BIOL 2P93 Lecture Notes - Specific Gravity, Osmotic Concentration, Osmotic Pressure
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Published on 4 Feb 2013
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Physiology of Body Fluids—Summary
I. Physiochemical Properties of Electrolyte Solutions
a. Molarity—amount of substance relative to its molecular weight (mol/L)
i. (X gr)*(Y L) / ( Z gr/mol) = A mol/L
b. Equivalence—refers to stoichiometry of interaction between cation & anion;
determined by the valance of these ions
i. (X mol/L) * (Y Eq/mol) = Z Eq/L
ii. number of Eq/mol determined by the charge (Ca=2, Na=1, etc)
c. Osmosis—movement of water across a membrane due to osmotic pressure diff.
i. Osmotic pressure (Π)—colligative property of solution determined by the
number of solute particles in solution: Π=nCRT (atm) (1atm=760 mmHg)
ii. Osmolarity—number of solute particles per L of H2O
1. Osmolarity = [concentration]*(number of dissociated particles) =
[X]*n where 0<= n =<1
2. temperature dependent
iii. Osmolality—number of solute particles per 1 kg H2O (Osm/kg H2O)
1. not dependent on T => used more frequently for physiology
d. Tonicity—effect of a solution on cells’ volumes
i. Hypertonic—causes cell to shrink
ii. Hypotonic—causes cell to swell
iii. Isotonic—doesn’t change cell volume
e. Oncotic Pressure—osmotic pressure generated by lg. molecules (esp. proteins)
in solution; not a major force when considering H2O movement across cell mems
f. Specific Gravity—total solute concentration found by dividing wt. of a volume
of solution by equal volume pure H2O
i. Specific gravity of urine often measured in clinical settings
ii. Tells number of solute particles based on their weight
II. Fluid Exchange between body fluid compartments
a. Osmotic Pressure & hydrostatic pressure determine movement of H2O from
capillaries to interstitum & back
b. Capillary hydrostatic pressure (Pc) is high at beginning & low at end of capillary
bed => movement of H2O out of capillary
c. High oncotic pressure in capillary @ end of capillary bed => movement of H2O
into capillary
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