Calcium Receptor mutation NBME F2 S2

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Calcium Receptor mutation NBME F2 S2

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32 Posts

doc007
Forum Junior

Topics: 5
Posts: 12

03/27/06 - 03:43 PM

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

huzefa
Forum Junior

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Posts: 66

03/27/06 - 04:21 PM

I think it's G.

Low PTH, hypocalcemia and increased urinary calcium.

doc007
Forum Junior

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Posts: 12

03/27/06 - 04:51 PM

thanku huzefa!
could you please reason the answer..

doc007
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03/27/06 - 04:57 PM

34. A 58-year-old man comes to the physician because of blood in his urine. He had a nephrectomy 10 years ago because of injuries sustained in a motor vehicle collision. Evaluation shows renal cell carcinoma in his remaining kidney and pulmonary metastases. Interleukin-2 (IL-2) therapy is started. Three weeks later, CT scan confirms regression of the tumor. Which of the following most likely caused the regression?

A) An effect of IL-2 on tumor vascularization

B) Cytotoxic effects of IL-2 on tumor cells

C) Increased natural killer cell activity

D) Induction of antitumor antibodies by IL-2

E) Induction of B-lymphocyte proliferation

F) Spontaneous remission

doc007
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03/27/06 - 05:07 PM

4. A 27-year-old man is found to have a solitary thyroid nodule during a routine health maintenance examination. A thyroid scintiscan shows uptake of radioactive iodine by the nodule. Which of the following is the most likely diagnosis?

A) Chronic autoimmune (Hashimoto's) thyroiditis

B) Follicular adenoma

C) Granulomatous thyroiditis

D) Medullary carcinoma

E) Papillary carcinoma

doc007
Forum Junior

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Posts: 12

03/27/06 - 05:32 PM

18. A neonate with swelling of the neck has a decreased serum thyroxine (T4) concentration and an increased serum thyroid-stimulating hormone concentration. Which of the following agents chronically ingested by the mother during the pregnancy is the most likely cause of these findings?

A) Corticosteroids

B) Propranolol

C) Propylthiouracil

D) Thyroxine (T4)

E) Triiodothyronine (T3)

huzefa
Forum Junior

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Posts: 66

03/27/06 - 08:31 PM

22) G; because activation of the Ca2+ receptors on the Parathyroid gland will make the gland think that there is too much Ca2+ (negative feedback) and cause decrease in PTH secretion. Decrease in PTH secretion will therefore lead to Hypocalcemia. Activation of the Ca2+ receptor on the basolateral side of the TAL will result in hypocalcemia and increased urinary calcium.

robin082006
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03/28/06 - 12:33 AM

22.G

34.C

4. B

18. E

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hrishi
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03/28/06 - 05:02 AM

ans to 18 why not c?

meroon
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Posts: 52

03/28/06 - 12:29 PM

#10

Ans to 18 is not propylthiouracil because it is used in pregnancy to treat thyrotoxicosis as it is strongly protien bound and therefore crosses the placenta less readily.And the defenitive management is delayed till delivery.

meroon
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03/28/06 - 12:30 PM

#11

But i am confused between T4 and T3.

linaorvos
Forum Elite

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Posts: 258

03/30/06 - 06:54 AM

#12

Isn't congenital Hypothyr, due to maternal exposure to excess iodine, antithyroid medications or exposure of the infant to maternal antithyroid antibodies. what about C.??

yasmeen
Forum Guru

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Posts: 942

03/30/06 - 07:24 AM

#13

MATERNAL INGESTION OF ANTITHYROIDS DO LEAD TO FETAL HYPOTHYROIDISM SO I THINK ITS C

yasmeen
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03/30/06 - 07:25 AM

#14

REST I AGREEWITH ROBIN

robin082006
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03/30/06 - 08:58 AM

#15

I searched Goljan and go with E for q 18 now, thank you for your idea.

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robin082006
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03/30/06 - 08:58 AM

#16

ABout this q anyone thinks about choice B?

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

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linaorvos
Forum Elite

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Posts: 258

03/30/06 - 09:16 AM

#17

Robin, you answer for 18 was E at the begining raised eyebrow

I also think it's B, activation of PTH R. leads to HyperCa, inc PTH, inc Kidney reabsorp of Ca in DCT.

yasmeen
Forum Guru

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Posts: 942

03/30/06 - 10:19 AM

#18

i also think its Q 22 IS B

meroon
Forum Senior

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Posts: 52

03/30/06 - 05:29 PM

#19

Activation of Ca receptor should send signal to the cell to decrease the production and release of PTH.HERE instead of the normal ligand its a mutation that activates the receptor.so irrespective of Ca level, cell is going to release low PTH.THIS leads to hypocalcemia.

I searched for a Ca receptor in the thick ALH.I couldnt find one.AND it is said that Ca is absorbed paracellularly here owing to presence of k+ ions that diffuses into lumen from interstitium.so based i cannot find an explanation.

vamsi2004
Forum Elite

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Posts: 144

08/04/06 - 07:25 PM

#20

22- Bor G

18- propyl thio uracil- right?

proctalgia
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08/04/06 - 08:10 PM

#21

I am confused. Ref Q 18.
What Effect will increased maternal T3 have on fetal thyroid gland development??
Please explain. shaking head

Dragonfly
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Topics: 27
Posts: 338

08/06/06 - 11:10 AM

#22

22. B. it is a simple Negative feedback concept. when Ca can not bind to its R on PT, the gland thinks that there is a state of HypoCa (which is not true) and secrets more PTH i the hope of getting Ca up which is already up !! as a result you have Hypercalcemia with high PTH and hypocalciuria (inc. PTH-dep and Vit-D dep reabsorption frfom kidneys)
although i am not sure of the importance of the basolateral (blood) side Ca-Rs. does anyone have any idea?

18.c. i think like yesmen this is the only possibility. according to Katzung , even though PTU is not belived to cross the placenta as good as Metimazol. it is not recommended to pregnants as it may cause hypothyroidism.

Rest i agree with robin smiling face

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mitty
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08/21/06 - 08:46 PM

#23

For q 22 I think the answer is E.My explanation is since their is mutuation of the PTH hormone receptor on the PTH gland there will not be negative feed back so their will be increase of PTH.And b/c their is no ca receptor in the ascending limb of Henle the effect of the PTH hormone for calicum reabsorption is absent so there will be hypocalcemia and high calcium in urine.

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tn1kinobe
Forum Newbie

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Posts: 21

09/14/06 - 12:31 AM

#24

robin082006 wrote:
I searched Goljan and go with E for q 18 now, thank you for your idea.

Robin is right you guys.. PTU DOES NOT CROSS THE PLACENTA. T3 is the more active form compared to T4. Choose T3.

dc1
Forum Newbie

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Posts: 8

09/15/06 - 01:05 PM

#25

doc007 what are the answers??????\

22 g,18 c ,34-c,4 b??can anyone explain?

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