#Explanations for the 2013-2014 Official USMLE Step 1 Practice Questions

From the official 2013-14 “Step 1 Content Description and General Information” booklet. I’ve listed the correct answer for each question with a brief explanation ± take home points. I can t reproduce the questions themselves of course as they re copyrighted.

28 Comments

sdn user

06.08.14 at 9:50 am

Hi Ben,

Saw your posts on SDN and went through all of these. Very helpful so thanks!

I also don t really understand Block 2 number 48 s notorious insulinoma question. Sorry to bring it up again, read the above comment as well. I get that C-pep and Insulin are secreted together in normal circumstances, as well as in insulinoma, as opposed to factitious insulin administration (Cpeptide below 0.5 and insulin somewhere in the normal 5-20 or higher range?). But here the insulin is normal (ok i get that it can be normal in an insulinoma) but the c-pep is LOW NORMAL (0.5-2.5 is normal, it s at 0.5) shouldn t it be closer to 2.5 if it s an insulinoma? Also is Cortisol low?(10 ug/dl when normal is 0800 h: 5-23 μg/dL // 1600 h: 3-15 μg/dL 2000 h: 50% of 0800 h ). Not sure what to make of those given values, I know Cortisol varies based on ACTH which is high in the AM I believe.

Lastly, on Block 3 number 120 about the loops I was thrown about the last column water absorption in the DESCENDING loop of henle which is before the Thick ascending limb where loops work. So are we talking about the water absorption in the Descending Limb before or after steady state? Wouldn t there be increased absorption of water if we were losing a lot of water with loops?

Thanks in advance!

Ben

06.08.14 at 8:21 pm

Glad they ve been helpful.

48) You would think C-peptide should be equivalent to insulin (high-normal and high-normal), but lab tests actually aren t that magically reliable. Too many factors at play in a real live physiological patient. For one, the half-lives of the two are different. I agree that the labs here aren t particularly suggestive of an insulinoma (if it were a factitious disorder vs insulinoma question, they would be obvious). This question is only asking where do tumors that cause hypoglycemia live.

120) This is how the countercurrent exchange mechanism works. Ions are pumped into the medullary interstitium in the ascending loop, but the increased osmolarity then causes increased water absorption in the descending loop, allowing for the creation of increasingly concentrated filtrate. Resorption of water in the limb depends on having a hyperosmotic medullary interstitium, which is created via the triporter. With lasix, you do have increased free water absorption distally in the collecting ducts, but this compensation is not able to keep up with the solute tide and thus diuresis ensues.