Chapter 12/23: Temperature Regulation & Altitude Flashcards
describe the term homeotherms
maintain constant body temperature, heat loss must match heat gain
normal core temp
37 degrees celsius
temperatures above 45 degrees celsius might
damage proteins and enzymes, leading to death
temperatures below 34 degrees celsius might
result in decreased metabolism and cardiac arrhythmias
describe the thermal gradient. typical value?
thermal gradient between deep body core temp and skin surface (typically 4 degrees celsius but can be up to 20 degrees celsius in extreme cold)
how is deep body (core) temp measured?
measured at rectum, ear or esophagus (in the lab) or ingestible pill (athletes can use during practice sessions)
how is skin (shell) temperature measured?
using thermistors at various skin locations, calculate the mean skin temp
3 methods of heat production (both voluntary and involuntary)
exercise (voluntary): 70-80% of energy expenditure released as heat
shivering & non-shivering thermogenesis (involuntary)
hormones that cause non-shivering thermogenesis
thyroxine (thyroid hormone) and catecholamines
4 mechanisms of heat loss
1) evaporation: via sweat
2) radiation: body heat lost to nearby objects
3) conduction: body heat lost by physically touching something (ice cubes)
4) convection: movement of air molecules (fan)
3 factors influencing evaporation rate
1) temperature and relative humidity
2) convective currents around the body
3) amount of skin surface exposed
how does high relative humidity affect evaporation rate?
high relative humidity decrease the vapor pressure gradient between the skin and the environment, which leads to decreased rate of evaporation
what is the heat index? how does high relative humidity affect the heat index?
the heat index is a measure of the body’s perception of how hot it feels (high relative humidity reduces evaporative heat loss which leads to increased perception of how hot it feels)
how does the body respond to increased core temperature?
the preoptic anterior hypothalamus stimulates sweat glands (evaporative heat loss) and cutaneous vasodilation via sympathetic cholinergic control of sweat glands and cutaneous vasculature
what ligand and receptor are responsible for stimulating sweat in eccrine glands?
Ach binds to mAchR
what ligand and receptor are responsible for vasodilation of blood vessels in the skin?
Ach on mAchR
what happens to heat production as exercise intensity increases?
heat production increases due to muscular contraction, there is a linear increase in body temp
core temp increase is proportional to:
active muscle mass
what determines heat production during steady state exercise? what is not responsible?
exercise intensity, not environmental temperature
submaximal exercise in a hot/humid environment leads to:
higher core temperature, which leads to risk of hyperthermia and heat injury
what happens to oxygen uptake during prolonged exercise in a hot and humid environment?
upward drift in oxygen uptake (VO2)
how is cardiac output affected during exercise in hot and humid environments?
to compensate for the decrease in stroke volume, heart rate gradually creeps up to maintain cardiac output
how is blood flow affected during exercise in hot and humid conditions?
blood flow is shunted away from working muscle and nonessential areas (gut, liver, and kidneys) to the skin
how does exercise in hot humid environments affect sweat rate?
higher sweat rate, up to 4-5 L / hour