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WATER IS 50% OF BODY WEIGHT IN WOMEN

60% IN MEN

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FLUID DISTURBANCES

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Intracellular fluid (ICF)

• Largest compartment – 60%• Main cation – potassium• Anions - phosphates and bicarbonate

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ECF = 40%

• Main cation – sodium• Anions - chloride and bicarbonate

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If 1 L of solute-free water is lost from the body, how much fluid is lost by the ICF compartment?

Water ICF : ECF = 2:1 ratioSolute-free water loss

Twofold greater reduction in the ICF compartment than the ECF compartment

Volume loss ICF = 667 mL ECF = 333 mL

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Lose of 1L of iso-osmotic fluid

ECF compartment will decrease by 1 L Na+ is largely restricted to the ECF

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Osmolality and osmolarity

Often used interchangeablyOsmolality

Number of solutes per mass of water Osmolarity

Number of moles of solute in a liter of solution

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Solutes

Extracellular and intracellular solutes (or osmoles) Markedly different

Water Moves across cell membranes Distributes between ICF and ECF

Until the osmolality is the same

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