W6 - Thermoregulatory System Flashcards
Contributing factors to heat loss
Radiation
Conduction
Convection
Evaporation
How does heat conservation happen?
When blood is quickly shunted to the deep cranial, thoracic + abdominal cavities.
Contributing factors to heat gain
BMR
Muscular activity
Hormones
Thermic effect of food
Postural changes
Environment
During heat conservation, why is blood rapidly shunted to the deep cranial, thoracic + abdominal cavities?
To optimise insulation from subcutaneous fat + other components of the bodys shell.
What does an increase in internal heat do to the bodys peripheral vessels?
Dilates them as warm blood flows to the cooler periphery.
What contains the central coordinating centre for temperature regulation?
Hypothalamus
What are the 2 ways in which the bodys heat-regulating mechanisms can be activated?
Thermal receptors in skin
Changes in temp of blood that perfuses the hypothalamus
Where do the thermal receptors in the skin provide input to?
Central coordinating centre in hypothalamus
What plays the primary role in maintaining thermal balance?
The central hypothalamic regulatory centre
What do cells in the anterior portion of the hypothalamus detect and what do they receive?
Slight changes in blood temp
Receive peripheral input.
What is the result of the cells activity in the anterior portion of the hypothalamus being heightened?
In regards to the anterior hypothalamus
Initiates coordinated responses to facilitate heat loss = cooling
What provides as the primary monitoring system to asses body warmth?
Temp of blood that perfuses the hypothalamus.
What are the organism types for thermoregulation?
Homeotherms
Endotherms
Ectotherms
Define homeotherms
Have a constant internal body temp regardless of external stimuli
Define endotherms
Generate heat internally
Maintain high basal heat prod
Define ectotherms
Depend on external heat sources
Temp changes w/ env
What is our core body temp?
36.5-37.5
What is the optimal function for our temp?
36.5-40.0
When can hypothermia be established?
When body temp is <35.0
What is the lowest survivable internal core temp?
~14.4
Effects from hypothermia
Loss of motor skills
Shivering
⬇️ blood circulation
⬇️ skin temp
Confusion/fatigue
Loss of consciousness
When can hyperthermia be established?
When body temp is >38.0
What is the highest survivable internal core temp?
~46.5
At what body temp does damage to cells occur?
42.0 + above
Biggest effects of hyperthermia
Heat exhaustion
Heat stroke
Symptoms of heat exhaustion
Faint/dizzy
Excessive sweating
Cool, clammy skin
Nausea
Rapid,weak pulse
Muscle cramps
Symptoms of heat stroke
Throbbing headache
No sweating
Red, hot, dry skin
Nausea
Rapid, strong pulse
Factors affecting core body temp
Body morphology
Environnent
Skin
Metabolic heat production
What comes under body morphology?
Body mass
Body composition
Factors affecting core body temp
What comes under skin?
SA
Temp
Skin wettedness
Factors affecting core body temp
What comes under environment?
Temp
Humidity
Air velocity
Air density
Clothing properties
Define specific heat capacity
Amount of energy req to raise the temp of a given substance by 1 degree celsius
What are the 2 types of heat production?
Voluntary
Involuntary
What comes under voluntary heat production?
Exercise
What comes under involuntary heat production?
Shivering
Hormones (thyroxine + catecholamines)
How many kJ of heat does 1l of O2 produce?
~20kJ
How can you measure core body temp?
Using thermometer probe
Where can the thermometer probe be used to measure core body temp
Hypothalamus
Oesophagus
Rectum
Intestinal
Oral under tongue
Ear drum
What does measuring skin temp depend on?
Ambient temp
Distance from core
Skin bf
In what ways can we externally gain heat?
Sky thermal radiation
Solar radiation
Ground thermal radiation
What does the thermal gradient state?
Heat transfer is always from higher to lower temps
% heat loss at rest from evaporation
~25
% heat loss during exercise from evaporation
~85
How many kJ of heat comes from 1g of sweat?
2.41
When sweating, what are the sweat glands stimulated by?
Sympathetic nervous system. (SNS)
What factors influence evaporation + how?
Air temp (humidity) = ⬇️ it
Convection currents (winds) = ⬆️ it
Skin exposure = ⬆️ it
How is sweat loss calculated?
Change in mass + fluid intake - urine
What does the sweat rate depend on?
Body size
Absolute VO2
Aerobic fitness
Heat acclimatisation
Env
Define radiation
Transfer of heat in form of electromagnetic waves
% of heat loss at rest at room temp from radiation
~60
Define conduction
Heat transfer from body to object w direct contact
% of heat loss at rest at room temp from conduction
~3
Define convection
Heat transfer from 1 place to another by movement of fluids (air/H20)
% of heat loss at rest at room temp from convection
~12
What happens to heat dissipation by convection during exercise?
Reduced
Actions of the hypothalamus following hypothermia
Cutaneous vasoconstriction
Shivering
Catecholamine release
Thyroxin release
Areas of body w. greater heat loss
Skull
Groin
Armpits
Extremities
What does hyperthermia do to sprint + power performance?
Improves it
How does hyperthermia improve sprint + power performance?
⬇️ resistance of muscles/joints
Faster nerve conduction velocity
Improvement in muscle contractile elements
Faster metabolic rate
⬆️ SNS activity
Define Q10 temp coefficient
Measure of rate of change of system as a consequence of increasing temp by 10C.
What does hyperthermia do to endurance performance?
Impairs it
What does hyperthermia do to repeated sprint ability?
Impairs it
Overall why is performance impaired by ⬆️ core temp + sweat rate?
⬇️ plasma vol
⬇️ blood vol
⬇️ venous return
⬇️ end diastolic vol
Cognitive consequences of core temp ⬆️
Fatigue perception ⬆️
Impairment in:
Scanning vigilance
Reaction time
Attention
Visual motor tracking
Order of warning signs for hyperthermia
Heat cramps –> Heat Exhaustion –> Heatstroke
Treatment to heat exhaustion
Cooler env
Elevate feet
Saline (orally or intravenous)
Treatment for heat stroke
Cold water
Ice bath
Wet towels
Methods to reduce hyperthermia during exercise
Heat acclimatisation
Effects of heat acclimatisation
⬇️ body temp at given heat
⬆️ sweat rate + more dilute
⬇️ Skin bf = ⬆️ to muscles
SV maintained
What is the result to the stimulation of cutaneous cold receptors?
Constricts peripheral bv = ⬇️ bf of warm blood to bodys cooler surface + redirects it to warmer core.
What does shivering do?
Generates metabolic heat
Thryoxine
Thyroid hormone that ⬆️ resting metabolism
What 2 competitive CV demands does the body encounter when exercising in the heat?
- Muscles req delivery of arterial blood to sustain energy metabolism
- Arterial blood diverts to periphery to transport metabolic heat for cooling at skin surface (this blood can’t deliver O2 to active muscle)
What effect does ageing have on thermoregulation?
Delays onset of sweating + blunts the magnitude of the sweating response in 1 of 3 ways.
What are the 3 ways in which ageing can blunt the magnitude of the sweating response?
- Modified sensitivity of thermoreceptors
- Limited sweat gland output
- Dehydration-limited sweat output w. insufficient fluid replacement
Functions of the posterior portion of the hypothalamus
⬆️ blood pressure
Shivering or body heat conservation (thermoregulation).
What does damage or destruction to the posterior region of the hypothalamus cause?
Hypothermia
