temp regulation lecture kin

homeotherms

maintain constant body temp; heat loss = heat gain (must)

normal core temp.

37 degrees C

Core temp that destroys proteins and enzymes and lead to death

Above 45 degrees C

Core temp. that may cause slowed metabolism and arrythemias

Below 34 degree C

Thermal gradient

Ideal is around ~4 degrees C

Deep body core temp

measured at rectum, ear, or esophagus

skin temperature

Tskin = (Tforehead + Tchest + Tforearm + Tthigh + Tcalf + Tabdomen + Tback) ÷ 7

Heat production (voluntary)

exercise - 70-80% energy expenditure as heat

Heat production (involuntary)

shivering - increases heat production by ~5x
action of hormones - thyroxine, catecholamines (increase metabolism)

Heat Loss

radiation - transfer of heat via infrared rays; 60% of heat loss

conduction - heat loss due to contact w/ another surface
convection - heat transferred to air or water

Heat loss (evaporation)

-heat from skin converts water (sweat) to water vapor
-evaporation rate depends on - temp and humidity, convective currents, amount of skin surface exposed
-body loses 0.58 kcal heat/ml sweat evaporated
-25% heat loss at rest (most important means of heat loss during exercise)

Total energy expenditure

time spent exercising * VO2 = total energy expenditure

heat storage

-heat produced that is not lost is stored in body tissues
-body heat gain during exercise = (heat produced - heat loss)

amount of heat required to raise body temperature

-specific heat of human body = 0.83 kcal/kg
-heat required to raise body temp 1 C = (specific heat x body mass)

Preoptic Anterior Hypothalamus (POAH)

-like a thermostat; attempts to maintain constant core temperature around a set point
-integration step

response to increase in core temperature (POAH)

stimulation of sweat glands = evaporative heat loss
cutaneous vasodilation = increased heat loss
effectors

response to decrease in core temperature (POAH)

shivering and increase norepinephrine release = increase heat production
decreased skin blood flow via vasoconstriction = decreased heat loss

heat index

measure of body’s perception of how hot it feels
ex) relative humidity added to air temp.
high relative humidity releases evaporative heat loss

exercise in heat

results in reduced ability to lose body heat (higher core temp, risk of hyperthermia and injury)

higher sweat rate (4-5 L/hr, risk of dehydration)

dehydration

dehydration of 1-2% body weight can impair performance

guideline of dehydration

hydrate prior to performance
consume 150-300 ml every 15-20 mins

exercise performance impairment

CNS - decreased motivation, reduced activation of motor units

CV - reduced SV, decreased blood flow

muscle fatigue - decreased muscle pH, muscle glycogen depletion

gender and age differences

small differences in gender heat tolerance
age does not limit ability to thermoregulate

precooling

lowers body temp and improves performance if done before exercise in a hot environment

acclimation

rapid adaptation of environmental change

acclimatization

adaptation over a long period of time

heat acclimation

requires exercise in a hot environment

lost within a few days if inactive (significant decline in 7 days, complete loss after 28 days)

physiological adaptations w/ heat acclimation

10-12% increased plasma volume (BV, SV, and sweating capacity maintained)

reducded skin blood flow

reduced sodium chloride in sweat

higher sweat rate

heat shock proteins

protects cells from thermal injury

stabilizing and refolding damaged proteins