Physiology of Body Fluids Flashcards
define mole
amount of a substance that has a mass equal to its molecular weight- 6.02*10^23
define equivalent
moles/valence. the number of moles that would be necessary if each valence was only 1. for example 1 mole Ca = 2 Eq Ca because of its +2 charge
define molarity
number of moles per liter solutoin
define molality
number of moles per kilogram solvent
under what conditions are molarity and molality the same/different?
similar under dilute conditions but differ w/ significant amount of solids
define osmolality
the total number of particles present in the solution irrespective of chemical nature, molecular weight, valence etc.
define osmotic coefficient
particles in solution may interact with each other, causing their effective removal and a change in osmolality. the extent to which this occurs is characterized by the osmotic coefficient
define osmole
the amount of dissolved substance that exerts the same osmotic pressure as a mole of non-interacting particles
define osmolality/osmolarity
the number of osmoles per unit kg or L of solvent
define effective osmoles
a solute that is impermeable to a membrane
define effective osmolality
the concentration of an effective osmole
oncotic pressure
the effective osmolality caused by proteins in capillaries
reflection coefficient
the probability that the membrane will reflect back the solute
what is the main determinant of the TBW/BW?
fat content- fat is a much lower percentage water
what proportion of TBW is intracellular vs extracellular
2/3 intra, 1/3 extra
describe the distribution of ECFV
20% as plasma volume, 75% in interstitial spaces, 5% in trancellular fluids (CSF/synovial joints/pleural spaces/etc)
what are 2 versions of the 60-40-20 rule?
- 60% TBW/ 40% ICFV/ 20% ECFV
- assume TBW is 60% for men, 50% for women
ICFV is 60% of TBW/ ECFV is 40% of TBW/ 20% of ECFV is PV
how do cells manage to avoid having excessive osmotic pressures that would damage their membranes?
the Na/K moves solute across the membrane to equalize the effective osmolality
what are the two ways in which plasma proteins affect the measured concentrations of electrolytes
- volume effect- proteins take up the most weight
2. protein charge- proteins have a significant negative charge
what is the dominant ECF and ICF cation?
ECF- Na
ICF- K
what is the main determinant of plasma osmolality?
Na
how can you calculate plasma effective osmolality?
2 x [Na] in plasma
what is the osmolar gap?
measured osmolality - calculated osmolality
almost all cells are highly permeable to water d/t aquaporin channels and latent permeability
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