Dr. Baylis - Body Fluids Flashcards
TBWater breakdown?
60% of bodyweight = total fluid
40% of bodyweight = intracellular fluid
20% of bodyweight = extracellular fluid
15% of bodyweight = interstitial fluid
5% of bodyweight = plasma
What is the dilution principle?
V = (X - Excretion) / (Concentration)
How do we measure just plasma amount?
Use 131 Iodine-labelled albumin or EVANS BLUE dye which binds to plasma proteins and stays in plasma
How do we measure ECF?
This means we must use something the equilabrates through the plasma and interstitial space. We us inulin a sugar which is foreign to the body.
How do we measure total body water.
We need something that acts just like water and crosses both the cappilary walls and the cell membrane equilabrating throughout. We us D2O.
How to calulate ICF?
Calculate TBF and subtract ECF.
How does pressure work along capillary walls?
Osmotic pressure is higher at the beginning of the capillary. This forces H2O our of the capillary. Later in the capillary the oncotic pressure increases as the osmolarity in the capillary rises and this forces H20 back into it. Over the course of a capillary the H2O xfer is equal.