temperature regulation

normal core temperature

37 C°

core temp above 45°c can lead to...

cellular damage and enzymes

lead to death

core temp below 34°c can lead to...

decreased metabolism and cardiac arrhythmias

thermal homeostasis

balance in heat gain and heat loss

what percent of energy expenditure is released as heat during exercise

70-80%

what are involuntary productions of heat

shivering and actions of hormones (non-shivering thermogenesis)

at rest, what is the body's primary way of losing heat

radiation (60%) - heat transfer via infrared rays

____ is body heat loss due to contact with another surface

Conduction

____ is heat transferred from body to air or water

Convection

what effect can higher relative humidity and temperature have on evaporative capacity

lowers evaporative capacity ~ reduces ability to lose body heat during exercise

what is the key means of heat loss during exercise

evaporation

where is heat that is produced and not lost stored in the body

stored in the body tissues to increase body temperature

Preoptic-anterior hypothalamus (POAH)

operates much like a thermostat to maintain a relatively constant core temperature around a "set point"

what is the POAH response to increase in core temp

stimulation of sweat glands (evaporation) and cutaneous vasodilation (increased heat loss)

what is the POAH response to decrease in core temp

shivering and norepinephrine release (increase heat production) and decrease skin blood flow (vasoconstriction)

fever

results from an upward shift of hypothalamic set point due to pyrogens

which load exercise (arm vs leg) lead to more heat production

leg due to more muscle mass contraction

heat index

measurement of how hot the the body "feels"

High relative humidity and high ambient temperature lowers ____ and increases ___

Body heat loss, body temperature

what control are sweat glands and sweat production under

sympathetic cholinergic control

what three types of sweat glands contribute to cooling

apocrine

apoeccrine

eccrine

____ is open to hair follicles, limiting effectiveness

Apocrine

____ is located in few body regions, limiting effectiveness

Apoeccrine

which sweat gland is most abundant and most responsible for heat loss

eccrine

how much loss in body weight due to dehydration can impair exercise performance

1-2% body weight loss

guidelines for hydration

400-800 mL fluid prior to event

150-300 mL fluid every 15-20 min

consume 150% of weight loss for rehydration

why is endurance exercise performance impaired in hot/humid environments

- accelerated muscle fatigue (increase radical production, decreased muscle pH, muscle glycogen depletion)

- cardiovascular dysfunction (reduced SV, CO during high intensity, and muscle blood flow)

- central nervous system dysfunction (motivation/voluntary activation of motor units)

is there a gender difference in thermoregulation

no

does age impair thermoregulation capacity during exercise in heat

yes, skin blood flow is reduced in older individuals

acclimation

rapid adaption to environment (days to weeks)

acclimatization

long time adaptation (weeks to months)

acclimation loss due to inactivity (by day)

significant decline in 7 days

complete loss in 28 days

what adaptations take place during heat acclimation

increased plasma volume

earlier onset of sweating

reduced NaCl loss in sweat

reduced skin blood flow

increased cellular heat shock proteins (prevent cellular damage)

what are the first initial changes that take place in acclimation... what are the longest changes

changes in HR and plasma volume... changes in sweat rate

cold stress and performance

cold can reduce blood flow and rate of neural transmission (mostly to hand) which results in loss in dexterity and motor skills

acclimation in cold environments

- results in lower skin temperature at which shivering begins

• increased non-shivering thermogenesis.

- improved ability to maintain a higher hand and foot temperature during cold

• improved peripheral blood flow

- improved ability to sleep in the cold

• due to reduced shivering

- cold adaptations occur rapidly (within first 7 days of chronic cold exposure)