Thermoregulation

Question 1

Heat gain factors

Answer 1

BMR 
Muscular Activity 
Hormones 
Thermic effect of food 
Postural changes of the environment

Question 2

Heat loss factors (4)

Answer 2

Radiation
Conduction
Convection
Evaporation

Question 3

Hypothalamic Temperature Regulation: What is it and how is it activated (2)

Answer 3

Acts as thermostat set and regulated at 37°C ±1°C
initiates responses to protect from gain or loss of heat

CANNOT TURN OFF HEAT, initiates responses to protect from gain or loss of heat

Activation of heat-regulating mechanisms:

1. Thermal receptors in skin =input to central control center
2. Changes in Tblood perfusing hypothalamus directly stimulate central control centre

Question 4

Heat Gain Factors (6)

Answer 4

BMR 
Muscular Activity 
Hormones 
Thermic effect of food 
Postural changes 
Environment

Question 5

Increased Body temperature during exercise

Answer 5

Increase in body temperature with work rate

Linear across wide range of temperatures

Linear for both arm and leg exercises

Temperature proportional to active muscle mass

Question 6

Effects of Clothing on thermoregulation (6)

Answer 6

1. Wind Speed: Higher speed disturbs zone of insulation
2. Body movements: Moving disturbs zone of insulation
3. Chimney Effect: Loosely hanging clothing ventilates trapped air layers away from body
4. Bellows Effect: vigorous body movements increase ventilation of air layers that conserve body heat
5. Water vapor transfer: clothes resist water vapor exit
6. Permeation efficiency factor: how well clothing absorbs liquid by capillary action

Question 7

Football uniforms

Answer 7

Football equipment and clothing seal off 50% of body from evaporative cooling benefits
-Football gear exacerbates increase in rectal and skin temp with exercise

Question 8

Is ear temp a good measurement of core temp

Answer 8

Ear temp generally measures lower than actual core temperature.

Question 9

Effect of Ambient Temperature (3)

Answer 9

1. Heat production remains constant
2. Lower convective and radiant heat loss
3. Higher evaporative loss

Question 10

Evaporation

Answer 10

In order for heat to be lost by sweat it MUST evaporate

Wiping sweat is wastful and innefective

Question 11

Three Factors influence total amount of sweat vaporized from skin and/or pulmonary surfaces

Answer 11

1. Surface exposed to environment
2. Temperature and relative humidity of ambient air
3. Convective air currents about the body

Question 12

Most important factor determining effectiveness of evaporative heat loss

Answer 12

Ratio of water in ambient air (at a given temperature) to total quantity of moisture that air could contain.

Question 13

Sweat Production & Electrolyte Loss

Answer 13

1. Sodium (Dominant): Loss will be noticed in kidneys, which will affect nerve transmission, muscle activation and blood volumes
2. Potassium (Limited)
3. Magnesium

Question 14

Pathway Heat takes to escape

Answer 14

Tissues -> Skin -> Blood -> Environment

Question 15

Fatigue and Core Temperature

Answer 15

Generally coincides with core temperatures between 38 to 40 C

Impairs muscle activation from high brain temperature

Decreases central drive to exercise

Question 16

Impaired exercise performance with inefficient thermoregulation

Answer 16

Fluid and electrolyte loss
Metabolic changes

Impairs ability to deliver glucose and fatty acids

Question 17

Water Loss in heat

Answer 17

Moderate exercise > 1 hour = 0.5-1.0 L sweat loss

Question 18

Such fluid loss coincides with (5)

Answer 18

Fluid loss of 2% body mass adversely affects exercise

1. Lower plasma volume
2. Depressed skin blood flow for a given core temperature 3. Reduced stroke volume
3. Increased near-compensatory heart rate
4. General deterioration in circulatory and thermoregulatory efficiency in exercise

Question 19

Mechanisms contributing to dehydration-mediated physical performance degradation:

Answer 19

1. Augmented hyperthermia
2. Increased cardiovascular strain
3. Altered metabolic & central nervous system functions
4. Increased perception of effort (RPE)

Question 20

Factors that Modify Heat tolerance

Answer 20

1. Acclimatization
2. Trainingstatus
3. Age
4. Gender
5. Bodyfatlevel

Question 21

Acclimatization Response and its effects: Improved cutaneous blood flow

Answer 21

Transports metabolic heat from deep tissues to shell

Question 22

Acclimatization Response and its effects: Effective distribution of cardiac output

Answer 22

Appropriate circulation to skin and muscles to meet demands of metabolism and thermoregulation; greater blood pressure stability during exercise

Question 23

Acclimatization Response and its effects: Lowered threshold for start of sweating

Answer 23

Evaporative cooling begins early in exercise

Question 24

Acclimatization Response and its effects: More effective distribution of sweat over skin surface

Answer 24

Optimum use of effective body surface for evaporative cooling

Question 25

Acclimatization Response and its effects: Increased sweat output

Answer 25

Maximizes evaporative cooling

Question 26

Acclimatization Response and its effects: Lowered salt concentration of sweat

Answer 26

Dilute sweat preserves electrolytes in extracellular fluid

Question 27

Acclimatization Response and its effects: Lower skin and core temperatures and heart rate for standard exercise

Answer 27

Frees greater proportion of cardiac output to the active muscles

Question 28

Acclimatization Response and its effects: Less reliance on carbohydrate catabolism during exercise

Answer 28

Carbohydrate sparing

Question 29

Physical Activity in the Cold

Answer 29

``` Chronic exertional fatigue Sleep loss Inadequate nourishment Reduced tissue insulation Depressed shivering heat production ```

Question 30

Fat and Physiologic Function in the Cold

Answer 30

Successful ocean swimmers possess large amount of subcutaneous fat than highly trained non ocean swimmers Additional Fat increases effective insulation in cold water

Question 31

Cold Stress and Children

Answer 31

A child’s large body surface area-to-mass ratio facilitates heat loss in a warm environment but becomes a liability during cold stress because body heat dissipates rapidly Rely on two mechanisms to compensate for their relatively large surface area-to-mass ratio: – Augmented energy metabolism – More effective peripheral vasoconstriction in limbs

Question 32

Cold Acclimatization

Answer 32

Humans adapt poorly to long-term cold exposure compared to prolonged heat exposure ``` Adaptations: Hand and feet blood flow can increase Shivering occurs at lower body temp Improved ability to sleep in the cold Changes in peripheral blood flow distribution ```

Question 33

Predisposing factors to frost bite

Answer 33

``` Alcohol Use Low physical fitness Fatigue Dehydration Poor peripheral circulation ```