PASSIVE TRANSPORT
| A | Particle’s concentration difference across the membrane | |
| B |
Thickness of the Membrane |
|
| C |
Area of the membrane |
|
| D |
Temperature of the solution |
According to Fick’s law of diffusion, particle flux will decrease if there is an increase in the:
| A |
Particle’s concentration difference across the membrane |
|
| B |
Thickness of the Membrane |
|
| C |
Area of the membrane |
|
| D |
Temperature of the solution |
Urea is transported in the renal tubules by the following mechanism:
| A |
Active transport |
|
| B |
Passive transport |
|
| C |
Facilitated diffusion |
|
| D |
Both A and B |
Which of the following does not affect rate of diffusion?
| A |
Area of diffusion |
|
| B |
Concentration gradient |
|
| C |
Time |
|
| D |
None of the above |
The magnitude of the diffusing tendency from one region to another is directly proportionate to the cross-sectional area across which diffusion is taking place and the concentration gradient, or chemical gradient, which is the difference in concentration of the diffusing substance divided by the thickness of the boundary (Fick’s law of diffusion).
Ref:Ganong’s Review of Medical Physiology 23rd edition, Chapter 1.
Fick’s law is associated with which of the following functions?
| A |
Osmosis |
|
| B |
Phagocytosis |
|
| C |
Diffusion |
|
| D |
None of the above |
Through which of the following means of transport is folic acid absorbed in proximal jejunum?
| A |
Facilitated diffusion |
|
| B |
Active transport |
|
| C |
Passive transport |
|
| D |
Both active and passive transport |
Folic acid is absorbed in the proximal jejunum through both active and passive transport. First step in the absorption of folate involves hydrolysis of pteroyl polyglutamates into pteroyl monoglutamate by conjugase enzyme located in the intestinal mucosa. Next step involves absorption of pteroyl monoglutamate through active carrier mediated transport. Besides this, pharmacologic doses of folate are also absorbed passively by facilitated diffusion.
- After absorption from the lumen into the enterocyte intracellular enzymes reduce and methylate the monoglutamate to produce metabolically active form of folic acid. This form is then absorbed into circulation by simple diffusion.
- Most of the vitamins are absorbed passively. Cyanocobalamin is the only vitamin that that depends on active transport for its absorption. Folic acid and thiamine are the only other vitamins for which active mechanism of absorption is known.
