Prep4USMLE Forum » USMLE Step 1 Forum » Pathology Forum |   Calcium Receptor mutation NBME F2 S2

Author	11 Posts
nadiabarati	06/10/06 - 04:57 PM             #1 22. A 3-year-old boy has a mutation in the calcium receptors on cell surfaces of his parathyroid gland and on the basolateral (blood) side of the thick ascending limb of the loop of Henle. Which of the following patterns is expected with a mutation that leads to activation of this receptor in the absence of binding of its ligand, calcium? Serum Ca2+ Parathyroid hormone Urine calcium A ) Hypercalcemia high high B ) Hypercalcemia high low C ) Hypercalcemia low high D ) Hypercalcemia low low E ) Hypocalcemia high high F ) Hypocalcemia high low G ) Hypocalcemia low high H ) Hypocalcemia low low
robin082006 Forum Hero Topics: 471 Posts: 5,123	06/10/06 - 05:00 PM             #2 B Edited by robin082006 on 06/11/06 - 09:48 AM ___________________ The Key to Succeed is Patience.
nadiabarati	06/10/06 - 05:03 PM             #3 calcium has a negative and positive feedback, depends on Ca concentration, on its receptors on parathyroid gland. What does it mean that these receptors are active in the absence of their ligand, Ca? It means PTH is constantly released and we will have increased PTH, increased Ca? In the kidney it means constant reabsorption of Ca and thus low Ca levels in the urine? So the answer is B? Thanks for any input.
hlab27 Forum Newbie Topics: 0 Posts: 16	06/10/06 - 05:12 PM             #4 Hmmm... good question. If the body thinks that there is plenty of Ca++ due to activation (that is how I am interpreting this), then there should be HYPOcalcemia, HYPERphosphatemia, LOW PTH, and LOW Ca++ in the urine. So H?
sridevibandaru24 Forum Guru Topics: 33 Posts: 434	06/11/06 - 09:33 AM             #5 Answer: G
alexaE Forum Elite Topics: 23 Posts: 334	06/11/06 - 09:45 AM             #6 no idea.F? i dont understand the question either Nadia ___________________ veni vidi...vincam
robin082006 Forum Hero Topics: 471 Posts: 5,123	06/11/06 - 09:48 AM             #7 This q has been discussed. people chose B activation of receptors in parathyroid gland--> increase in PTH--> increased Serum Ca++, decreased urinary Ca++, decreased Serum Phosphate, increased urinary phosphate. ___________________ The Key to Succeed is Patience.
cerebral Forum Newbie Topics: 6 Posts: 31	06/11/06 - 07:55 PM             #8 Ca++ decreases release of PTH so if receptors are activated even without Ca++ then PTH should logically decrease. since PTH is low serum Ca++ should be low. Basolateral membrane activation without Ca++ would give false signal of adequate Ca++ absorbtion so urinary Ca++ would likely increase, though I'm not sure about this point. I choose G. .
sridevibandaru24 Forum Guru Topics: 33 Posts: 434	06/13/06 - 07:22 AM             #9 Thats what i am exactly thinking cerebral!
Cedrick Forum Fanatic Topics: 322 Posts: 1,986	07/02/06 - 02:06 PM             #10 here it is again
star1 Forum Guru Topics: 93 Posts: 827	07/02/06 - 02:57 PM             #11 yes ................... Ca... causes negative feedback to PTH gland

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