NBME 20 Cholecalciferol (NBME Answers)

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submitted by ∗hayayah(1212)

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Notice, the stem says "precorsors in the skin"

D3 (cholecalciferol) from exposure of skin (stratum basale) to sun, ingestion of fish, milk, plants.

D2 (ergocalciferol) from ingestion of plants, fungi, yeasts.

Both converted to 25-OH D3 (storage form) in liver and to the active form 1,25-(OH)2 D3 (calcitriol) in kidney.

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sympathetikey C is the 3rd letter in the alphabet. Hence, D3 = Cholecalciferol +6

karljeon Thanks for the explanation. The question stem made it sound like "what future step will be decreased?" Actual question: "Decreased production of which... is most LIKELY TO OCCUR in this patient?" Maybe NBME needs a grammar Nazi working for them. +11

bharatpillai question says "decreased production of which of the following precursors in skin is most likely to occur in this patient? the answer has to be 7-dehydrocholecalciferol! +7

bharatpillai 7 dehydrocholesterol +3

brbwhat Yeah i did the same, but then realised acc to uw flowchart 7dehydrochole.. is converted to cholecalciferol in presence of uv rays. So the decreased precursor would be cholecalciferol since we already have 7 dehydrocholecalciferol not being converted by uvrays Tho the uw chart sites both ergo and chole as dietary sources. +6

drzed Wouldn't 7-dehydrocholesterol build up in the skin? Since UV rays convert 7-dehydrocholesterol into cholecalciferol, if you are lacking the conversion, the reactant (7-dehydrocholesterol) should accumulate. +2

brbwhat They’re asking decreased production of which of the following precursor would occur? 7 dehydrocholestrol builds up, but decreased production of cholecalciferol takes place, which is a precursor in the pathway for vitamin d formation +10