Feedback on MCQ's in Today's CA Test
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E.S.Prakash
Oct 19, 2010, 6:36:32 AM10/19/10
to MBBS Batch 16, Medical Physiology at SOM, AIMST University
Dear Batch 16 (Year 1) Students,
I can't provide the actual MCQs that appeared in the test this afternoon but I hope you will find feedback based on content covered in the MCQs helpful.
1. Growth hormone liberated from the anterior pituitary gland stimulates the growth of skeletal muscle fibres. This is enabled by the fact that this messenger travels to muscle in the blood stream and acts on growth hormone receptors on muscle. This is an example of endocrine communication.
2. The rate of diffusion of a molecule across the cell membrane is inversely proportional to the thickness of the cell membrane. [see Fick's Law of Diffusion]
3. The maximum amount of oxygen that 1 g of Hb A can bind is 1.34 ml.
4. In an individual whose blood group is A, he/she would have the A antigen on his/her RBC membranes and anti-B antibodies in his/her plasma.
5. The mature red blood cell does not have mitochondria; thus, it respires anerobically generating ATP by glycolysis alone; i.e., RBCs do not actually consume oxygen - they simply transport it.
6. In epithelia, tight junctions constitute a barrier between content in the lumen of the epithelium and interstitial fluid (image attached).
7. The extrusion of calcium from cells via Na-Ca exchanger is an active process as the ECF Ca is higher than ICF Ca concentration. The Na ion gradient that powers it is generated by Na-K ATPase, a fundamental ATP consuming primary active transport process. Thus, the Na-Ca exchanger is an example of "secondary active transport".
8. O, Rh negative blood group is potentially a "universal donor" because these individuals do not have A, B or the Rh antigens - the three antigens that often initiate clinically significant hemolytic transfusion reactions and this is why ABO and Rh compatibility between donors and recipients is routinely checked prior to transfusion. This process is called "Grouping". A fundamental principle in transfusion is that we avoid as far as possible transfusing antigens into the recipient of the transfusion. I am being brief here but to answer the common question that individuals with O Rh negative blood have anti A and anti B antibodies in their plasma, the point is that it does not matter because antibodies in donor's plasma would get considerably diluted in recipient's plasma and are therefore very unlikely to elicit a significant transfusion reaction. In contrast, small amounts of antigens can elicit a profound immune response. "Universal donor" does not mean an individual who is O, Rh negative can donate to anyone. Whether transfusion would be compatible in a given case is further tested after ABO and Rh groups are matched using what is called "cross matching". In this procedure, recipient's plasma is crossed (mixed) with donor's red blood cells. If an agglutination reaction is observed, this implies that the recipient has antibodies to some donor RBC antigens other than the A, B and the Rh antigen, and therefore the transfusion cannot proceed.
9. This question contained correct and incorrect statements about cyclins, proteins that regulate transition from one phase of the cell cycle to the next. There are some cyclins that promote transition across restriction points and some that inhibit transition at restriction points. When there are defects in DNA synthesis, cyclins inhibit progression of the cell cycle into the M phase (this also makes logical sense and serves to minimize transmission of defective DNA to daughter cells). Loss of function mutation in p53, a tumor suppressor protein, will fail to elicit apoptosis - an inbuilt genetic program that results in cell death. As a result of failure of initiation of the apoptotic cascade, cells with mutated DNA are more likely to proliferate uncontrolled leading to formation of cancers.
10. We calculated the osmolality of 0.9% NaCl in class and it comes closest to 300 mOsm/Kg H2O. The reason we should memorize this is because this solution is isotonic with normal human plasma; in a few years time you will get to administering this solution right, left and center when you treat individuals with isotonic dehydration.
11. Since 0.9% NaCl is isotonic, administration of this solution will cause the least change in ICF volume in an individual with isotonic dehydration (who by definition has a plasma osmolality that is essentially normal - around 290-300 mOsm/Kg H2O), but of course 0.9% NaCl will serve to expand ECF volume.
12. In the steady state, ICF volume increases in hypotonic dehydration where by definition ECF becomes dilute compared to normal plasma thereby causing some water to enter cells.
13. If total body mass is 76 kg and fat mass is 15 kg, then lean body mass (fat-free mass) is 61 kg.
14. Nicotinic acetylcholine receptor is a ligand-gated ion channel that opens when two molecules of Ach (the ligand) bind to it.
15. This question asked specifically about the statement among choices provided that best described the mechanistic link between primary and secondary active transport - the answer is this: if ion gradients generated by primary active transport are disrupted, then secondary active transport processes dependent on that gradient will diminish. For example, if we inhibit Na-K ATPase, then the Na gradient across the cell membrane will diminish and the ability of the Na-Ca exchanger to extrude Ca from the cell will diminish.
All the best,
ESP
**********************
I can't provide the actual MCQs that appeared in the test this afternoon but I hope you will find feedback based on content covered in the MCQs helpful.
1. Growth hormone liberated from the anterior pituitary gland stimulates the growth of skeletal muscle fibres. This is enabled by the fact that this messenger travels to muscle in the blood stream and acts on growth hormone receptors on muscle. This is an example of endocrine communication.
2. The rate of diffusion of a molecule across the cell membrane is inversely proportional to the thickness of the cell membrane. [see Fick's Law of Diffusion]
3. The maximum amount of oxygen that 1 g of Hb A can bind is 1.34 ml.
4. In an individual whose blood group is A, he/she would have the A antigen on his/her RBC membranes and anti-B antibodies in his/her plasma.
5. The mature red blood cell does not have mitochondria; thus, it respires anerobically generating ATP by glycolysis alone; i.e., RBCs do not actually consume oxygen - they simply transport it.
6. In epithelia, tight junctions constitute a barrier between content in the lumen of the epithelium and interstitial fluid (image attached).
7. The extrusion of calcium from cells via Na-Ca exchanger is an active process as the ECF Ca is higher than ICF Ca concentration. The Na ion gradient that powers it is generated by Na-K ATPase, a fundamental ATP consuming primary active transport process. Thus, the Na-Ca exchanger is an example of "secondary active transport".
8. O, Rh negative blood group is potentially a "universal donor" because these individuals do not have A, B or the Rh antigens - the three antigens that often initiate clinically significant hemolytic transfusion reactions and this is why ABO and Rh compatibility between donors and recipients is routinely checked prior to transfusion. This process is called "Grouping". A fundamental principle in transfusion is that we avoid as far as possible transfusing antigens into the recipient of the transfusion. I am being brief here but to answer the common question that individuals with O Rh negative blood have anti A and anti B antibodies in their plasma, the point is that it does not matter because antibodies in donor's plasma would get considerably diluted in recipient's plasma and are therefore very unlikely to elicit a significant transfusion reaction. In contrast, small amounts of antigens can elicit a profound immune response. "Universal donor" does not mean an individual who is O, Rh negative can donate to anyone. Whether transfusion would be compatible in a given case is further tested after ABO and Rh groups are matched using what is called "cross matching". In this procedure, recipient's plasma is crossed (mixed) with donor's red blood cells. If an agglutination reaction is observed, this implies that the recipient has antibodies to some donor RBC antigens other than the A, B and the Rh antigen, and therefore the transfusion cannot proceed.
9. This question contained correct and incorrect statements about cyclins, proteins that regulate transition from one phase of the cell cycle to the next. There are some cyclins that promote transition across restriction points and some that inhibit transition at restriction points. When there are defects in DNA synthesis, cyclins inhibit progression of the cell cycle into the M phase (this also makes logical sense and serves to minimize transmission of defective DNA to daughter cells). Loss of function mutation in p53, a tumor suppressor protein, will fail to elicit apoptosis - an inbuilt genetic program that results in cell death. As a result of failure of initiation of the apoptotic cascade, cells with mutated DNA are more likely to proliferate uncontrolled leading to formation of cancers.
10. We calculated the osmolality of 0.9% NaCl in class and it comes closest to 300 mOsm/Kg H2O. The reason we should memorize this is because this solution is isotonic with normal human plasma; in a few years time you will get to administering this solution right, left and center when you treat individuals with isotonic dehydration.
11. Since 0.9% NaCl is isotonic, administration of this solution will cause the least change in ICF volume in an individual with isotonic dehydration (who by definition has a plasma osmolality that is essentially normal - around 290-300 mOsm/Kg H2O), but of course 0.9% NaCl will serve to expand ECF volume.
12. In the steady state, ICF volume increases in hypotonic dehydration where by definition ECF becomes dilute compared to normal plasma thereby causing some water to enter cells.
13. If total body mass is 76 kg and fat mass is 15 kg, then lean body mass (fat-free mass) is 61 kg.
14. Nicotinic acetylcholine receptor is a ligand-gated ion channel that opens when two molecules of Ach (the ligand) bind to it.
15. This question asked specifically about the statement among choices provided that best described the mechanistic link between primary and secondary active transport - the answer is this: if ion gradients generated by primary active transport are disrupted, then secondary active transport processes dependent on that gradient will diminish. For example, if we inhibit Na-K ATPase, then the Na gradient across the cell membrane will diminish and the ability of the Na-Ca exchanger to extrude Ca from the cell will diminish.
All the best,
ESP
**********************
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