Thermoregulation Flashcards
What is the role of skin
More dilation and more flow at superficial area
Carry it to peripheral to cool you down
Heat loss =
heat gain
Core Temp
37 C or 98.6 F
Abdominal, thoracic, cranial cavities
Measured orally, esophageal, rectal, tympanic mem, pill
Skin Temp
34 C
Measured by weighted sum from different regions of the body
We adjust this to maintain core temp
Body temp is combo
of skin and core temp
Clinically significant core temp
above 38.5 will see symptoms
athletes can get to 40 and feel just fine though
Clinically significant skin temp
around 45
Heat Stroke
Core temp - 40.5
Heat exhaustion
Core temp 38.5 - 39.5
Mechanisms of heat gain and loss
Metabolic Rate Radiation Conduction Convection Evaporation
Metabolic Rate
ONLY heat gain
Shivering to warm you up
The higher it is, the higher the heat gain
Radiation ***
Heat gain from sun
Heat loss sitting in classroom (we radiate to the environment)
Conduction
Through direct contact
Heat gain if touch heater
Heat loss if sit on cold seat
Convection ***
Heat gain or loss but from skin surface to a moving liquid or gas
Ex: fan behind the heater
Evaporation
Heat loss ONLY
water conversion from liquid to vapor
Evaporation requires
vapor pressure gradient
Sweating ____ result in heat loss, evaporation must occur - depends on
does NOT
SA exposed
Wind speed
Relative humidity (primary factor)
Inability to lose heat by evaporation results in
higher core temp
higher sweat rate
How is body temp sensed
Central thermoreceptors - located in POAH, sensitive to heat
Peripheral thermoreceptors - sensitive to cold
Hypothalamus has a set point (POAH) - will cause sweat glands to secrete when core temp inc
Effector Response - Cold
VC
Piloerection
Shivering
Non shivering –> thyroxin release
Effector Response - Heat
VD
Sweating an evaporation
Reflex to cold
Peripheral thermoreceptors –> adrenergic –> NE –> VC
Reflex to heat
Central thermoreceptors –> cholinergic –> Ach –> VD
Neural control of Cutaneous innervation
Dual sympathetic innervation
Adrenergic = VC
Cholinergic = VD
At rest what tone is on muscle
adrenergic have some tone on muscle so when you get hot, you withdraw the symp adrenergic tone and that causes passive dilation that doubles flow and then you activate cholinergic that causes huge (6 fold) inc in flow and cholinergic is also stimulating sweat response to cool you down
Distribution of CO when hot
CO will Inc. (SV dec and HR Inc)
When hot, there is a lot going to the skin
Submaximal exercise in the heat for absolute workload CO - what will decrease
CO SV MAP Central blood volume (most in skin) TPR
Submaximal exercise in the heat for absolute workload CO - what will increase
avO2 difference
Rectal temp
HR
Exercise + Heat + Dehydration and muscle blood flow
SV may decrease to maintain CO
Inactive tissue compensates (splanchnic)
Skin is next
Active muscle will eventually help compensate
Other systems at work during exercise
Angiotensin II –> VC –> Inc BP
Angiotensin II stimulates thirst centers
Aldosterone stimules sodium reabsoprtion
Why is hydration state important during exercise
poorly hydrated athlete can’t perform at his/her peak
When we get thirsty..
Already dehydrated - dehydration preceeds thirst
2% of body weight dehydrated before feeling thirsty –> decline in performance
What happens when athletes are dehydrated
Blood volume shrinks Skin blood flow is less Muscle blood flow is less Temperature rises Fatigue Blood Pressure Dec Lightheaded Syncope Hyperthermia
What makes athletes drink more fluids
inc by 45% when flavoring is added to water
Additional inc by 46% when flavor contained NaCl
Dehydration imposes
Thermal and CV stress
Heat Cramps
Associated with Na, K losses
Pulls water from cells to ISF
Heat Exhaustion
Dizziness, extreme fatigue, vomiting, faintain, tachycardia, hypotension, profuse sweating
Volume loss that is more than high core temp
Treat with cooling, fluid and electrolyte replacement
Heat Stoke
Rising core temp, cessation of sweating, hot and dry skin, hypotension, confusion or unconsiousness
Treatment = immediate rapid cooling - ice immersion
Preventing Heat Injury
Plan events when environmental conditions are best
Recognize symptoms
Water availability
Acclimation
Heat Acclimization
After known history of heat illness, acclimation is most important predictor of heat tolerance
Most critical component in heat acclimation
expansion of plasma volume