Exam 3 Flashcards
Efficiency of human body to perform physical work
≈15-30% (slightly higher @ rest ≈34%)
Remaining 70-85% of expended energy converted to…?
heat
Typical resting core temp.
≈ 37 degrees C (98.6 degrees F)
Humans either retain or dissipate heat based upon…?
how close core temp. is to your typical resting level
The neuro-endrocrine organ responsible for maintaining core temp. as close to 37 C as possible
Hypothalamus
Temp. regulation centers collectively function as a bi-directional thermostat & are situated on:
hyperthermia: anterior aspect of hypothalamus
hypothermia: posterior aspect of hypothalamus
Other functions of hypothalamus:
water balance
sugar & fat catabolism
satiety (hunger) center
controls other endocrine glands
When the core temp. ___________ is interrupted, the temp. center w/in hypothalamus activates several mechanisms which attempt to return the core temp. to normal
homeostasis
Core temp. too low, it’s increased by…?
- heat conservation
2. increased heat production
Heat conservation initiated via:
- decreased sweat rate
- decreased blood flow to extremities & to skin’s surface (DERMAL VASOCONSTRICTION)
Heat production initiated via:
- SHIVERING
(SNS increases catabolic rate 2-4 times resting level) - hypothalamus may trigger THYROID GLAND TO RELEASE THYROXIN which increases catabolic rate
- hypothalamus may trigger ADRENAL MEDULLA TO RELEASE CATECHOLAMINES (EPINEPHRINE & NOREPINEPHRINE) which also increase catabolic rate
When core temp is too high, it’s decreased by…?
- Heat dissipation
2. Decreased heat production (possible in resting state)
Heat dissipation initiated via 2 precursors:
- Increased sweat rate
- Increased blood flow to extremities & skin surface (DERMAL VASODILATION)
After one or both precursors have been initiated, one or more of the following processes may contribute to the dissipation of excess heat via:
- Conduction
- Convection
- Radiation
- Evaporation
After dermal vasodilation: CONDUCTION
Transfer of heat energy via DIRECT SURFACE CONTACT from hotter to cooler surface
-absorption vs. dissipation
Temperature gradient
transfer of heat energy from hotter to cooler surface temperature
After dermal vasodilation:
CONVECTION
subsequent to transfer of heat to a gas or liquid, the heated substance rises (temperature gradient) — gas Vs. liquid - absorption Vs. dissipation
After dermal vasodilation: RADIATION
transfer of heat via electromagnetic waves
(temperature gradient required) - absorption Vs. dissipation
After increased sweat rate:
EVAPORATION
- each gram of vaporized water dissipates ~ .58 kcal of heat energy
- called the energy of vaporization OR heat of vaporization
Do dermal vasodilation & perspiration dissipate heat?
Dermal vasodilation & perspiration do NOT dissipate heat, but one or both are necessary precursors to heat loss.
Consider these for temperature regulation:
- artificial environments (clothes, rooms)
- effects of ethyl alcohol
hot vs. cold considerations
Effects of ethyl alcohol:
- dermal vasodilation
- diuretic
- depressant
Decreased heat production initiated via:
-Decreased metabolic rate: slowing down or ceasing some physiological functions
(obviously, a person would have to stop exercising in this case)
Do anatomic &/or physiological differences between males and females make a difference in the responses to hot/humid ambient conditions?
Yes; but they are not understood
Who has more sweat glands; males or females?
Females;
Regardless, females sweat less than males (generally speaking) likely as a result of gender differences in selected hormone levels
Who has more body fat; males or females?
Females typically have ~ 10% more body fat:
- much distributed in the subcutaneous region
- fat serves as an insulator
- greater amounts of subcutaneous fat result in less angular surface area, so less surface area/unit of body mass exists
Who has lower VO2 max; males or females?
- females frequently have lower VO2 max when expressed in absolute or relative terms
- the lower the VO2 max , the lower the efficiency of heat-dissipation mechanisms
Males/females typically respond to elevated core temps. w/ greater dermal vasodilation?
Females
Generally speaking about dissipating heat, which gender relies mainly on EVAPORATION, CONDUCTION, RADIATION, & CONVECTION?
- MEN RELY ON EVAPORATION more than females do
- FEMALES RELY ON CONDUCTION, CONVECTION, & RADIATION more than males do
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 proportionally lowers the quantity of blood available to ____ ____ during ___?
The elevated sweat rate in males reduces overall blood volume resulting in a similar net effect unless fluids are restored in a timely manner.
SKELETAL MUSCLES during EXERCISE
Males tend to have an advantage in ___, ___ ambient conditions
hot, dry
Females tend to have an advantage in ___, ___ ambient conditions
warm, humid
Dehydration/hypohydration is a condition in which…?
body fluids have been excessively lost via sweating, respiration, blood loss, &/or urinary/GI excretion
Dehydration results in an increase in plasma ___ & ___ concentrations due to a substantial loss of plasma water.
protein & electrolyte
A decrease in total blood vol. results in a decreased ___ ___?
stroke volume (SV)
In order to maintain cardiac output (Q) during submaximal exercise, heart rate (HR) must be ___ when compared to a euhydrated state?
increased
Dehydration also results in a ___ maximal cardiac output?
decreased
Q= HR x SV
- The potential for heat dissipation via conduction, convection, and radiation is reduced by a decrease in total blood volume which results in decreased ___ ___ ___?
- Which also results in an ___ core temp?
- Peripheral blood flow
2. elevated
What percentage of a decrease in body weight via dehydration will reduce physical work capacity & local muscular endurance?
5%
Is strength affected by dehydration?
not really, except extreme cases
1 lb of body weight from fluid losses = ? (how much water)
a pint
Is thirst a good indicator of fluid needs during exercise?
no
Heat acclimatization is characterized by individuals
- sweating at lower core temps.
- sweating more at all elevated core temps.
- hypotonic sweat
Heat acclimated people will:
- store less heat during the initial phases of exercise
- will reach a lower thermal steady state
Less dermal blood flow and the availability of more cardiac output for active tissues is caused by ____ ___ ___ ___ ____?
cooler core and skin temps.
If cooler core and skin temps are due to sweat loss, blood volume decreases which means ____ ____ _____.
less cardiac output
What is albumin?
blood borne protein
most abundant protein found in blood
During heat acclimatization, degradation of _____ is reduced & production by the liver is at least maintained.
albumin
This results in an ______ in the amount of albumin that is circulating.
increase
Albumin binds with fluid.
Each gram of albumin binds with how much blood plasma?
13 ml
Albumin binds with ___ ___ ___s and various hormones.
free fatty acids (FFA)
A fully heat acclimated person will have retained about ____% more plasma than the non-acclimated person because of _____ albumin levels.
20%
increased
- B/c a greater fluid reserve exists for sweating and the maintenance of SV and Q
This blood adaptation is normally completed within ___ weeks.
2
A well-trained individual may be about ___% heat acclimated even when conditioning occurs in a cool environment.
about 50%
adaptation takes about 1 week
Training activities typically result in ___ core temps, and in turn, will partially acclimate the person to high thermal conditions.
elevated
Performing activities that mainly involve the ___ system will be compromised when ambient conditions are hot/humid, especially if noticeable heat acclimatization is lacking.
CR system
