Thermal Conditions Test #3 Flashcards
in order to maintain a constant core temperature, what must happen?
heat loss must equal heat gain
thermal gradient is present where?
from body core to skin surface
The efficiency of the human body to perform physical work
around 15-30%
the efficiency of the human body to perform work at rest
around 34%
how much remaining energy is converted to heat
70-85%
typical resting core temperature?
37 degrees C
or 98.6 degrees F
this can vary within individuals
humans either _____ or ______ heat depending on how close core temperature is to your typical resting level
they either retain or dissipate heat
the hypothalamus is what kind or organ?
neuro endocrine organ
what is the hypothalamus responsible for?
maintaining core temperature as close to 37 degrees C as possible
the hypothalamus has many functions but ____ is especially important
temperature control
temperature regulation centers function as what
bi-directional thermostat
temp. regulation centers situated (built upon) what?
1- anterior aspect of the hypothalamus for hyperthermia
2-posterior aspect of the hypothalamus for hypothermia
when body temperature rises well above normal
hyperthermia
when body temperature is dangerously below normal
hypothermia
Other functions of the hypothalamus:
- water balance
- sugar and fat catabolism
- satiety (hunger) center
- controls other endocrine glands
When core temp. _____ is interrupted, temp. centers within the _____ activate several _____ that attempt to return core temp. to normal
homeostasis
hypothalamus
mechanisms
when core temperature is too low, core temp is increased by:
- heat conservation
- increased heat production
heat conservation is initiated via:
- decreased sweat rate
- dermal vasoconstriction
a decreased blood flow to extremities and skin
dermal vasoconstriction
increased heat production is initiated via:
- shivering-sns increases catabolic rate 2-4x more than resting
- hypothalamus may trigger the thyroid gland to release thyroxin, which also increases catabolic rate
- hypothalamus may trigger adrenal medulla to release catecholamine’s, which also increase catabolic rate
catecholamine’s are also known as
epinephrine and norepinephrine
when core temp. is too high, core temp. is decreased via:
- heat dissipation
- decreased heat production (possible at resting state)
heat dissipation initiation via 2 precursors:
1- increased sweat rate
2- dermal vasodilation
increased blood flow to extremities and skin surface
dermal vasodilation
subsequent to dermal vasodilation, what can happen?
- conduction
- convection
- radiation
the transfer of heat energy via direct contact from hotter to cooler surface
- conduction
- involves temp. gradient
- absorption vs. dissipation
after(subsequent) the transfer of heat to a gas or liquid, the heated substance will rise
- convection
- temp. gradient
- gas vs. liquid
- absorption vs. dissipation
transfer of heat via electromagnetic waves
- radiation
- requires temp. gradient
- absorption vs. dissipation
After increased sweat rate, what can happen?
evaporation
each gram of water dissipates around .58kcal of heat energy
-evaporation
1g H2O= .58kcal heat energy
- energy or vaporation
- heat of vaporation
Do dermal vasodilatation and perspiration dissipate heat?
NO! However, one or both are necessary precursors for heat loss
Consider these for temp. regulators:
- artificial environment (clothing, room, chamber)
- effects of ethyl alcohol (dermal vasodilation, diuretic, depressant)
- Hot vs. Cold considerations
Decreased heat production initiated by:
- decrease metabolic rate (slowing down or ceasing of come physiological functions)
* a person would obviously have to stop exercising in this case
Do anatomic and/or physiologic difference exist between males and females?
yes, but the mechanisms associated with the different reactions to hot/humid conditions are not completely understood
who has more sweat glands?
females, they sweat less bc is it likely a result of gender differences in selected hormone levels
who has more body fat/ how much?
females, 10%-much in the subcutaneous layer.
Fat serves as a what
insulator
Greater amounts of subcutaneous fat will result in what?
less angular surface area, so less surface area/ unit of body mass exist
Who has lower maximal O2 uptake?
-females- have lower VO2Max when expressed in absolute or relative terms
the lower the VO2 max…..
the lower the efficiency of heat-dissipation mechanisms
females typically respond to elevated core temps with _____ vasodilation than do males
greater
men rely on _____ to dissipate heat, greater than women; women rely on _______ to dissipate heat more than men
- evaporation- men
- conduction, convection, radiation-women
Well-conditioned individuals will be at least partially heat acclimated & so will sweat sooner in response to high core temps. as well as sweat more at any point in time: T or F?
True
Do conditioning levels contribute to a person’s ability to respond to heat stress?
yes
dermal vasodilation proportionately lowers the quantity of _____ available to skeletal muscles during ______
blood, exercise
the elevated sweat rate in males reduces ___________, resulting in a lower quantity of blood unless _________
- overall blood volume
- fluids are restored in a timely manner
each sex may have an advantage to dissipate heat when?
under certain specific environmental conditions (especially when VO2max levels are matched)
_____ tend to have an advantage in hot, dry ambient conditions
males
_______ tend to have an advantage in warm, humid ambient conditions
females
dehydration is also known as
hypo hydration
dehydration (hypohydration) occurs because of what??
an excessive loss in body fluids via: sweat, respiration, blood loss, urinary or GI execretion
dehydration (hypohydration) results in what?
an increase in plasma protein and electrolyte concentrations due to a substantial loss of plasma water
a ______ in total blood volume results in a decrease stroke volume
decrease
in order to maintain Q during SUBMAXIMAL exercise, HR must ______ when compared to a euhydrated state
increase
euhydration
normal state of body water content
dehydration will also result in a ______ maximal cardiac output
decreased
> > Q= HR x SV
decreased cardiac output = heart rate x stroke volume
this is a result of dehydration
a _____ in total blood volume will result in decreased peripheral blood flow.
this _____ the potential for heat dissipation via ____, ______, _____.
this also results in an ______ core temp.
decrease
decreases or reduces
convection, conduction, radiation
elevated
a 5% _____ in body weight via dehydration reduces what?
decrease
physical work capacity and local muscular endurance
except in extreme cases, strength is minimally affected by what?
dehydration
thirst is usually an _____ indicator of fluid needs and generally does not keep up with water deficits during exercise
inadequate
for every 1 lb of body weight from fluid losses around ____
1 pint of water
performance of activities greatly involving the CR system will be compromised when ambient conditions are ____ or _____, especially is large heat acclimatization is lacking
hot or humid
heat acclimatization is characterized by individuals:
- sweating a lower core temps
- sweating more at elevated core temps
- hypotonic sweat
a heat acclimated person will:
- store less heat during the initial phases of exercise
- will reach a lower thermal steady state
