thermoregulation

what is temperature

a measure of the average kinetic energy of particles in an object

a quantity that expresses how hot something is

what is heat

a form of energy that’s transferred from a higher to lower temp

what does a body core temp of 35 or less mean

hypothermia

what is the usual Tc

36-37 degrees

what is the critical Tc

40-41

what is metabolic heat production

• Only small amount of metabolic energy (around less than 25%) used to support physiological functions

• Thermal energy

what produces metabolic heat

tissues

what leads to an increase in Tc

when heat production is greater than heat loss

what causes a drop in Tc

when heat loss greater than heat production

definition of mechanisms of heat exchange

• When the environment is not thermoneutral, the body uses 4 mechanisms of heat exchange to maintain homeostasis

what are the mechanisms of heat exchange

• Conduction

• Convection

• Radiation

• Evaporation

what component is responsible for heat gain

metabolic heat

what is responsible for heat loss

radiation

conduction

convection

evaporation

what is conduction

direct transfer of heat between molecules

what is convection

heat loss/gain through movement of air/water

how is convection different in water

greater exchange in water (20 x faster)

what is radiation

• transfer of heat with no physical contact, via infrared rays

how does the skin and sun radiate

• sun emits radiant heat

• skin absorbs 97-99% of infrared radiation that strikes it and emits radiant heat

what is evaporation

• heat loss exclusive mechanism

• 25% of heat loss at rest but the most important mechanism during exercise

what are the factors affecting evaporation

• Temperature and relative humidity

• Convective air currents around the body

• Amount of skin surface exposed

what happens in water based exercise

Convection is the main mechanism of heat exchange in water

what controls thermoregulation

hypothalamus

what happens in body when heat is gained

increased blood and internal temp

increased temp is sensed by the hypothalamus

vasodilation occurs so more heat is lost from skin

sweat glands become active which increases evaporative loss

body temp decreases

how does the body respond to heat gain

• Integrated response

• Circulation

  • Peripheral vasodilation, radiative and convective losses increase

• Stimulation of sweat glands

  • Evaporative losses  increase

• Increased depth of respiration

• Hormones

  • Risk of dehydration, aldosterone and vasopressin conserve fluid loss

what happens in the body when lose heat

decreased blood or skin temp

decreased blood temperature sensed by the hypothalamus

vasoconstriction occurs in skin blood vessels to less heat lost to environment

skeletal muscles are activated causing them to shiver which increases metabolism and generates heat

body temp increases

how does the body respond to heat loss

• Integrated response

• Circulation

  • Peripheral vasoconstriction, minimise radiative and convective losses

• Muscle

  • Voluntary - move about

  • Involuntary - shivering

• Hormones

  • Thyroxine, epinephrine - increase metabolism (heat production)

what are the challenges of exercise in heat

• Conflict of interests

  • Need blood to muscles

  • Skin vasodilation - blood to the periphery - reduces blood pressure

  • Need to maintain blood pressure

what is the consequence of exercise in the heat

• Circulatory regulation and muscle blood flow - reduced exercise capacity, can lead to overheating

what happens to performance when dehydrated

In adults reduction in BM is less than 2% = 2% impairment in endurance performance in hot environments

The greater the dehydration, the greater the impact in performance

Anaerobic exercise is less affected by dehydration

mechanism of dehydration beyond fluid loss

Hypothalamus - signals eccrine glands via SNS

Primarily cholinergic innervetion (uses Ach)

Initial filtrate formed from plasma in coil

Electrolyte reabsorption in the duct

Swet secreted from pore at skin surface

what are the types of heat illness

Heat cramps

Heat exhaustion

Heat stroke

what are heat cramps

 

• Involuntary muscle spasms occuring during or after exercising in hot environments

• Core temperature remains in normal range

cause of heat cramps

• Dehydration

• Electrolyte loss

prevention of heat cramps

• Rehydration/ hyperhydration

• Increase electrolyte intake

what is heat exhaustion

A state of overheating caused from prolonged heat exposure and dehydration during or after activity in hot environment

symptoms of heat exhaustion

• Weak rapid pulse

• Low blood pressure, dizziness, general weakness

• Heavy sweating

cause of heat exhaustion

• Ineffective circulatory adjustment (blood pools)

• Excessive sweating (leading to hypovolaemia)

prevention of heat exhaustion

• Stop exercising

• Cool environment

• Intravenous fluid replacement

what is heat stroke

Life-threatening condition where the body overheats and can no longer regulate its temperature during or after exposure to high heat

Requires immediate medical attention

symptoms of heat stroke

• Cessation of sweating

• Hot and dry skin

• Rapid HR and respiration

• Less than 40 degrees

• Loss of consciousness

• Lead to coma/death

• 1 in 3 survivors - permanent damage

 

treatment for heat stroke

• Fluxid replacement

• Alcohol rubs

• Application of ice packs

• Immersion in cold water

how long does heat acclimatisation take

Most changes within 2-3 days, complete by 14

adaptations of heat acclimatisation

• Increased plasma volume

• Earlier onset of sweating and higher sweat rate

• Increased aldosterone

• Cellular production of heat shock proteins

• Reduced skin blood flow

 

what is cold acclimatisation

• Shiver at lower skin temp

• Improved intermittent peripheral vasodilation

• Improved ability to sleep in cold