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Cell Section Q&A1

1. The administration of an IV glucose solution (about 50 g/L/iso-osmotic to plasma) is equivalent to administration

of pure water (because glucose is metabolized). If a subject received 3 liters of isotonic glucose solution, how did

the water (in liters) distribute between the ECF and the ICF?

ECF ICF

a. 0 3

b. 1 2

c. 1.5 1.5

d. 2 1

e. 3 0

Cell membrane is permeable to water flows in and out. Water diffuses through water pores and through lipid

bilayer. 1:2 because of water/bulk distribution in the body.

2. Your patient has a low concentration of dissolved oxygen in the blood. The attending physician correctly

recommends that you increase the O2 concentration in order to prevent further cell damage due to hypoxia. This

treatment is appropriate because the main mechanism of o2 transport across the cell membrane is

a. Diffusion through the lipid bilayer

b. osmosis

c. facilitated diffusion

d. diffusion via channels

e. active transport.

Why? Hydrophobic, uncharged molecule diffuses directly across

3. In an experiment, the cell interior and the extracellular solution have the same osmolality (300 mosmole/kg).

The intracellular osmolality is largely given by low-permeability (relative to water) potassium salts; the extracellular

osmolality is entirely given by urea, which has a very high permeability. What will happen to the cells volume and

why?

a. will remain unchanged because the osmolalities are equal

b. will decrease because the K salts will leave the cell

c. will increase because of the different effective osmolalities

d. will decrease because of the different effective osmolalities

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4. If the cell membrane has a very high diffusive permeability for a substance produced in the cell, then the

minimum possible intracellular concentration of the substance will be

a. negligible

b. half of the extracellular concentration

c. equal to the extracellular concentration

d. twice the extracellular concentration

Source side can never go lower than the receiving side. An example of a molecule that behaves this way is CO2.

5. The mechanisms of water transport across the cell membrane and across the capillary endothelium differ.

Which of the following defines water f low across the capillary endothelium?

The mechanisms A driving force

a. Osmosis protein concentration difference

b. osmosis Total solute concentration difference

c. bulk flow protein concentration difference

d. bulk flow total solute concentration difference

Why? Proteins cannot go across capillary endothelium, but solutes can. Also, capillary endothelium transport is

paracellular allows large amount of flow. Across a cell/plasma membrane, osmosis would be the answer.

6. Ina patient with malnutrition, measurements of alanine concentrations yielded the following results in

mmoles/liter: intestinal lumen 0.05; intestinal epithelial cells 5.2; plasma 0.4. Alanine absorption involves fluxes

from lumen to cell (across the luminal membrane) and from cell to blood (across the basolateral membrane).

From the above results, the most likely transport mechanisms are:

a. active to active

b. active to passive

c. passive to passive

d. passive to active

Why? Going up concentration gradient.

7. A patient arrives at the emergency room with severe hypernatremia (abnormally high plasma Na). His plasma

osmolality is 336 mosmoles/kg normal 280). You know that brain cells respond to extracellular hyperosmolality

by syntheisizing impermeant solutes that increase the intracellular osmolality. Assuming that this occurred in this

patient and the intracellular osmolality rose to 336, what would be the effect on the volume of the brain cells of

rapidly lowering the extracellular osmolality to 280?

a. shrinkage by 20%

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b. shrinkage by 10%

c. No change

d. Swelling by 10%

e. Swelling by 20%

How? Divide high osmolality by normal 336/280