do this?

Answer 9

Can sustain lower body body temperatures before shivering occurs.
Mechanism: Increase heat generation without shivering, occurs due to a decrease of blood flow to periphery to conserve heat for core BUT periodically increase blood flow to extremities to reduce risk of cold injury.

Question 10

What is the physiological mechanism that would describe the reason to why you take a breath before diving into a pool?

Answer 10

Diving reflex. It has the greatest CV effects when the subject is holding their breath with their face wetted.

Question 11

What is the diving reflex and why do we need it?

Answer 11

The diving reflex is a set of physiological responses to immersion that overrides the basic homeostatic reflexes. Main aim is to preserve O2 by:
- Shunting blood away from vital organs (via vasoconstriction),
- Induces bradycardia,
- Concentrating blood flow in a heart–brain circuit.

Question 12

What are the physiological responses to heat?

Answer 12

Increase blood flow to skin & extremities
Sweating
Increase breathing (small effect)
Hormonal secretions
– Decrease thyroid hormones
– Increase fluid balance hormones (ADH and aldosterone)

Question 13

What are the behavioural responses to heat?

Answer 13

Clothing
Reduce or alter physical activity (swim, shower)
Change environment (shelter, cooler)
Decrease food intake; intake cool drinks

Question 14

What is the role of the ANS in thermoregulation?

Answer 14

The SNS:
– Vasoconstrict skin vessels in cold
– Vasodilate skin vessels in heat

Question 15

What division of the ANS mediates sweating

Answer 15

SNS

Question 16

What temperature is best for performance in longer-duration sports?

Answer 16

Moderately cold

Question 17

What is the ratio between blood flow to skin and muscle in:

a) hotter environments
b) cooler environments

Answer 17

a) 50/50
b) favours flow to the muscles

Question 18

Where does does the body prioritise blood flow to the most during exercise: muscle or skin

Answer 18

Muscle

Question 19

What environmental factor compromises evaporation (cooling)

Answer 19

High humidity

Question 20

Temperature and what other environmental factor can induce hyperthermia and difficulty regulating fluids?

Answer 20

Humidity

Question 21

How long does it take to acclimate to heat?

Answer 21

Occur in ~ 1 week of exposure to heat

Question 22

What are the physiological adaptations in response to heat acclimation

Answer 22

–
– Increased sweat output
–

Question 23

What is the physiological adaptation in response to exposure to hotter environments that helps in heat conduction and radiation.

Answer 23

Increased blood volume (increased ADH)
Improved skin blood flow (redistribution of blood flow)
Better heat loss

Question 24

What is the physiological adaptation in response to to exposure to hotter environments that helps prevent excess water loss

Answer 24

Lower threshold for sweating (sweat at LOWER body temp)
Sweat less concentrated (lose less electrolytes)
Better heat loss

Question 25

How does HR change as heat stress increases

Answer 25

It increases

Question 26

Higher aerobic fitness levels __________ (improves, reduces) exercise tolerance in heat

Answer 26

Improves

Question 27

Is sweat more or less concentrated compared to blood?

Answer 27

Less

Question 28

During humid, hot environments, what are some major considerations for athletes undertaking longer forms of exercise

Answer 28

• Pre-exercise hydration important
• Fluid loss due to sweat, more so in humid environments
• Electrolytes may aid more rapid rehydration
• Hard to achieve rehydration during exercise

Question 29

By how much (%) should fluid intake exceed fluid loss during exercise in hot, humid environments?

Answer 29

25%

Question 30

Why do children lose heat quicker compared to adults?

Answer 30

Children have large surface area to body mass

Question 31

What are the differences in thermoregulatory capacity between males & females

Answer 31

Little difference

Question 32

What are heat cramps likely due to?

Answer 32

Electrolyte imbalance

Question 33

What causes heat exhaustion?

Answer 33

Low BP (dilation), weak rapid pulse, headache, dizzy

Question 34

What are the components and classification of heat stroke?

Answer 34

Elevated core temperature (> 40.5C)
Absence of sweating (dehydration)