Thermoregulation Learning Objectives (L28) Flashcards
What is the risk of a core temp ~40C
Increase risk of denaturing proteins
What is the core temperature normal range?
Ideal is 37C +/- 1C (36 - 38C)
What is the risk of a core temp ~27C
Increase risk of cardiac arrest
What determines the direction of heat transfer?
Temp gradient
What determines the rate of heat transfer?
- 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)
What brain structure integrates thermoregulation?
Hypothalamus
What are the physiological responses to cold?
Decrease blood flow to skin & extremities
Muscular activity (shivering)
Hormonal secretions (thyroid hormones and adrenaline to raise metabolism)
What are the behavioural responses to cold?
Clothing
Muscular activity (shivering)
Change environment (shelter, warmer)
Consume warm food & drinks
What is the functional adaptation to being able to increase heat generation without shivering called?
Cold acclimatisation
What is the change in observable physiological response for individuals who have acclimated to colder environments? How are they able to do this?
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.
What is the physiological mechanism that would describe the reason to why you take a breath before diving into a pool?
Diving reflex. It has the greatest CV effects when the subject is holding their breath with their face wetted.
What is the diving reflex and why do we need it?
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.
What are the physiological responses to heat?
Increase blood flow to skin & extremities
Sweating
Increase breathing (small effect)
Hormonal secretions
– Decrease thyroid hormones
– Increase fluid balance hormones (ADH and aldosterone)
What are the behavioural responses to heat?
Clothing
Reduce or alter physical activity (swim, shower)
Change environment (shelter, cooler)
Decrease food intake; intake cool drinks
What is the role of the ANS in thermoregulation?
The SNS:
– Vasoconstrict skin vessels in cold
– Vasodilate skin vessels in heat
What division of the ANS mediates sweating
SNS
What temperature is best for performance in longer-duration sports?
Moderately cold
What is the ratio between blood flow to skin and muscle in:
a) hotter environments
b) cooler environments
a) 50/50
b) favours flow to the muscles
Where does does the body prioritise blood flow to the most during exercise: muscle or skin
Muscle
What environmental factor compromises evaporation (cooling)
High humidity
Temperature and what other environmental factor can induce hyperthermia and difficulty regulating fluids?
Humidity
How long does it take to acclimate to heat?
Occur in ~ 1 week of exposure to heat
What are the physiological adaptations in response to heat acclimation
–
– Increased sweat output
–
What is the physiological adaptation in response to exposure to hotter environments that helps in heat conduction and radiation.
Increased blood volume (increased ADH)
Improved skin blood flow (redistribution of blood flow)
Better heat loss
What is the physiological adaptation in response to to exposure to hotter environments that helps prevent excess water loss
Lower threshold for sweating (sweat at LOWER body temp)
Sweat less concentrated (lose less electrolytes)
Better heat loss
How does HR change as heat stress increases
It increases
Higher aerobic fitness levels __________ (improves, reduces) exercise tolerance in heat
Improves
Is sweat more or less concentrated compared to blood?
Less
During humid, hot environments, what are some major considerations for athletes undertaking longer forms of exercise
- 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
By how much (%) should fluid intake exceed fluid loss during exercise in hot, humid environments?
25%
Why do children lose heat quicker compared to adults?
Children have large surface area to body mass
What are the differences in thermoregulatory capacity between males & females
Little difference
What are heat cramps likely due to?
Electrolyte imbalance
What causes heat exhaustion?
Low BP (dilation), weak rapid pulse, headache, dizzy
What are the components and classification of heat stroke?
Elevated core temperature (> 40.5C)
Absence of sweating (dehydration)
