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!