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Ex Phys > Ch 12/23 > Flashcards

Ch 12/23 Flashcards

Temp regulation

1
Q

homeotherms

A

maintain constant body core temp
* humans are homeotherms
* heat loss must match heat gain - to avoid execessive core body temp - why heat balance is so important

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2
Q

Core temperatures above 45 degrees C can result in:
Core temps below 34 degrees C can result in:

A
  • 45 degrees C can damage proteins and enzymes and lead to death
  • 34 degrees C can result in decreased metabolism, neuron function, cardiac arrhythmias
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3
Q

Thermal gradient

A

exists between deep body core to skin surface
– Typical gradient is approximately 4°C
– In extreme cold, may be 20°C

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4
Q

how is deep body (core) temp measured

A
  • Measured at rectum, ear, or esophagus (Usually in laboratory)
  • Ingestible temperature sensor telemetry system
    (Can be used in athletes during practice sessions)
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5
Q

How is skin (shell) temp measured

A

Thermistors at various locations
– Calculate mean skin temperature

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6
Q

Voluntary vs. involuntary heat production

A
  • Voluntary: exercise - 70-80% energy expenditure released as heat (depends on efficiency)
  • Involuntary: shivering (increases heat production by ~5x) & non-shivering thermogenesis (initiated by thyroxine - thyroid hormone - or catecholamines)
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7
Q

4 mechanisms of heat loss

A
  • Evaporation (most important in hot environments)
  • Radiation: heat lost ot nearby objexts without physically touching them
  • Conduction: heat lost to nearby objects through direct physical touch
  • Convection: heat lost to surrounding air, which becomes warmer, rises and is replaced with cooler air
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8
Q

Evaporation rate depends on

A
  1. temp and relative humidity
    - the higher the temperature and/or humidity, the higher the water vapor pressure = lower rate of evaporation
  2. convective currents around the body: fan or air blowing by you will increase evaporation
  3. amount of skin surface exposed: evaporation much be directly off skin (not clothes) to get the most cooling benefit
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9
Q

heat index

A

body’s perception of how hot it feels
* high relative humidity reduces evaporative heat loss = increased preception of how hot it feels
* relative humidity adds to both preceptions of heat and an actual increase in heat

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10
Q

which avenue of heat loss plays the most important role during exercise in a hot/dry enviornment

A

evaporation

note that evaporation does DECREASE in very hot evironments due to an increased vapor pressure. Though this mechanism will still play a crucial role

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11
Q

What is the body’s thermostat

A

the preoptic anterior hypothalamus (POAH)

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12
Q

how does the preoptic anterior hypothalamus (POAH) respond to heat load (+ its two mechanisms)

A

responds to increases in core temp by
1. stimulating sweat glands to increase evaporative heat loss
2. cutaneous vasodilation so more heat is lost from the skin

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13
Q

How does the preoptic anterior hypothalamus stimulate sweat glands

A

in eccrine sweat glands, Ach binds to mAchR (muscarinic receptor) which stimulates production of sweat

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14
Q

How does preoptic anterior hypothalamus stimulate cutaneous vasodilation

A

same as sweating - Ach binds mAchR causing vasodilation of blood vessels in the skin

not your body will also remove vasoconstricter tone to encourage vasodilation

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15
Q

What do we call the preoptic anterior hypothalamus’s control during increased core body temp

A

sympathetic cholinergic control

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16
Q

What determines heat production during steady state exercise

A

exercise intensity, not environmental temp
* its the intensity NOT the heat

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17
Q

as exercise intensity increases, heat production ____ due to

A

increases due to muscular contraction = increased metabolism generating energy = more heat
* linear increase in body temperature

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18
Q

Core temp increases proportional to what

A

active muscle mass - ie. doing bicep curls will produce less heat than a whole body exercise

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19
Q

Describe

A

Heat production does NOT change, what changes is how we lose heat

as room warms, they relied more on evaporation and less on radiation and convection
- negative radiation & convection = ** gaining heat**

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20
Q

Why is a hot/humid environment so dangerous for exercise

A

humidity/heat makes evaporation harder; environmental heat will result in a shift from radiation/convection mechanisms to evaporation. Radiation and convection can switch if hot enough and give heat back to the body

important to note that enviornmental temp does not determine heat production during exercise but rather can transfer heat back to the body

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21
Q

submax exercise in a hot/humid environment leads to risk of

A

heat illness (heat cramps, then heat exhaustion, then heatstroke) & hyperthermia

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22
Q

Main cardiovascular responses to exercise in heat

A
  • upward drift in oxygen uptake (VO2) - cant maintain steady state
  • cardiac output remains same (see below)
  • HR increase (to compensate for decreased SV)
  • Decrease in SV
  • blood flow directed away from working muscles and nonessential areas to the skin
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23
Q

Sweat rates during exercise in heat

A

higher swear rate
* varies by size of individual (larger = more sweating)
* genetic variation

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24
Q

endocrine responses to exercise in heat

A

increased release of vasopressin and aldosterone to retain blood volume

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25
Q

3 pillars of impaired exercise performance in heat

A

accelerated muscle fatigue can also affect NS and decrease motivation

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26
Q

Ways to prevent exercise-related heat injuries since increases in core body temp with exercise is risky

A
  • hydration
  • less/more breathable clothin
  • heat therapy - acclimating
  • staying out of the heat
  • Frequent rests/cool-down breaks
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27
Q

Acclimation vs acclimatization

What do they both require

A

acclimation: Rapid physiological adaptation that occurs within days to a few weeks, or is artificially induced in a climatic chamber
acclimatization: Gradual, long-term adaptation that occurs within months to years of exposure to the environmental stress (i.e., climate)

BOTH require exercise in hot environment: elevated core temp promotes adaptation (larger response from exercising than just sitting in heat - sauna)

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28
Q

End result of heat acclimation

A

lower heart rate and core temp during submaximal exercise

Note theres a larger improvement to core body temp but will decrease both

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29
Q

5 adaptations from heat acclimation

A
  1. increased plasma volume (10-12%): maintains blood volume, stoke volume, and sweating capacity
    - also dependent on fluid consumption after exercise
  2. Earlier onset of sweating/higher sweat rate: less heat storage, maintain lower body temp
  3. Reduced sodium chloride loss in sweat: reduced risk of electrolyte disturbances
  4. Reduced skin blood flow: able to maintain core body temp better at same intensity
  5. Increased cellular heat shock proteins: prevent cellular damage due to heat
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30
Q

how does the body reduce sodium loss in sweat during heat acclimation

A

different composition of sweat - enhanced aldosterone release causes eccrine gland to reabsorb electrolytes

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31
Q

After heat acclimation and individual will start sweating at a ____ core body temp

A

lower - sweating much earlier

32
Q

how does synthesis of heat shock proteins reduce risk of heat injury

A

protect cells from thermal injury by stabilizing, refolding, and resynthesizing important damaged proteins

33
Q

Number of days required for each component of heat acclimation (HR, plasma volume, precieved exertion, and sweat rate)

A
  1. Heart rate decrease & Plasma volume increase: quickest adaptation (within 3-6 days) - because these are linked - if we have a plasma volume increase we no longer need higher HR to conteract
  2. Perceived exertion decrease: 5-8 days
  3. Sweat rate: slowest - 7-14 day (1-2 weeks)
34
Q

Sex and age differences in thermoregulation and heat tolerance

A
  • when matched for body composition and level of acclimiation, there are sex differences but they are small
  • Aging results in reduced ability to lose heat: skin blood flow redution with age (> 60 years)
35
Q

How fast is heat acclimation lost? why?

A

lost within a few days of no heat exposure
* significant decline in 7 days; complete loss in 28 days
* because maintaining high blood volume is difficult/problematic for the body if not constantly maintaining heat exposure

36
Q

How does the preoptic anterior hypothalamus (POAH) respond to cold

A

responds to decreased core temperature (receptors in the skin/core) by stimulating shivering, cutaneous vasoconstriction, and non-shivering thermogenesis

37
Q

identify the mechanism of heat loss where the body exchanges heat with an object thru physical contact

A

conduction

38
Q

Adaptations during heat acclimatization are important for defending against heat stress. Which of the following is not an adaptation
* increased plasma volume
* earlier onset of sweating
* increased skin blood flow
* increased heat shock proteins
* all of the above are adaptation

A
  • increased skin blood flow: skin blood flow DECREASES due to lower core body temp
39
Q

Mechanism of shivering

A

somatic motor neurons stimulate skeletal muscle contraction = heat production

40
Q

mechanism of non-shivering thermogenesis

A

POAH initiates the release of norepinephrine (catecholamines) and thyroxine which bind to brown adipocyte
* causes increase in rate of cellular metabolism and since mitochondria are inefficient they create a lot of heat

41
Q

How does the POAH induce cutaneous vasoconstriction in the cold

A

release of NE acts on alpha1 adrenergic receptors (a1-ADR) causing vasoconstriction of blood vessels in the skin

42
Q

name the different ligand and receptors involved in vasodilation vs vasocontriction

A
  • vasodilation: Ach binding to mAchR
  • Vasoconstriction: NE binding to a1-ADR
43
Q

Exercise in a cold environment causes (consequences)

A
  • enhanced heat loss
  • may result in hypothermia: loss of judgment and risk of further cold injury
44
Q

Insulating factors

A
  1. subcutaneous fat: especially effective in cold water; primary fuel for shivering in well-fed individuals
  2. clothing: colder weather = need for more layers/insulation
  3. wet vs. dry
45
Q

winchill index

A

similar concept to heat index - windier it is, the colder it feels

46
Q

water immersion on heat loss

A

rate of heat loss = 25x greater than in air of same temperatue - water will disapate heat much faster

47
Q

main cardiovascular response to exercise in cold

A

Cutaneous vasoconstriction - blood flow shunted away from the skin and to the core

48
Q

why is muscle function impared in a cold environment

A

blood flow is shunted away from the skin = reduced blood flow and depressed rate of neural transmission
* results in loss of dexterity and negatively impacts motor skills
* especially in hands and feet

49
Q

Endocrine response to exercising in the cold

A

increased release of NE, E, and thyroxine for metabolic heath production (non-shivering thermo)

50
Q

compared to cold water, exercise in cold air presents less risk of developing

A

hypothermia
* However breathing cold air can trigger exercise-induced asthma because of cooling and drying of airways

51
Q

3 adaptations from cold acclimation

A
  1. lower skin temp at which shivering begins due to increased non-shivering thermogenesis (with less regular shivering)
  2. can maintain higher hand and foot temp due to improved peripheral blood flow (cold-induced vasodilation)
  3. improved ability to sleep in the cold due to reduced shovering
52
Q

Why does cold acclimation cause less shivering

A

heat production is maintained due to increased non-shivering thermogenesis (core temp stays relatively the same)

53
Q

Sex and age differences when responding to cold

A
  • Women show faster reduction in body temp (body composition)
  • similar decrease in body temp between men and women during cold water exposure (properties of disipation)
  • Older (>60) = less tolerant to cold due to decrease in lean muscle mass
  • children body temp falls faster
54
Q

Dalton’s law

A

The total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently (PO2 + PCO2 + PN2)

55
Q

What causes differences in atmospheric conditions

A

partial pressure of Oxygen changes - %O2 in the air does NOT change(20.93%), # of total molecules does

56
Q

Things you could do to prevent altitude sickness

A
  • Hydrate
  • Acclimate
57
Q

Describe the changes in atmospheric pressure and PO2 with increasing altitude

A

at altitude atmospheric pressure decreases and PO2 decreases; diffusion gradient is much smaller ~15 mmHg

58
Q

Effect of hypoxia (altitude) vs. hyperoxia on the hemoglobin-oxygen dissociation curve

A
  • hypoxia/altitude (low PO2) = left shift - to help make it easier to deliver O2
  • hyperoxia (high PO2) = right shift
59
Q

3 things that influence arterial oxygen content (CaO2)

A
  • Saturation
  • hemoglobin concentration
  • Partial pressure of oxygen in arteries (minor contribution since thats what influence dissolved oxygen in the plasma)
60
Q

Physiological responses to exercise at altitude

A
  • decreased VO2max at higher altitude: lower PO2 = lower PaO2 = lower PAO2 and less overall oxygen delivery to muscles
  • Heart rate increases
  • Ventilation increases
61
Q

do trained or untrained individuals have a larger decline in VO2max at alitude

A

Trained
* larger capacity to start with
* higher stroke volume = less transit time

62
Q

Describe the figure that shows the decline in VO2max (capillary PO2 vs capillary transit time)

A

decline in partial pressure with altitude reduces the driving force so that even if transit time is reduced, we wont have full saturation

63
Q

Besides training status, what other factor plays into percent decline in VO2max

A

individual variablility in how we respond to altitude - some respond better to altitude and can maintain a higher % hemoglobin saturation

64
Q

How does HR increase at altitude

A

decreased PIO2 and PaO2 causes adrenals to release epinephrine which
* increases HR, SV, and Q
* Increased vasodilation in the periphery

65
Q

Why does ventilation increase at altitude

A

peripheral chemoreceptors sense lower PaO2

66
Q

how altitude (low PO2) affects sprint and distance running performance

A

Sprints (short-term anaerobic performance): no effect on performance
* relying on non-oxidative sources: O2 transport to muscle does not limit performance
* Lower air resistance may improve performance

Distance (long-term aerobic performance): lower PO2 results in poorer aerobic performance
* Why? Cuz theyre heavily reliant on oxygen for energy production

67
Q

adaptations that happen with acclimatization to high altitude (longer term)

A
  1. Production of more red blood cells: kidneys release EPO = red blood cell production
    * linear increase with altitude
  2. Greater oxygen saturation due to increase in blood flow to lungs
  3. Hyperventilation: increased sensitivity of carotid chemoreceptor
68
Q

Acute cardiovascular response to altitude

A

Decreased plasma volume upon initial
arrival to altitude → decreased SV
* Due to respiratory water loss and increased
urine production → increased hematocrit (no actual change in RBC count, just dehyration)
* normal after a few weeks if adequate fluid is ingestion

69
Q

Describe the physiological processes by which high altitude residents in the Andes adapt to
altitude compared to those who live in Tibet

A
  • Andeans: producing more red blood cells to counter the desaturation caused
    by lower PO2 (hematocrit ~50-65%)
  • Tibetan (Sherpas): increased the oxygen saturation of the existing hemoglobin - high nitric oxide = vasodilation = more blood flow to the lungs
70
Q

Does being born in altitude effect adaptations

A
  • lifetime altitude residents have complete adaptations in arterial O2 content and VO2 max
    – Adaptations are less complete in those arriving at altitude later
71
Q

What can athletes do to most effectively prepare for competition at altitude?
* compete within 24 hrs upon arrival to altitude
* breather hypoxic gases (1-2 hrs per day, 3-5 days) before competing at altitude
* All of the above
* A and C

A

All of the above
* minimizing altitude exposure
* intermittent acute hypoxia - induce helpful physiological changes
* get acclimitized

72
Q

Live high, train low

A

At rest (living) we want to increase altitude response (RBC mass via EPO) and during exercise we want to maintain high interval training velocity (at low altitude)
- traditionally increase RBC mass leads to increased VO2max

73
Q

Some athletes have higher VO2max upon return to low altitude, while other do not- why?

A

could be due to “detraining effect”
- cannot train as intensely at altitude

74
Q

Live low, train high

A
  • avoids negative effects of prolonged alititude exposure
  • No real changes in VO2max or hemoglobin concentration
75
Q

Dealing with problems from training at altitude

artifical “altitude” training

A
  • altitude tent
  • Simulated altitude training pool
76
Q

While there may be no “gold standard” for altitude training, what does each method try to promote

A

increase in blood volume/RBC mass while maintaining training intensity

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