Thermoregulation Flashcards
Humans are homeotherms meaning:
they maintain a constant core body temp
What is normal core temp?
37C or 98.6F
Temperatures above 45C or 113F can:
damage proteins and enzymes and lead to death
Temperatures below 34C or 93.2F can:
result in decreased metabolism and cardiac arrhythmias
Ideal thermal gradient from body core to skin surface is:
4C or 7.2F; best to keep it close together
Hypothalamus increases the body’s temp set point and creates a fever due to:
pyrogens like proteins or toxins from bacteria or virus
What indicates the onset of a fever?
shivering
What indicates the end of a fever?
sweating
During exercise, heat moves from:
body core to body shell via blood
What are three ways to measure deep-body (core) temp?
rectum, ear, or esophagus
What is the gold standard way to measure core body temp?
rectum
What can be used to measure an athlete’s body temp during exercise?
ingestible temp sensory telemetry system
What is the issue with ingestible temp sensory system?
never know where it’s at in the body which can change internal core temp readings
What is the best way to accurately take skin temp?
calculate mean skin temp, take seven readings of temp around the body
During rest, metabolic heat production is:
small
An example of voluntary heat production is:
exercise; 70-80% energy expenditure released as heat
What is an example of involuntary heat production?
shivering, increases heat production by approx 5x
What hormones are involved in non-shivering thermogenesis?
thyroxine and catecholamines
What structure is considered the body’s thermostat?
hypothalamus
In the absence of Ca2+, this structure covers actin-binding sites
tropomyosin
Describe the difference between systolic time and diastolic time at rest. What happens to these phases of the cardiac cycle during exercise?
at rest: diastolic time is longer than systolic time
during exercise: the duration of both will decrease but systolic time is longer overall
Radiation
transfer of heat via infrared rays
Conduction
body heat loss due to contact with another surface
Convection
heat transferred from body to air or water
evaporation
heat loss due to phase change from liquid to gas
What are the three things that evaporation rate depends on?
- temperature and relative humidity
- convective currents around the body
- amount of skin surface exposed to the environment
What is the primary heat loss method during exericse?
evaporation (sweat)
What is something in the environment that can impact evaporation during exercise?
humidity
Which nervous system acts on skin arterioles during both cold and hot exposure?
Sympathetic Nervous System
What does the SNS do for heat loss when it is cold/hot?
cold: vasoconstriction minimizes heat loss (think of constriction>holding your arms tight to yourself because its cold)
hot: vasodilation enhances heat loss (think of dilation>opening up>spreading out bc its hot)
What is the primary type of sweat gland?
eccrine sweat gland
Explain how the eccrine sweat gland affects heat loss
SNS releases acetylcholine on the gland causing sweat to be released which leads to heat loss via evaporation
The eccrine sweat gland is more responsive to changes in:
core temperature
Hypothalamic Response to Heat Stress
- Heat stress increases body temp
- Thermal receptors in the body core and skin send signals to the hypothalamus
- Hypothalamus initiates signal causing SNS to increase sympathetic activity
- Skin vasodilation and sweating
When exercising in the heat, skin arterioles ___ to increase heat loss.
dilate
When skin arterioles dilate for long periods of time, blood can start to ___ causing:
pool; SV and venous return to decrease
When exercising in the heat, blood volume ___
decreases
What is cardiovascular drift?
HR progressively increases during steady state exercise in the heat to compensate for blood volume loss via sweat
Heat production that is not lost is stored:
in body tissues
As exercise intensity increases:
- heat production increases
- linear increase in body temp
- core temp increases proportional to active muscle mass
- increased reliance on evaporative heat loss
As ambient temp increases:
- exercise-induced heat production remains constant
- lower convective and radiant heat loss
- higher evaporative heat loss
Energy output increases as:
workload increases
When exercising in heat, convective and radiative heat loss becomes:
less and less effective
Heat index is the measurement of:
body’s perception of how hot it feels
What is the best way to measure heat index?
Wet bulb globe temperature
What is a sign of the start of heat illness?
heat cramps
When someone experiences heat cramps, should you pull them from exercise?
yes
What are heat cramps?
- least serious of three heat illnesses
- severe, painful cramping of large muscles
- triggered by Na+ loss, dehydration
- most common in heavy sweaters
- prevented by liberal intake of Na+, water
Which heat illness is a sign that things are going downhill quickly?
heat exhaustion
What is heat exhaustion?
- accompanied by fatigue, dizziness, nausea, vomiting, fainting, weak and rapid pulse
- caused by severe dehydration from sweating
- simultaneous blood flow needs of muscle met due to low blood volume
- thermoregulatory mechanisms are functional but overwhelmed
During heat exhaustion, are thermoregulatory mechanisms still working?
yes, but they are overwhelmed
What would someone’s pulse who is suffering from heat exhaustion look like?
rapid and weak
What is the most serious heat illness?
heat stroke
What is best for dealing with heat stroke?
putting person in an ice bath with convection
Will someone suffering from heat stroke be sweating?
no
During heat stroke, are thermoregulatory mechanisms working?
no
What will the pulse of someone suffering heat stroke feel like?
strong and rapid
What is heat stroke?
- life threatening, most dangerous
- thermoregulatory mechanisms fail
- characterized by core temp >40C (104F) and confusion, disorientation, unconsciousness
- if untreated, results in coma, unconsciousness, and death
- must cool whole body ASAP
- recent heat illness compromises the body’s ability to deal with heat making heat stroke more likely
What is heat stroke characterized by?
core body temp over 40C (104F) and confusion, unconsciousness, and disorientation
Ways to prevent heat injuries:
- exercise during cool hours
- lower exercise intensity and/or duration
- expose skin
- frequent rests
- frequent water breaks
To prevent dehydration during exercise:
- hydrate prior
- consume 150-300 mL fluid every 15-20 mins
- monitor urine color
What are the causes of exercise performance impairment in hot environments?
- accelerated glycogen metabolism
- increased free radical production
- reduced muscle blood flow due to increased skin blood flow and sweating
- high brain temp reduces neuromuscular drive
What is the consequence of accelerated glycogen metabolism?
increased lactate accumulation
What is the consequence of increased free radical production?
damage to muscle contractile proteins
What is the consequence of high brain temp that reduces neuromuscular drive?
reduction in motor unit recruitment (central fatigue)
What are the three factors that contribute to impaired exercise performance in the heat?
- central nervous system dysfunction
- cardiovascular dysfunction
- accelerated muscle fatigue
What is heat acclimation?
- rapid adaptation to environmental change
- elevation of core temp promotes adaptation
What is a heat acclimation training plan?
- exercise in heat for 10-14 days
- low intensity and long duration for 80-100 mins per day
- moderate intensity, short duration for 30-35 mins per day
Acclimation is lost within:
a few days of inactivity or no heat exposure, significant after 7 days, complete loss after 28 days
What are some adaptations during heat acclimation?
- increased plasma volume
- earlier onset of sweating and higher sweat rate
- reduced sodium chloride loss in sweat
- reduced skin blood flow
- increased cellular heat shock proteins
Hypothermia is determined by a body temp below:
35 degrees celcius or 95 degrees F
During cold stress, heat loss is ___ than heat production
greater
Hypothalamic response to cold stress
- cold stress decreased body temp
- body core and skin neural thermal receptors send signal to the brain (hypothalamus)
- hypothalamus initiates signal causing sympathetic nervous system (SNS) to increase sympathetic activity
- effects act (shivering, decreased blood flow, increased thyroxin and sympathetic catecholamine release
What is cold stress?
environmental condition that threatens temp homeostasis by decreasing core temp
What are some physiological responses to exercise in the cold?
- low core temp > slow HR
- muscle function decreased
- superficial muscle fibers numbed
- as fatigue increases, metabolic heat production decreases
Windchill factor takes into account:
air temp and air movement (wind)
The lower the windchill factor value, the ___ the chance of freezing tissues
higher
Heat loss is __x faster in cold water versus cold air
4x
Heat loss is ___ in moving water
increased
Hypothermia from cold water occurs well above ___ ___
freezing point (0 celcius)
What is the treatment for hypothermia?
- get person out of the cold
- remove all wet clothing
- provide warm drinks and dry clothing
- put person into sleeping bag
- find a source of heat
- prepare for emergency treatment and/or evacuation
- may require hospital facilities
What are two health risks during exercise in the cold?
- frostbite
- exercise-induced asthma
What is frostbite?
- peripheral tissue freezing
- excess vasoconstriction > lack of O2 nutrients > tissue death
What happens if frostbite goes untreated?
gangrene (tissue death/rotting), tissue loss
How do you treat frostbite?
gradually rewarm only when no risk of refreezing
Exercise-induced asthma is caused by:
excessive airway drying
Exercise-induced asthma is treated by:
steroid inhalers
Cold related illness mitigation strategies:
- dress in layers and remove as you warm-up
- stay dry
- avoid prolonged cold exposure after exercise
What changes allow your body to acclimate to the cold?
- lower skin temp at which shivering begins (increased non-shivering thermogenesis)
- maintain higher hand and foot temp
- adaptations begin in one week
