Medical Knowledge Flashcards
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What is Osmotic Pressure
How is it different to Hydrostatic pressure?
“Osmotic pressure (π) is a thermodynamic quantity: the mechanical pressure that would be required to prevent net water entry across a semipermeable membrane.
Hydrostatic pressure (P) is the actual mechanical pressure a fluid exerts on its container.
In a rigid, volume-fixed osmometer the inflow of water has no room to expand the chamber, so the hydrostatic pressure rises until P = π and flow stops. In a compliant chamber (e.g., a typical animal cell) the same osmotic drive is relieved mainly by swelling; hydrostatic pressure increases only minimally even though π has the same numerical value on paper. Thus π and P are distinct properties that coincide in value only when volume cannot change—much the way a boiler’s steam pressure is a purely hydrostatic property, not an osmotic one.
