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Flashcards in Body fluid Deck (17)
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Divi up the total body water

60% of wt is TBW = 42L
40% of wt is ICF
20% of wt is ECF
ECF = 3/4 interstitial + 1/4 plasma


What's the "dilution principle"?

We are able to determine fluid volume based on measuring the amount of solute and then its concentration after it has diffused.


If your patient has an acute change in body weight over a brief period of time, what is most likely causing this change?

change in TBW


the mEq of a fluid compartment is based on _______________

Valence charges

(Na+ = 1mEq, where Ca++ = 2mEq)


Since all fluid compartments are electrically neutral, what does the body do to compensate when you have a higher humber of mEq's in one compartment?

Balances with proteins (negative charge)

(Intracellularly, you have more Ca++ and Mg++, so you also have more protein to balance)


__________________ is the concentration of discrete, osmotically active particles in solution.

Osmolality. (mOsm/kgg H2O)

Particle mass, charge, and size do NOT matter


True or False: Body fluid compartments are in osmotic equilibrium.



What is a normal osmolality?

275-300mOsm/kg H2O. (Typically use 290)


The volume of fluid compartments depends on _____________

# of osmotically active particles


If you add pure water to the body, what happens to it, and what happens to your osmolality?

Both ICF and ECF expand, Osm falls


If you add isotonic NaCl to your body, what happens to the fluid compartments? What happens to osmolality?

Only the ECF expands, no change in Osm


If you add pure NaCl to your body, what happens to the fluid compartments? What happens to osmolality?

The ECF expands, the ICF shrinks and Osm increases.


The plasma osmotic pressure is __________the osmotic pressure of the interstitium. Why?

(less than, equal to, greater than)

greater than! This is due to the hydrostatic pressure in the blood vessels which offsets this osmotic pressure difference


Explain the Starling Hypothesis

Hydrostatic pressure in the capillaries is bigger on the arterial side and pushes fluids out of the capillaries. Eventually, there's not so much fluid volume in the capillaries, but still lots of solute. So the osmotic pressure pulls water back into the capillaries on the venous side.


________ is abnormal expansion of the interstitial fluid compartment



If you notice localized edema in your patient, what is the cause?

Starling's forces are unbalanced. Fluids are moving into the interstitium, but not being pulled back in.

(ex: DM pts have low protein, so no proteins to create osmotic pressure)


If you notice generalized edema in your patient, what is the cause?

Kidneys aren't excreting NaCl. (water follows salt due to osmotic principles)