Cell Volume Regulation

Question 1

Osmotic balance

Answer 1

1. ) Chemistry doesn’t matter

2. ) Solutes in ECF must be non-permeating

Question 2

Hypertonic

Answer 2

Water out of cell (cell shrinks)

Question 3

Hypotonic

Answer 3

Water into cell (cell bursts)

Question 4

Nonpermeating solute

Answer 4

Contributes nothing to equilibrium volume of cell. All that matters is presence of non-permeating.

Question 5

Reflection coefficient

Answer 5

Permeating solute does not exert as large of an osmotic force as a non-permeating solute.
How much osmotic pressure depends on how easily it crosses (1/2 as easily as H20? exerts half the ideal osmotic pressure).
Reflection coeff of 1 = non-permable
Coeff of 1 = same as water

Question 6

Clysis

Answer 6

Inject infant with 300mOsM glucose in H20. At first it swells than decreases. NaCl crosses capillaries more easily than glucose.
This is because at first even though solute conc. is the same there is no NaCl in injected bubble so NaCl diffuses out of blood into blister, raising the osmolarity, water moves in, it swells (reflection coefficient across capillaries is higher for glucose than NaCl).
Eventuallys sucrose diffuses and it shrinks.

Question 7

Osmotic pressure and Type I Diabetes

Answer 7

Have excess glucose in blood stream/ECF because no insulin. Give insulin and it falls.
Issue is that brain has lower permeability and if plasma osmolarity flows too quickly the glucose stranded in the brain ECF creates an osmotic gradient and sucks water in, brain swells.

Question 8

Realistic body volumes?

Answer 8

Total 42L, ICF 23L, ECF 14L exchangeable… rest of ECF (5L is inexchangeable)

Question 9

Assumptions

Answer 9

ECF composition is fixed, only H20 can change volume, osmolarity, conc out = conc in permeability

Question 10

Calculating OsM

Answer 10

multiple by number of ions dissociated. so 100mM CaCl2 is x3 and 100mM NaCl is x2.
100mM glucose does not dissociate so it’s 100 still.
100mm glucose + 100mM NaCl = 300.

Question 11

Calculating mEq

Answer 11

For K2S04 the K+ meq is 200, S04 is 200.
for 100mM caCL2 its Ca++ is 200, Cl- is 200.

Multiply by VALENCE.

Question 12

Which way does uncharged solute move?

Answer 12

According to concentration gradient.

Question 13

Osmosis vs. diffusion

Answer 13

Diffusion: random thermally agitated movement of molecules
Osmosis: net inward movement of water across a semi-permeable membrane (permeable to solvent NOT solute). Basically the diffusion of H20.