Human Physiology Body Water and Osmosis
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How do you calculate Total Body Water (TBW)?
TBW = 0.6 x body mass
(a person is approx. 60% water)
What factors account for variation in TBW?
Primarily fat composition, but also muscle composition to a lesser degree AND it varies greatly with age (especially in kids)
ECF = _______ TBW
ICF = _______ TBW
ECF = 1/3 TBW
ICF = 2/3 TBW
Plasma = ________ ECF
Interstitial fluid = _________ EFC
Plasma = 1/5 ECF
Interstitial fluid = 4/5 ECF
How does water move between ECF and ICF compartments?
the cell membrane and capillary wall are quite permeable to H20 via aquaporins.
Water will move IF there is a difference in osmolarity
"Water goes where the osmolytes are"
Water moves from its area of high concentration to low through semi-permeable membranes
osmoles / kg solvent
osmoles / L solution
Define OSMOTIC PRESSURE
(π=RTC) the amount of external pressure needed to prevent the entry of water
- π is osmotic pressure
- R is universal gas constant
- T is temp in K
- C is solute concentration in Osm/L
(aka anti-diuretic hormone) released by brain and changes aquaporin activity in the kidneys to pull water back into the body
released by adrenal cortex and increases Na+ reuptake in kidney (and water, which follows Na+)
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