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can someone explain osmotic pressure to me? I know what hypo/hyper/isotonic is and WHY water movies into solution with more solute but what is the relation to osmotic pressure?
osmotic pressure
- Thread starter Farcus
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I have some difficulty with this concept as well, but I can try.
Osmotic pressure = MRT where M is molarity (mols solute/L solution), R is gas constant, and T is temperature (K). As you mentioned, water tends to move from low solute concentration to high solute concentration (diluting the solute wherever it is). Osmotic pressure is simply the pressure the solute particles exert back when water flows into a compartment containing the solute particles (which cannot flow into the compartment of pure water) for example. You see the relationship between osmotic pressure and molarity in the equation above; the greater concentration/molarity of particles you have, the greater the osmotic pressure they exert.
I think a capillary example illustrates this particularly well. In a capillary, filtration (fluid flowing from the blood stream to the interstitial space (ISF space)) generally predominates on the arterial end. Absorption (fluid flowing from ISF space to the blood stream) predominates on the venous end. Why is this? Basically, you have a balance of forces/pressures governing which end filters and which end absorbs.
Pressures:
1) Capillary hydrostatic pressure - generated by pumping heart which pushes the blood through capillaries. This favors filtration into the ISF space.
2) Capillary osmotic pressure - pressure exerted by interstitial fluid solute particles to push fluid back into blood stream.
3) Interstitial fluid osmotic pressure - pressure exerted by plasma protein/solute particles to push fluid into the ISF space.
The hydrostatic pressure is greater on arterial end than the capillary osmotic pressure; the ISF osmotic pressure is small on both ends and doesn't affect the overall balance significantly. This tilts balance in favor of filtration (fluid flows into ISF).
The hydrostatic pressure is smaller on venous end than the capillary osmotic pressure; again ISF osmotic pressure is not significant here. This tilts balance in favor of absorption (fluid flows into bloodstream). Problems occur when this natural balance goes awry (clot forms in the venous end -> increase in hydrostatic pressure on end that should have small hydrostatic pressure -> increased filtration and possible edema.)
So basic principle: Increased concentration of particles = increased osmotic pressure (which makes sense since more particles = more force/pressure on the compartment walls).
If anyone sees something wrong with this description, please feel free to correct me. Hope that helps!
Osmotic pressure = MRT where M is molarity (mols solute/L solution), R is gas constant, and T is temperature (K). As you mentioned, water tends to move from low solute concentration to high solute concentration (diluting the solute wherever it is). Osmotic pressure is simply the pressure the solute particles exert back when water flows into a compartment containing the solute particles (which cannot flow into the compartment of pure water) for example. You see the relationship between osmotic pressure and molarity in the equation above; the greater concentration/molarity of particles you have, the greater the osmotic pressure they exert.
I think a capillary example illustrates this particularly well. In a capillary, filtration (fluid flowing from the blood stream to the interstitial space (ISF space)) generally predominates on the arterial end. Absorption (fluid flowing from ISF space to the blood stream) predominates on the venous end. Why is this? Basically, you have a balance of forces/pressures governing which end filters and which end absorbs.
Pressures:
1) Capillary hydrostatic pressure - generated by pumping heart which pushes the blood through capillaries. This favors filtration into the ISF space.
2) Capillary osmotic pressure - pressure exerted by interstitial fluid solute particles to push fluid back into blood stream.
3) Interstitial fluid osmotic pressure - pressure exerted by plasma protein/solute particles to push fluid into the ISF space.
The hydrostatic pressure is greater on arterial end than the capillary osmotic pressure; the ISF osmotic pressure is small on both ends and doesn't affect the overall balance significantly. This tilts balance in favor of filtration (fluid flows into ISF).
The hydrostatic pressure is smaller on venous end than the capillary osmotic pressure; again ISF osmotic pressure is not significant here. This tilts balance in favor of absorption (fluid flows into bloodstream). Problems occur when this natural balance goes awry (clot forms in the venous end -> increase in hydrostatic pressure on end that should have small hydrostatic pressure -> increased filtration and possible edema.)
So basic principle: Increased concentration of particles = increased osmotic pressure (which makes sense since more particles = more force/pressure on the compartment walls).
If anyone sees something wrong with this description, please feel free to correct me. Hope that helps!
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Actually its P = iMRT, where i is the van't hoff factor, which is the number of particles a solute will dissolve into in solution. Ex: NaCl has a van't hoff factor of 2, because it becomes Na+ and Cl-. THis comes into effect if you're measuring the osmotic pressure of say glucose vs. NaCl. If you have two solutions at the same molarity, the NaCl will have the higher osmotic pressure because of the i = 2, so the water will move towards the solution with NaCl.
Ahh, good call. I usually just remember to look for the number of particles a compound breaks up into i.e. NaCl -> 2, CaCl2 -> 3, H2SO4 -> 3 and multiply after I get the pressure. But that is a great point, thanks for catching that.
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