Chapter 12 & 23 Flashcards
humans are
homeotherms
*maintain constant body core temperature through metabolic heat production
*heat loss must match heat gain so that we avoid increases in body temperature
normal core temperature
37C
temperatures above 45C
can damage proteins and enzymes can lead to death
temperatures below 34C
can result in decreased metabolism and cardiac arrythmias
thermal gradients
exists between deep body core to skin surface
- typical gradient is 4C
-in extreme cold may be 20C
what measures deep body (core) temperature
ingestible temperature pill
what measures skin (shell) temperature
thermistors at various locations and can calculate mean skin temperature
voluntary heat production
exercise
70-80% EE released as heat (metabolism) dependent on efficiency
involuntary heat production
shivering - increases heat production by ~5x
non-shivering thermogenesis - in brown adipose tissue (mediated by thyroxine and catecholamines)
mechanisms of heat loss/transfer
evaporation
radiation
conduction
convection
evaporation
primary mechanism in hot environments
body heat causes sweating which is lost from the body surface when changed from a liquid to a vapor
radiation
body heat loss to nearby objects without physically touching them
convection
body heat is lost to convection which becomes warmer, rises and is replaced with cooler air
conduction
body heat is lost to nearby objets through direct physical touch
evaporation rate depends on
temperature and relative humidity
convective currents around the body (fan vs no fan)
amount of skin surface exposed
high relative humidity decreases the vapor pressure gradient between the skin and the environment leading to
less evaporation
- the warmer = increased vapor pressure = less evaporation
- the more humid = increased water molecules in the air = decreased evaporation
heat index
measurement of body’s perception of how hot it feels
high relative humidity does what to evaporative heat loss
decreases it and increases the perception of how hot it feels
POAH (preoptic anterior hypothalamus)
body’s thermostat
* responds to increased core temperature
increased core body temperature causes
the POAH to stimulate the sweat glands for evaporative heat loss as well as cutaneous vasodilation to the periphery
how does the POAH stimulate sweat glands and cutaneous vasodilation
via sympathetic cholinergic control of sweat glands and cutaneous vasculature
stimulation of sweating mechanism
in eccrine sweat glands, stimulation occurs via activation by ACh, which binds to mACHR
ACh binding to mACHR causes vasodilation of blood vessels in the skin
as exercise intensity increases, what thermal events occur
heat production increases due to muscular contraction (metabolism)
linear increase in body temperature (core body temperature increases proportional to active muscle mass)
what determines heat production during steady state exercise
EXERCISE INTENSITY
NOT environmental temperature
different work rates = different heat production