Human Physiology Body Water and Osmosis

TBW = 0.6 x body mass

(a person is approx. 60% water)

Primarily fat composition, but also muscle composition to a lesser degree AND it varies greatly with age (especially in kids)

ECF = 1/3 TBW

ICF = 2/3 TBW

Plasma = 1/5 ECF

Interstitial fluid = 4/5 ECF

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

(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⁺)