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Kin 200 > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

What is thermoregulation?

A

Thermoregulation is the body’s ability to resist changes in internal (core) temperature during exercise.

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2
Q

Where is the primary control center for thermoregulation located?

A

The hypothalamus, which acts as the body’s thermostat. It controls mechanisms that keep core temperature around 37 ± 1 °C.

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3
Q

What are the sources of input for the hypothalamus during thermoregulation?

A
  • The hypothalamus is very sensitive to small changes in blood temperature.
  • Thermal receptors in the skin provide an early warning system.
  • Deep neural receptors in the abdomen and great veins also sense internal temperature changes.
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4
Q

What factors cause normal body temperature fluctuations?

A

Body temperature normally fluctuates throughout the day and in response to several factors, including:
* Physical activity
* Emotions
* Hormones
* Food and digestion
* General metabolism
* Ambient temperature

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5
Q

What is the diurnal fluctuation of body temperature?

A

Body temperature exhibits a daily (24-hour) cycle with the lowest temperatures occurring during sleep and higher temperatures when awake.

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6
Q

Define thermal balance

A

Thermal balance is the regulation of heat loss to control body temperature at rest, during exercise, and in response to environmental conditions

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7
Q

What are the types of thermal receptors and their locations?

A
  • Central receptors: Located in the hypothalamus.
  • Peripheral receptors: Skin receptors that detect cold and warm temperatures.
  • Deep neural receptors: Located in the abdomen and great veins
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8
Q

What is the body’s response to heat?

A

To maintain core temperature, the body responds to heat with:
* Peripheral vasodilation: Widening of blood vessels in the skin to increase blood flow and promote heat loss.
* Increased sweating: Evaporation of sweat helps cool the body.
* Conscious actions: Choosing lighter clothing, seeking shade.
* Acclimatization: Physiological adaptations that occur over time with repeated heat exposure.

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9
Q

What is the body’s response to cold?

A

To maintain core temperature, the body responds to cold with:
* Peripheral vasoconstriction: Narrowing of blood vessels in the skin to reduce blood flow and heat loss.
* Shivering and non-shivering thermogenesis: Increases metabolic heat production.
* Piloerection: “Goosebumps” help trap a layer of warm air near the skin.
* Conscious actions: Wearing warm clothing, curling up.
* Acclimatization: Physiological adaptations that occur over time with repeated cold exposure

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10
Q

What is the most valid way to measure core temperature?

A

Rectal temperature is considered the most valid measure of core temperature

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11
Q

Why are oral and tympanic temperature measurements typically lower than rectal temperature?

A

Oral temperature is influenced by breathing and respiratory evaporative cooling, while tympanic temperature, although more accurate than oral, is still slightly lower than rectal temperature

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12
Q

What are other methods for measuring body temperature?

A
  • Telemetric thermal pills: Swallowed pills that transmit temperature data but are expensive.
  • Temperature control suits: Circulate fluid to manipulate skin and/or core temperature.
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13
Q

How is skin temperature measured?

A

Skin temperature is typically measured using thermistors. The accuracy of the measurement can vary depending on the location, exposure, and movement of the skin.

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14
Q

Describe radiation as a heat exchange mechanism.

A

Radiation is the transfer of heat between two objects without direct contact via energy waves (usually electromagnetic). All objects emit thermal radiation. The body can lose heat to cooler surroundings through radiation or gain heat from hotter objects

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15
Q

Approximately how much heat exchange at rest occurs due to radiation?

A

Radiation accounts for around 60% of heat exchange at rest.

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16
Q

Describe conduction as a heat exchange mechanism

A

Conduction is the transfer of heat between two objects of different temperatures that are in direct contact, with no movement between them

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17
Q

Give examples of conduction in thermoregulation

A
  • Cooling vest worn on the chest
  • Ice application to a joint
  • Sitting still in a hot tub
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18
Q

How much heat exchange at rest is due to conduction?

A

Conduction accounts for about 3% of heat exchange at rest

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19
Q

Describe convection as a heat exchange mechanism

A
  • Convection is the transfer of heat from one place to another by the motion of a heated substance, such as air or water.
  • For example, air flowing over the skin removes heat
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20
Q

What factors influence the amount of heat loss through convection?

A

The amount of heat loss via convection is directly related to the velocity and temperature of the air flow

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21
Q

How much heat exchange at rest is due to convection?

A

Convection accounts for approximately 12% of heat exchange at rest

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22
Q

How does being in water affect convective heat loss?

A

Heat loss through convection is 2-4 times greater when swimming in cool to cold water, and heat gain is increased in a hot tub

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23
Q

Describe evaporation as a heat exchange mechanism

A

Evaporation is the transfer of heat that occurs when a liquid changes into a gas or vapor

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24
Q

What is the primary method of heat loss during exercise?

A

Evaporation of sweat is the primary way the body loses heat during exercise

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25
Q

What is “insensible” evaporation, and how much heat loss does it account for at room temperature?

A

Insensible evaporation is evaporation that occurs unnoticed, from the skin and respiratory tract. It accounts for 25% of heat loss at room temperature

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26
Q

What factors can limit the effectiveness of evaporative cooling?

A

The effectiveness of evaporative cooling can be limited by:
* Sweat dripping off the body without evaporating (e.g., during indoor exercise).
* High humidity, as the air is already saturated with water vapor.

27
Q

What are the sources of heat gain for the body?

A

The body gains heat from metabolic heat production and the environment

28
Q

What is the critical core temperature above which heat gain can be fatal?

A

A core temperature above 42°C can be fatal. Temperatures above 44°C can cause proteins in the body to denature (breakdown), leading to nerve tissue breakdown, hemorrhage, and organ failure

29
Q

Define hyperthermia

A

Hyperthermia is defined as a core temperature above 41°C

30
Q

What are the key physiological challenges during exercise in the heat?

A
  • Maintaining oxygen delivery to working muscles: This requires adequate blood flow.
  • Increasing heat transfer to the skin for cooling: This also requires blood flow.
  • Maintaining blood pressure: This can become difficult when blood flow is being directed to both the muscles and the skin
31
Q

What happens to blood flow during prolonged exercise in the heat?

A
  • Blood flow is shunted away from non-essential tissues.
  • Blood flow to active muscles is prioritized, potentially at the expense of blood flow to the periphery (skin)
32
Q

What are potential consequences of impaired blood flow to the periphery during exercise in the heat?

A

Reduced blood flow to the periphery can lead to:
* Exercise-induced hyperthermia
* Heat stress
* Heat exhaustion
* Heat stroke

33
Q

Define cardiovascular drift

A

Cardiovascular drift is a phenomenon characterized by a continuous, time-dependent change in some cardiovascular responses after approximately 10 minutes of prolonged, moderate-intensity exercise (50-75% VO2max) in a neutral or warm environment

34
Q

How does dehydration affect cardiovascular drift?

A

Dehydration exacerbates cardiovascular drift and involves different regulatory mechanisms compared to cardiovascular drift without dehydration

35
Q

Explain the classical theory of cardiovascular drift (without dehydration)

A
  • Increased demand for skin blood flow leads to a redistribution of cardiac output.
  • Less blood returns to the heart, decreasing preload, which in turn decreases stroke volume (SV).
  • Heart rate (HR) increases to compensate for the decline in SV and maintain cardiac output
36
Q

Explain the modern theory of cardiovascular drift (without dehydration)

A
  • The decline in SV is primarily due to increased forearm blood flow (FBF).
  • Increased sympathetic nervous system (SNS) activity drives HR higher.
  • Reduced filling time further contributes to the decrease in SV.
  • HR increases in response to the decline in preload and SV.
37
Q

How does dehydration affect cardiovascular drift?

A
  • Increased SNS activity increases HR and reduces filling time.
  • Dehydration further reduces preload, decreasing SV.
  • Increased SNS activity vasoconstricts skin blood vessels, reducing cutaneous blood flow and heat dissipation.
  • Preventing dehydration is crucial during prolonged exercise in the heat.
38
Q

Do older adults respond differently to exercise in the heat compared to younger adults?

A

Yes. Older adults have a number of physiological changes that make them more susceptible to heat stress, including:
* Reduced circulation
* Reduced sweat gland efficiency
* Possible deconditioning
* Potential presence of degenerative diseases
* Possible use of medications that can affect thermoregulation
* Lower cognitive awareness of heat stress
* Tendency to overdress

39
Q

Do children respond differently to exercise in the heat compared to adults?

A

Yes. Children have several physiological differences that can increase their risk of heat stress, including:
* Higher relative energy expenditure during walking/running, leading to increased heat production.
* Lower sweat rates at rest and during exercise due to immature sweating control mechanisms.
* Lower cardiac output at any given metabolic level, reducing their capacity for heat transfer from the core to the periphery.

40
Q

Are there sex differences in response to exercise in the heat?

A

Yes, but overall tolerance is similar. While women have physiological differences that could make them more susceptible to heat stress, they generally tolerate exercise in the heat as well as men. These differences include:
* Slower initiation of sweating and lower sweat rate despite having more sweat glands per skin area.
* Higher body fat percentage, which may increase heat storage.
* Larger body surface area to mass ratio, which favors cooling.
* Lower dehydration levels during exercise in the heat.

41
Q

List some practical considerations for exercising in the heat.

A
  • Avoid prolonged exercise in hot and/or humid conditions.
  • Wear light-colored, well-ventilated clothing to reflect heat and promote airflow.
  • Consider clothing with wicking properties to help with sweat evaporation.
  • Stay hydrated but avoid overdrinking during exercise.
  • Be aware of the signs and symptoms of heat illness.
  • Reduce exercise intensity and duration in extreme heat.
  • Acclimatize to the heat gradually.
  • Consider using cooling devices.
42
Q

Define acclimatization

A

Acclimatization refers to the physiological adjustments the body makes in response to continuous exposure to various climatic conditions

43
Q

Describe the process of acclimatization to heat

A
  • Begins within 1-4 days and is fully complete within 10-24 days (~1 month) of exposure.
  • Involves an improved circulatory response with enhanced vasodilation of surface vessels and better shunting of blood to the skin.
  • Improves the sweating response, causing it to begin earlier and increase output, while reducing body water and electrolyte loss. This is due to alterations in the hormonal response of ADH (which promotes water reabsorption) and aldosterone (which promotes sodium reabsorption).
44
Q

In what situations can significant heat loss occur?

A

Heat loss can occur due to:
* Exercising in a cold environment
* Wind chill
* Inadequate clothing
* Cold water swims
* Participation in winter sports

45
Q

What is the critical core temperature below which heat loss can be fatal?

A

A core temperature below 30°C can be fatal. [21] Below 29°C, the hypothalamus loses its ability to regulate core temperature, which can lead to circulatory and heart failure

46
Q

Define hypothermia

A

Hypothermia is diagnosed when core temperature falls below 35°C

47
Q

Why is exercise-induced hypothermia rare?

A

Exercise-induced hypothermia is uncommon because individuals typically take precautions such as wearing appropriate clothing and respecting temperature and wind chill guidelines.

48
Q

What is the biggest issue associated with exercise in the cold?

A

Frostbite, particularly in the extremities.

49
Q

Describe non-shivering thermogenesis

A

Non-shivering thermogenesis is an increase in metabolic heat production at rest caused by the sympathetic nervous system’s release of epinephrine and thyroxin hormones. This process “uncouples” oxidative phosphorylation, releasing heat instead of producing ATP

50
Q

Describe peripheral vasoconstriction

A

Peripheral vasoconstriction is the narrowing of blood vessels in the skin, which helps retain heat in the core but can lead to colder peripheral tissues (e.g., cold feet)

51
Q

What is involuntary shivering, and how does it contribute to thermoregulation in the cold?

A

Involuntary shivering is a rapid, rhythmic contraction of skeletal muscles initiated by the central nervous system to increase metabolic heat production

52
Q

How do “goose bumps” help regulate body temperature in the cold?

A

“Goose bumps,” or piloerection, occur when tiny muscles attached to hair follicles contract, causing the hairs to stand erect. This attempts to trap a layer of warm air near the skin surface, providing insulation

53
Q

How does cold water affect heat loss compared to air?

A

Cold water increases heat transfer 2 to 4 times more than air

54
Q

How does exercise in cold water affect energy expenditure?

A

Exercise in cold water leads to higher energy expenditure during submaximal exercise as the body tries to reduce heat loss, likely through non-shivering thermogenesis.

55
Q

How does core temperature affect VO2max in the cold?

A

VO2max decreases by 5 to 6% for every 1°C drop in core temperature. This can impact athletic performance in cold environments

56
Q

Why does exercise in the cold generally lead to an increase in energy expenditure?

A

Energy expenditure typically increases during exercise in the cold due to the body’s mechanisms for conserving and/or producing heat

57
Q

Describe the process of acclimatization to cold

A
  • Changes begin within approximately 7 days and become mostly complete within one month.
  • Increased non-shivering thermogenesis, mainly due to increased thyroxin hormone stimulation of metabolism.
  • Reduced mean skin temperature at which shivering begins (i.e., the skin must be colder to trigger shivering).
  • Increased mean skin temperature of the hands, feet, and face due to intermittent vasodilation in these areas
58
Q

Do older adults respond differently to cold exposure compared to younger adults?

A

Yes. Older adults are more susceptible to cold stress due to:
* Loss of muscle mass
* Poor circulatory control
* Reduced shivering capacity
* Reduced hypothalamic control
* Presence of degenerative diseases
* Use of medications that can affect thermoregulation
* Lower cognitive awareness of cold stress

59
Q

Do children respond differently to cold exposure compared to adults?

A

Yes. Children are more vulnerable to cold stress due to:
Greater surface area to mass ratio, leading to greater heat loss potential.
Less subcutaneous fat, providing less insulation.
Lower capacity for heat production.
Earlier onset of shivering.

60
Q

Are there sex differences in response to exercise in the cold?

A

Yes, but overall tolerance is similar. Women generally tolerate exercise in the cold similarly to men, and some researchers suggest they may even tolerate it better. Physiological differences include:
* Greater peripheral vasoconstriction, leading to colder extremities.
* Larger body surface area to mass ratio, potentially increasing heat loss.
* Less muscle mass, resulting in lower metabolic heat production.
* Higher body fat percentage, which provides insulation and may improve tolerance to cold water swims

61
Q

List some practical considerations for exercising in the cold.

A
  • Dress in layers, using materials with wicking properties for the first layer.
  • Protect extremities (toes, fingers, nose, and ears) from wind chill.
  • When jogging outdoors, run into the wind during the first half of the workout.
  • Adjust headwear and gloves based on conditions to regulate heat loss.
  • Pay attention to winter race climate guidelines
62
Q

How much heat is lost through the head and neck area during exercise in the cold?

A

Up to 20-30% of heat loss can occur through the head and neck, depending on temperature and wind conditions

63
Q

Is it possible to freeze your lungs?

A

It is highly unlikely to freeze your lungs during exercise, even in extremely cold temperatures. The conducting zone of the respiratory system is very efficient at warming and humidifying inhaled air. [29] For example, dogs have exercised at -100°C without adverse effects because inhaled air is warmed to 18°C by the time it reaches the lower trachea

Kin 200 (7 decks)

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