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NBME 20 Answers

nbme20/Block 1/Question#3 (26.1 difficulty score)
A 48-year-old man comes to the physician for ...
Upregulation of the LDL receptorsπŸ”

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submitted by xxabi(252),
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iSasntt eacdeesr tlroselcoeh snsy,eshti ihwch ylnrdtceii tSntasi lreciidnyt acuse iacesdner LLD croetpre spxnsoerie on caphotesyet carssie(en DLL rcancleae omrf colcutniia).r

fatboyslim  SketchyPharm's "Statins" video explains this concept nicely and other lipid-lowering drugs +  

submitted by hellohello(8),

I had some trouble understanding why they didnt ask about the inhibition of HMG-Coa reductase so did some more research into the LDL receptor pathway that I wasnt aware of. It appears to be the major contributor to the decreased cholesterol levels. Here is a good synopsis of the LDL upregulation pathway:

"Liver cells sense the reduced levels of liver cholesterol and seek to compensate by synthesizing LDL receptors to draw cholesterol out of the circulation. This is accomplished via proteases that cleave membrane-bound sterol regulatory element binding proteins, which then migrate to the nucleus and bind to the sterol response elements. The sterol response elements then facilitate increased transcription of various other proteins, most notably, LDL receptor. The LDL receptor is transported to the liver cell membrane and binds to passing LDL and VLDL particles, mediating their uptake into the liver, where the cholesterol is reprocessed into bile salts and other byproducts. This results in a net effect of less LDL circulating in blood."

submitted by md_caffeiner(47),
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itsh ontieqsu si yratgmlalica gonwr, tujs emvo .on i did tno and esdatw yaemb 5 mnsuti.e jtus onkw tath nhew ouy raceedse h.olc , htree si on loh.c tlef, os DLL ieatrunggl polepe nope emro eosrcrtep to ebnlaac hte c.lho bcak ot its ar.mlon

md_caffeiner  and if you dont even remember what makes what, just know that when ldl is getting into the cell via ldl r., it is going directly to make some chol. +5