Hot Environments Flashcards
at temperatures above 30C what method of heat loss is important
above 30C heat loss by radiation, conduction and convection become ineffective. EVAPORATIVE cooling becomes most important
two types of sweat gland
apocrine and eccrine
apocrine sweat gland
- armpits, genital,ears
- no role in thermoregulation
- low number and large diameter
- secretion rich in lipids and carbohydrates
- close to hair follicles and sebaceous gland (hair condition)
eccrine sweat gland:
-high number & small diameter (50-100 microns)
-responsible for sweat production
150-340/cm2
-changes in populations (eskimos more in cheeks, less in thorax)
components of eccrine sweat gland
- Acinus region: primary secretion of a protein-free filtrate
- Duct: Absorption of Na+ and Cl-
- Pore
- under sympathetic control (colonergic secretion, acetylcoline neuro transmitter)
- GPCR receptor, Gq couple pathway
basal lateral (blood side) key transporters in Acinus
- basal lateral membrane:
- -Na+ K+ ATP ase pumps sodium out of cell, keep sodium inside the cell low
- -NKCC (sodium potassium 2 chloride transforter) moves 1 K+, 1 Na+, 2 Cl- and water into cell
- potassium channel to move it out = recycle
= gradient for chloride for Chloride to be secreted into lumen
apical membrane key transporters in Acinus
- chloride channel, chloride moves into lumen == hypertonic condition in the lumen
- negative potential in lumen allowing for movement of Na+ (paracellular)
-also urea and lactate moved into lumen
ENDS being isotonic though (aqua porin 5)
apical membrane key transporters in duct
- ENAC (NA+)
- CFTR (Cl-) REABSORPTION FOR BOTH
basal lateral membrane key transporters in duct
- Na+ K+ ATPase pump (sodium out of cell)
- K+ channel (out)
- Cl- channel (out)
eccrine and cystic fibrosis:
defect in CFTR channel, reabsorption of Na+ and Chloride in DUCT cells = large vol of salty sweat
high levels of aldosterone (hormone) will up-regulate
ENAC
sweat salinity varies with
flow rate
optimum sweat flow to reduce Na+ and Cl- loss
5mL/[min.m2]), increase flow rate = less Na and Cl removed (overload ENAC and CFTR channels)
normal conditions can produce __ litres sweat/ hour
1.5
once acclimatisation has taken place you can produce up to __ litres/hour
4 so we must adapt!
sweat is ___, so you lose solute free water
hypertonic
-reducing cell volume and raising osmolarity in the cells
why is it crucial for the body to adapt to increased temperatures?
as pre-adaption u can lose 30g of salt/day in sweat, post adaption this drops to a few grams/day = large volumes of v dilute sweat
acclimatisation steps:
1) decrease sweating threshold (temp u start to sweat becomes lower)
2) increased volume of sweat
3) reduced osmolarity of sweat
4) decrease in HR
5) increase in total blood volume
-> over about 14 days
acclimatisation: reduction in sodium being lost is due to an increase in
aldosterone production, which up regulates ENAC Na+ channel
changes in sweating pattern:
through acclimatisation overall volume of sweat increases but also increase in legs and arms massively after adaptation (legs and arms have high SA)
rate of heat loss by evaporation =
evaporative heat-transfer coefficient X (H2O vapour pressure of skin - H2O vapour pressure of environment) X SA
Desert :
environment water vapour pressure V low –> easy for sweat to evaporate
Rainforest :
Very high humidity –> water vapour pressure high, harder for sweat to evaporate
3 problems with hot environments:
- heat cramps
- heat collapse
- heat stroke
Heat cramps:
cramping in calf/ abdomonal muscles
- muscles contracted and not able to relax
- loss of sodium, calcium and magnesium
heat collapse:
- 38.5-40 core temp
- huge vasodilation to periphery , effect on blood pressure and amount of blood going to brain
- sweating maintained
why is it better to rehydrate by isotonic solutions not water
water just dilute,
heat stroke
- 41 degrees core
- peripheral vasoconstriction, harder to get heat loss from body
- after big loss of fluid from the body
- no sweating
