Physiology 1 Flashcards
What is osmolarity?
Osmolarity is defined as the number of osmoles of solute per liter (L) of solution
What is tonicity?
The effect of a solution on the volume of a cell, determined by the permeability of the cell to the constituents in the solution
What happens when a solution is
a) hypotonic
b) hyper
c) iso
- tonic?
a) Cells will swell
b) Cells will shrink
c) cells will neither swell nor shrink
What are the two major components of total body fluid?
ICF (67%) and ECF (33%)
How is the volume of distribution of a tracer measured using the dilution principle?
Add known dose of tracer to unknown volume of fluid (the body fluid); allow to equilibrate within the body; take a small sample of the fluid and work out how much the tracer has been diluted (dose/sample concentration)
What are the two main ionic constituents of ECF?
Sodium and chloride
Where is most potassium found?
In the intracellular fluid
Why is ICF chloride low?
Negative charge repels it from the negatively charged interior of the cell
How are the ECF/ICF fluid volumes affected by gain or loss of water?
Similar gains/losses of volume from both compartments
Whats happens to ICF/ECF fluid volumes if:
a) gain of salt
b) loss of salt
c) gain/lose isotonic fluid e.g NaCL 0.9%
a) net shift of volume from ICF to the CCF
b) net fluid shift from ECF to ICF
c) change in ECF volume ONLY
Where does most of NaCl loss occur?
In the kidney (urine)
Although the osmolarity of 300mM of urea and 300mM of sucrose is the same, the urea solution is hypotonic and the sucrose solution is hypertonic to red blood cells. Why is this?
Urea is permeable to the RBC membrane and thus is able to “draw” water into the cell
What are the constituents of ECF?
Mostly interstitial fluid (80%)
Plasma (20%)
Lymph and transcellular fluid (very little)
What are useful tracers for:
a) TBW
b) ECF
c) Plasma
a) “heavy” water (3H20)
b) Inulin
c) labelled albumin
What is the main ECF anion?
Chloride
