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Hydrostatic Pressure vs Osmotic pressure

Discussion in 'DAT Discussions' started by osimsDDS, Jun 18, 2008.

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  1. osimsDDS

    osimsDDS

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    Can someone PLEASE explain the difference between hydrostatic pressure and osmotic pressure??? It has been bugging me for a while...it has to do with the capillary bed and I know i can just memorize it but I would rather apply it...

    The difference is in the fluid moved in and out of the capillary bed...thanks
  2. theedaddy77

    theedaddy77

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    in the artiole end there is more hydrostatic pressure(pressure for stuff inside the capillarie to go out) because it is closer to the heart, yet once it goes through the capillarie it loses alot of its pressure and it goes down. The osmotic pressure is the pressure from the outside to go into the capillarie.. it is constant. Therefore in the artiole end u have large hydrostatic so pushes stuff out more than what is comming in from the osmotic pressure, and at the venule end u are pushing more stuff in then u are pushing out. Any difference is picked up by lacteals..
  3. harrygt

    harrygt

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    Ok, it's simple. Look at hydrostatic pressure as Blood pressure. Blood pressure is obviously higher in the artery side rather than the venule side.

    Osmotic pressure is what you should already know. Blood has a higher osmotic pressure than the interstitial tissue [or let's say the cells]. HOwever, the osmotic pressure is always constant in the capillary.

    The hydrostatic pressure drives the material out of the capillary, while the osmotic pressure brings the material back to the capillary.
    Hydrostatic pressure is more than osmotic pressure at the artery side, so overall things get out of the capillary. At the venule side, osmotic pressure is higher than hydrostatic pressure, so 90% of the stuff gets back to capillary. the 10% leftover is what gets back to the left subclavian artery by the lymphatic ducts.
    I hope this helps.
  4. HoangDDS

    HoangDDS

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    Hydrostatic pressure is the pressure pushing the fluid out favoring filtration, which is higher at the arterial end of the capillary. Osmotic pressure is the pressure pushing the fluid in favoring absorption, which is higher at the venous end of the capillary.
    Hvpanchal2104 likes this.
  5. harrygt

    harrygt

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    Osmotic pressure is constant, and NOT higher at the venous side. This is a typical mistake. I have also seen a lot of questions about this subject on many bio tests. It's good that the person who asked the question brought this up.
  6. HoangDDS

    HoangDDS

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    You're right harry, thanks for pointing that out. I had to go to my old textbook and double check. So the osmotic force is due to the interstitial fluid concentration of protein, which should be fairly conserved. And it is the difference in hydrostatic pressure (higher at the arterial end of the cap. and lower at the venous end of the cap) that allows for the differences in filtration and absorption. Thanks harrygt.
  7. harrygt

    harrygt

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    I'm glad that you checked it up ! Absolutely right!
  8. theCLE

    theCLE

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    This was extremely helpful. thank you.

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