Thermoregulation

Question 1

Explain how the hypothalamus maintains thermal balance (heat)

Answer 1

Negative feedback loop
1. increased blood temp (small as 0.01C)
2. afferent signals give input to hypothalamus
3. hypothalamus triggers quick response
- vasodilation of blood vessels
- increasing sweat/evaporative heat loss

*quickly trigger reflexes to help conserve or eliminate body heat *

Question 2

What are physical factors that contribute to heat loss?

Answer 2

convection, evaporation, conduction, radiation

Question 3

What are physical factors that contribute to heat gain?

Answer 3

BMI, muscular activity, hormones, thermic effect of food, postural changes, enviroment

Question 4

How does the circulatory system adjust during temperature changes?

Answer 4

1. venous blood vessels dilate to divert warm blood to skin (HR & Q increase) rest*
2. lower SV so higher HR *submaximal intensity
3. maximal Q decreases
4. maintaining skin/muscle blood flow require other tissues to compromise blood supply

Question 5

How is fluid loss during hot-weather exercise calculated?

Answer 5

for every 1pound of weight loss, drink 450mL

Question 6

What is the purpose of fluid replacement & pre-exercise hydration?

Answer 6

purpose:
1. to maintain plasma volume so circulation & sweating can occur
2. increase blood flow to skin for effective cooling
3. most effective defense against heat stress

Question 7

What factors maintain cutaneous blood flow & BP during exertion in heat?

Answer 7

dilation of blood vessels

Question 8

How does cardiac output respond during hot-weather physical activity?

Answer 8

maximal Q decreases (because the increase in HR is not greater than the decrease in SV)

Question 9

How does heart rate respond during hot-weather physical activity?

Answer 9

increases, to adjust for the decrease in SV

Question 10

How does stroke volume respond during hot-weather physical activity?

Answer 10

decreases, because blood is getting directed to skin instead of the core

Question 11

How does acclimatization modify heat tolerance during physical activity?

Answer 11

improves exercise capacity with less discomfort upon subsequent heat exposure
(occurs during 1 week of heat exposure)

• improved cutaneous blood flow
• effective Q distribution
• lower threshold for start of sweating
• increased sweat output
• lower Na concentration of sweat
• lower skin/core temp & HR during exercise

Question 12

How does training modify heat tolerance during physical activity?

Answer 12

1. increases sensitivity/capacity of sweat response
   (sweating begins at lower temp)
2. greater cutaneous blood flow at given internal temp or % of VO2 max

Question 13

How does age & gender modify heat tolerance during physical activity?

Answer 13

age: no differences (young, middle-aged)
children –> sweat less & maintain higher core temp during heat stress (despite more# sweat glands)
- intensity effort should decrease & longer time for acclimatization

gender:
Women sweat less than men
- sweat at higher skin/core temp & produce less sweat (even after acclimatization)
- smaller & relatively larger body surface area per unit mass (favours heat dissipation)

why? greater use of circulatory mechanisms for dissipating heat

Question 14

How does body fat modify heat tolerance during physical activity?

Answer 14

fat increases insulatory capacity of body & limits conduction to periphery
- heat capacity of fat > muscle
- smaller SA to body mass ratio
(limits effectiveness of evaporation)

Question 15

What are the symptoms, causes, and treatments for heat exhaustion?

Answer 15

cause: ineffective circulatory adjustments with depletion of extracellular fluid (plasma volume) from excessive sweating

symptoms:
- nausea, chills, goose bumps, headache

Question 16

What are the symptoms, causes, and treatments for heat stroke?

Answer 16

cause: SERIOUS, failure of heat-regulating mechanisms from excessively high core temp

symptoms:
cessation of sweating, confusion, LOC

Question 17

What are the physiological adjustments to cold stress?

Answer 17

Vascular:
- peripheral blood vessels constrict to redirect warm blood to core

Muscular:
- PA best defence against cold (can sustain core temp as cold as -30C)
- shivering (metabolic heat) 4-5fold increase in heat production

Hormonal:
- Epi/norepi increase heat production
- thyroxine increases resting metabolism (prolonged cold stress)

Question 18

What effect does airway remodelling due to exercise in cold air have?

Answer 18

prolonged exposure to cold can cause inflammation & remodelling of airways

Question 19

How high does metabolism become in elite athletes during intense aerobic activity?

Answer 19

20-25x above resting levels

Question 20

What is conduction?

Answer 20

direct heat transfer from one molecule to another (either gas, liquid, solid)

ex. moving from deep tissues to cooler surfaces
(has to be physically touching?)

Question 21

What does conduction depend on?

Answer 21

1. temperature gradient between skin & surrounding temperature
2. thermal qualities of the surface

Question 22

What is convection?

Answer 22

transferring heat by motion of a gas or liquid across a heated surface

ex. heat is exchanged with the air passing over skin

greater movement = greater rate of exchange

Question 23

What is radiation?

Answer 23

heat waves emitted, that may be absorbed by a cooler body

Question 24

What are the 2 primary methods for eliminating excess body heat?

Answer 24

radiation & convection

Question 25

What is evaporation?

Answer 25

fluid evaporates into gas, heat is lost

*primary way for heat dissipation during exercise

Question 26

What influences evaporation for the body?

Answer 26

1. surface exposed to the environment
   (better if skin is exposed)
2. temperature & relative humidity of ambient air
3. convective air currents about the body

Question 27

What is the result of particular physiological adjustments when exercising in the heat?

Answer 27

increases blood lactate accumulation

1. decreased lactate uptake by liver from reduced hepatic blood flow
2. less muscle catabolism of circulating lactate because heat dissipation diverts Q to periphery

Question 28

What is the impact of fluid loss on the body? (via evaporation)

Answer 28

1. lower plasma volume
2. depressed skin blood flow for given core temperature
3. reduced SV
4. increased HR
5. general deterioration in circulatory & thermoregulatory efficiency in exercise

Question 29

What is the difference between fluid intake & no fluid intake when exercising in the heat?

Answer 29

graph:
no fluids –> body temp increases linearly as exercise continues

with fluids –> body temp will plateau as exercise continues

Question 30

Explain how the hypothalamus maintains thermal balance (cold)

Answer 30

Negative feedback loop
1. blood/skin temp decreased
2. afferent signals trigger hypothalamus
3. hypothalamus quickly responds
- vasoconstriction
- shivering via skeletal muscles
4. body temp increases