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Thread: Body Fluid Compartments

  1. #1
    PharmD Year 1 TomHsiung's Avatar
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    Default Body Fluid Compartments

    Approximately 60% of the body weight is made up of water, which is distributed into various aqueous spaces in proportion to their osmotic content.

    The collective volume of all the cells in the body is called the intracellular fluid (ICF). It contains roughly two thirds of the body osmotic content, and therefore two thirds of the water. The remaining one thirds of the osmotic content and water is called the extracellular fluid (ECF). It is mostly interstitial fluid and blood plasma. Because of the ease with which water crosses most cell membranes the ECF and ICF are in osmotic equilibrium.

    If the addition or loss of fluid is isotonic sodium, only the volume of the ECF is affected, but if the fluid is either hyper- or hypo-osmotic, both compartments change volume. The addition of water along expands both the ICF and ECF. Adding sodium chloride without water does not change the total volume, but causes a shift of water from the ICF to the ECF in orders to restore equality of osmolality between the 2 compartments.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  2. #2
    PharmD Year 1 TomHsiung's Avatar
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    Default Re: Body Fluid Compartments

    Water permeability of different tubule segments

    Proximal tubule
    Tight junctions (significantly permeable) and luminal membranes (highly permeable)

    Early parts of the descending thin limb
    Tight junctions (-) and luminal membranes (very high water permeability)

    Ascending limbs of Henle's loop (both thin and thick)
    Tight junctions (relatively water impermeable) and luminal membranes (relatively water impermeable)

    Distal convoluted tubule
    Tight junctions (relatively water impermeable) and luminal membranes (relatively water impermeable)

    Collecting-duct system
    Tight junctions (-) and luminal membranes (intrinsically low but can be regulated so that it increases substantially)
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

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