Chapter 25 - Thermoregulation Flashcards
What is the average core temperature?
36-37.8C
How much does metabolism rise in elite athletes during intense aerobic exercise?
- 20-25 above resting levels
What does the increase in metabolism during intense exercise do regarding thermoregulation?
- increases core temperature
- Most of metabolisms results in heat production
What is the O2 consumption at rest?
0.25L/min
What is the O2 consumption during maximal exercise?
5L/min
How does heat loss occur in the body?
- Radiation
- Conduction
- Convection
- Evaporation
How is heat gained in the body?
- Basal Metabolic Rate
- Muscular Activity
- Hormones
- Thermic Effect of Food
- Postural Changes
- Environment
What does conduction heat exchange involve?
- Direct heat transfer from one molecule to another through a liquid, solid, or gas
How does conduction contribute to a small amount of heat loss in the body?
- Directly through deep tissues to cooler surface
What does the rate conductive heat loss depend on?
- Temperature gradient between the skin and surrounding temperature
- Thermal qualities of the surface
What does convection heat exchange involve?
- Transferring heat by motion of gas or liquid across a heated surface
How does heat loss occur with convection?
- Air moves around us, passes over the skin, heat is exchanged with the air molecules.
What contributes to the rate of heat exchange by convection?
The greater the movement, the greater the rate
What do all objects continually emit?
- Electromagnetic heat waves or radiant energy
What are the primary methods for eliminating body heat during rest?
- Radiation and Convection
Describe Radiation
- Emission of electromagnetic heat waves or radiant energy
What is the primary avenue for heat dissipation during exercise?
- Evaporation
What happens when a fluid evaporates and turns into a gaseous form?
- Heat is lost (because its required)
What three factors influence the total amount of sweat vaporized from the skin and pulmonary surfaces?
- Surface exposure to the environment
- Temperature and relative humidity of the ambient air
- Convection air currents about the body
How does the body gain heat from radiation?
- Sky
- Solar
- Ground
How does the body lose heat from radiation?
- From the body
How does the body lose heat through evaporation?
- Respiratory
- Sweat
How does the body lose heat through convection?
- Muscle blood flow convection
- Skin/Blood convection
How does the body lose heat through conduction?
- Skin to surrounding area
What range of body temperature change can the human body tolerate?
- Decline of 10C
- Increase of 5C
What plays a primary role in the balance of body temperature?
- Hypothalamus
What provides input to the central control center for temperature regulations?
- Thermal receptors in the skin
What is the water vapor pressure gradient?
- Difference between water vapor pressure on skin and in air
What is the heat produced in muscles an example of?
- Conduction
What is the heat transported in the blood and example of?
- Convection
Where are the central receptors located?
- Hypothalamus
- Other brain regions
- Spinal Cord
What are central receptors sensitive to?
- Blood temperature changes as small as 0.01C
What triggers the hypothalamus reflexes that conserve or eliminate body heat?
- Very small changes in temperature changes of the blood passing through the hypothalamus
What happens at rest in the heat, regarding heat regulation?
- Increase HR and Cardiac Output
- Superficial and Venous Blood vessels dilate
- Warm blood diverted to skin
What are the two competitive cardiovascular demands during exercise in heat?
- Muscles require oxygen to sustain energy metabolism
- Arterial blood that diverts to the periphery to cool the body cannot deliver its oxygen to active muscle
What happens to cardiac output during extreme heat stress?
- 15-25% passes through the skin
What happens to stroke volume and heart rate at submaximal exercise in heat?
- Lower Stroke Volume
- Higher Heart Rate
What happens to cardiac output during submaximal exercise in heat?
Maximal Decrease
- Rise in HR does not offset drop in stroke volume
What circulatory adjustments during exercise in heat lead to increased blood lactate accumulation?
- Decreased lactate uptake by the liver from reduced hepatic blood flow
- Less muscle catabolism of circulating lactate because heat dissipation diverts cardiac output to the periphery
What does sweat do for hydration and electrolyte saturation in the body?
- Reduces both
What does a single bout of activity in heat do to aldosterone?
- Stimulates its release
What does aldosterone do?
- act on renal tubules
- Increase sodium reabosorption
What is aldosterone?
- Sodium-conserving hormone
What is vasopressin?
- Antiduretic hormone
What does exercise in heat do to vasopressin?
- stimulates release
Where is vasopressin released from?
- Hypothalamus
What does vasopressin do?
- Increases permeability of collecting tubules of kidneys
- facilitate fluid retention
Describe the pathway of fluid loss and retention during exercise
- Muscular activity promotes sweating which causes loss of blood plasma, resulting in hemoconcentration and increased blood osmolality.
- Increased blood osmolarity stimulates osmoreceptors in the hypothalamus which sends a neural signal to the posterior pituitary gland.
- The posterior pituitary gland secretes ADH into blood which acts on the kidneys, increasing water permeability of the renal tubules and collecting ducts.
- Leads to increased reabsorption of water and decreased urine output aids in minimizing body fluid loss.
How much sweat does moderate exercise for an hour produce?
- 0.5-1L sweat loss
What places a demand on fluid reserves? what can it lead to?
Evaporative Cooling
- Lead to dehydration
What are the 5 factors that coincide with fluid loss?
- Lower plasma volume
- Depressed skin blood flow for a given core temperature
- Reduced Stroke Volume
- Increased Heart Rate
- General Deterioration in Circulatory and Thermoregulatory efficiency in exercise
What does ingesting fluid during exercise do?
- Increases blood flow to the skin for effective cooling
What does fluid replacement during exercise need to focus on?
- Maintaining plasma volume
- Optimal circulation and sweating
What provides the most effective defense against heat stress?
- Adequate hydration
What is hyperhydration?
- Ingesting extra water
Why might hyperhydration be beneficial before exercise in heat?
- Offers thermoregulatory protection
What are 3 practical ways to promote acute pre-exercise hyperhydration?
- Consume 500mL H2O before sleeping
- Consume 500mL upon awakening
- Consume 500mL of cold water 20 min before exercise
What do changes in body weight following exercise indicate?
- Water loss
- Adequacy of rehydration
What are ideal conditions for rehydration?
- Intake matches outtake
- Water intake equal rate to loss through sweat
What does each pound of weight lost represent?
- 450mL dehydration
How can you recover electrolytes lost during exercise through sweat?
- Add them to rehydration drink
What does the american college of sport medicine recommend for consuming sports drinks?
- 0.5-0.7g Na/L of fluid during exercise
What is urine volume inversely related to?
- Beverage’s sodium content
What does a modest rise in core temperature during exercise represent?
- Favourable adjustment that optimizes physiologic and metabolic functions
What 5 factors interact to improve physiologic adjustment and exercise tolerance during environmental heat stress?
- Acclimatization
- Training Status
- Age
- Gender
- Body Fat Level
What does repeated exposure to hot environments when combined with physical activity do?
- Improves exercise capacity with less discomfort upon subsequent heat exposure
What does the term heat acclimatization describe?
- Collective physiologic adaptations that improve heat tolerance
When does a major portion of heat acclimatization occur?
- First week of heat exposure
What are the heat acclimatization responses? (8)
- Improve Cutaneous Blood Flow
- Effective distribution of Cardiac Output
- Lowered Threshold for start of sweating
- More effective distribution of sweat over skin surface
- Increased sweat output
- Lower salt concentration of sweat
- Lower skin and core temp and HR for standard exercise
- Less reliance on carbs during exercise
What is the effect of the heat acclimatization response: improved cutaneous blood flow?
- Transports metabolic heat from deep tissue (core) to shell
What is the effect of the heat acclimatization response: Effective distribution of cardiac output?
- Appropriate ciruclation to skin and muscles to meet demand of metabolism and thermoregulation
- Greater blood pressure stability during exercise
What is the effect of the heat acclimatization response: Lowered Threshold for start of sweating?
- Evaporative cooling begins early in exercise
What is the effect of the heat acclimatization response: More effective distribution of sweat over skin surface?
- Optimum use of effective body surface for evaporative cooling
What is the effect of the heat acclimatization response: Increased sweat output?
- Maximizes evaporative cooling
What is the effect of the heat acclimatization response: Lower salt concentration of sweat?
- Dilute sweat preserves electrolytes in extracellular fluid
What is the effect of the heat acclimatization response: Lower skin and core temperature and heart rate for standard exercise?
- Frees greater proportion of cardiac output to active muscles
What is the effect of the heat acclimatization response: Less reliance on carbohydrate catabolism during exercise?
- Carbohydrate sparing
How do trained individuals living in temperate climates respond to severe heat compared to sedentary counterparts?
- More effectively
What does training do for heat managment?
- Increases sensitivity and capacity of the sweat response
- Sweating begins at a lower temperature
how do trained individuals differ from sedentary individuals regarding cutaneous blood flow?
- Greater cutaneous blood flow at given internal temperature
- Greater cutaneous blood flow at given percentage of VO2max
Are there age-related decrements in thermoregulation for marathon runners?
- NO
Who has more heat-activated sweat glands per unit skin area, children or adults?
- Children
What do children do compared to adults regarding thermoregulation?
- Sweat less
- Maintain higher core temperature
What are the recommendations for children regarding physical activity in high temperatures?
- Intensity of effort decreased
- Longer duration for acclimatization
Who sweats more, men or women?
- Men
What do women typically have that helps them with thermoregulation? How?
Smaller, relatively larger body surface area per unit mass
- Favours greater heat dissipation through circulatory mechanisms
What does excess body fat represent regarding thermoregulation?
- Liability when exercising in heat
How does increased fat mass reduce the capacity for thermoregulation?
- Higher specific heat capacity
- Acts as insulator
- Limits heat conduction to the periphery
How do larger people have a limited effectiveness of sweat evaporation?
- Smaller surface area to body mass ratio
What are Heat Cramps?
- Severe involuntary, sustained, and spreading muscle spasms
When do Heat Cramps occur?
- During or after intense physical activity, usually in exercised muscles
When does heat exhaustion occur?
- ineffective circulatory adjustments compounded by depletion of extracellular fluid, principally plasma volume from excessive sweating
What is the most complex problem from heat exposure?
- Heat Stroke
What does Heat Stroke Reflect?
- Failure of heat-regulating mechanisms from an excessively high core temperature
What are some warning signs of Heat-related Disorders?
- Nausea
- Chills, Goose Bumps
- Headaches
- Fatigue
- Excessive Thirst
- Cessation of Sweating
- Profuse Sweating
- Confusion
- Painful Large Muscle Cramps
- Loss of Consciousness
Is Oral temperature reliable for testing core temperature?
- NO
What does the hypothalamus sense regarding thermoregulation?
- Increased Temperature
Where does the hypothalamus send signals when it senses an increase in temperature?
- Sweat glands become active
- Vasodilation in skin blood vessels
How does the hypothalamus activating the sweat glands help with thermoregulation?
- Increase evaporative heat loss
How does the hypothalamus vasodilating skin blood vessels help with thermoregulation?
- More Heat lost from the skin
What vascular adjustments occur in response to cold?
- Cutaneous cold receptors constrict peripheral blood vessels
How does the cutaneous cold receptors constricting peripheral blood vessels in the cold help?
- Reduce flow of warm blood to the body’s surface
- Redirecting warm blood to core
What is the greatest contribution to defending against the cold?
- Physical Activity
Exercise energy metabolism can sustain constant core temperature in the cold up to what air temperature?
-30C
What does shivering in the cold do?
- Generates metabolic heat
Describe Shivering
- Rapid, involuntary cycle of contraction and relaxation of skeletal muscle
How much can shivering increase the body’s heat production by?
- four to five times
What neurotransmitters increase the heat production during cold exposure?
- Epinephrine
- Norepinephrine
What does cold stress stimulate from the thyroid?
- Release of Thyroxine
What does the release of thyroxine from the thyroid during cold stress do?
- Increases resting metabolism
What is normothermia?
98.6F
What temperature range is mild hypothermia?
95-91.4F
What changes might occur during mild hypothermia?
- Max Shivering
- Increased Blood Pressure
- Amnesia
- Dysarthria
- Poor Judgement
- Behaviour Change
- Ataxia
- Apathy
What temperature range signifies moderate hypothermia?
89-85F
What changes might occur during moderate hypothermia?
- Stupor
- Shivering Ceases
- Pupils Dilate
- Cardiac Arrhythmias
- Decreased Cardiac Output
- Unconsciousness
What temperature range signifies severe hypothermia?
82-56F
What changes might be seen in severe hypothermia?
- Ventricular fibrillation likely
- Hypoventilation
- Loss of reflexes and voluntary motion
- Acid-base disturbances
- No Response to pain
- Reduced cerebral blood flow
- Hypotension
- Bradycardia
- Pulmonary Edema
- No Corneal Reflexes
- Areflexia
- Electroencephalographic Silence
- Asystole
- Lowest Infant Survival
- Lowest Adult Survival
How does the hypothalamus help in thermoregulation during cold temperatures?
- Senses drop in blood temperature
- Sends signal to skin blood vessels for vasoconstriction
- Sends signals to skeletal muscles for shivering
Does cold ambient air pose special danger to the respiratory passages?
- NO
What happens when extremely cold ambient air enters the respiratory tract?
- Reaches 26-32C before it reaches the bronchi
What evidence contradicts the theory that cold ambient air poses no threat to damaging the respiratory passages?
- Athletes who exercise in very cold environments have a higher occurrence of hyper-reactivity or asthma compared to those who exercise in warmer environments
What did the study on Alaskan sled dogs support?
- Strenuous exercise in cold environments can lead to lower airway disease
What did the study on airway remodeling from cold-weather exercise in elite athletes find?
- Prolonged repeated exposure of the airways to inadequately conditioned air may induce inflammation and remodeling in competitive skiers
