Osmolarity Flashcards
Average osmolarity of the human body
290 mOsm
o Osmolarity =
g x [C]
g = dissociation constant (how many particles the solute will dissociate into).
g=1 if the solute doesn’t dissociate.
g>1 if the solute dissociates. Remember that most solutes don’t dissociate completely, so g will have a decimal place with it.
[C] = the molar concentration of the substance
Osmotic pressure =
g[C] x σRT
σ - reflection coefficient, a measure of permeability
If σ=0, the solute is completely permeable and osmosis will NOT occur because the solute will diffuse.
If σ = 1, the solute is completely impermeable and osmosis must occur.
• Estimated Osmolality =
(2x [Na]) + ([glucose]/18) + ([BUN}/2.8)