Fluid Physiology Flashcards
What is diffusion
Movement of solute from high conc to low conc through solute permeable membrane
What is osmosis
Movement of water from high conc to low conc until solute concentrations are equalized on both sides of solute impermeable membrane
What is osmolarity
Measure of solute concentration per unit VOLUME of solvent (1L)
What is osmolality
Measure of solute concentration per unit MASS of solvent (1kg)
Only solvents that contribute to osmotic pressure / can’t cross membrane - Na, glucose, urea, alcohol
What is osmolality in ICF and ECF
285-290
Why is osmolality used instead of osmolarity in labs
Mass does not vary with pressure but volume does
What does osmolarity determine
The osmotic pressure and how the solvent will diffuse across membrane
What is tonicity
The measure of the osmotic pressure gradient between two solutions separated by semi-permeable membrane determining the extent of diffusion
Only takes into account solutes that CANNOT cross
What is TBW in average 70kg man
42l
What is volume of water in intracellular space
28l (2/3)
What is volume of water in extracellular space
14l (1/3)
What proportion of water in the extracellular space is intravascular
3l (20%)
What is BP determined by
Volume in intravascular space
In the extracellular compartment what moves to maintain gradient
Small ions and water
Large CANNOT cross
Water moves to equilibrate the osmolarity increasing or shrinking the volume of set spaces
Why do people with low protein leak water
Low protein = high water and water will move from high to low concentration leading to oedema
