NBME 24 Intestinal mucosa (NBME Answers)

Retired NBME 24 Answers

nbme24/Block 2/Question#48 (reveal difficulty score)
The breakdown of dipeptides and tripeptides ...
Intestinal mucosa 🔍 / 📺 / 🌳 / 📖
tags: GI

+381 upvote downvote
submitted by ∗seagull(1933)

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The semantics of this question made me vomit blood.

One day a patient will look me in the eyes and ask, "Where are tripetides broken down?" I will smile at them and say, "the intestinal mucosa and not the duodenum." They'll smile back and I'll walk away and think of this moment as I jump from the window.

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sympathetikey Too real. +5

mcl how do i upvote multiple times +22

trichotillomaniac I made an account solely so I could upvote this. +40

dragon3 ty for the chuckle +8

cinnapie @trichotillomaniac Same +5

thedeadly96 XD made my day! +2

hardly43 RIP legend @seagull +2

seagull A legend never die +4

+56 upvote downvote
submitted by ∗drdoom(1206)

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The duodenal lumen (and pancreatic proteases like CHYMOTRYPSIN) is the site where pancreatic enzymes (“endopeptidases”) cleave large polypeptides into smaller bits (=dipeptides,tripeptides). It is at the BRUSH BORDER where the smallest kinds of peptides (dipeptides,tripeptides) are broken down into their amino acids, which finally can be co-transported with Na+ into the intestinal cell.

I think about it this way:

stomach acid denatures and “opens up” proteins (without specific cleavage);
pancreatic enzymes then cleave denatured polypeptides into smaller bits;
brush border enzymes finally break down tiniest peptides into absorbable amino acids.

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regularstudent Isn't the brush border still part of the intestinal lumen? Don't the amino acids enter into the intestinal cell (the "intestinal mucosa")? +1

drdoom @regularstudent No, the lumen is literally the cavity—the empty space. +2

jj375 Still annoyed about this question, but here is a schematic in case it helps anyone else: https://doctorlib.info/physiology/medical/medical.files/image1890.jpg +2

drdoom @jj375 best schematic i’ve seen so far. superb. +2

+4 upvote downvote
submitted by ∗am4140(8)

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One of the Doctors in Training videos talked about absorption of nutrients, and specifically mentioned that dipeptides and tripeptides are cotransported with hydrogen into the Intestinal mucosal cells while single AAs are cotransported with Na+. So not only do dipeptides and tripeptides make it into the intestinal mucosa before being broken down, they actually get in faster than single AAs do.

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weirdmed51 Kudos! To you +1

+2 upvote downvote
submitted by ∗nerdstewiegriffin(45)

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Me: I am sorry to say but because of the consequences of your DM we will have to amputate your leg Patient: okay, but I have one question Me: yes? Patient: is fructose broken down in intestinal lumen or intestinal mucosa? Me: ..... Patient: ..... Me: I think its intestinal lumen

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+1 upvote downvote
submitted by ∗weirdmed51(30)

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This question broke me more than the peptides.

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+1 upvote downvote
submitted by ∗medstruggle(21)

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Why is duodenal lumen incorrect? I thought pancreatic enzymes (chymotrypsin, carboxypeptidase) would be located here.

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colonelred_ Enterokinase actives trypsinogen and is located closer to the intestinal mucosal (“brush border”). +2

drdoom Yeah, @colonelred is right. @medstruggle: the duodenal lumen (and the pancreatic /proteases/ you mention) is the site where pancreatic enzymes (“endopeptidases”) cleave large polypeptides into smaller bits. It is at the BRUSH BORDER where the smallest kinds of peptides (dipeptides, tripeptides) are broken down into their amino acids, which finally can be co-transported with Na+ into the intestinal cell. I think about it this way: stomach acid denatures and “opens up” proteins (without any specific cleavage); pancreatic enzymes then cleave denatured polypeptides into smaller bits; brush border enzymes finally break down tiny peptides into absorbable amino acids. +4

welpdedelp http://1.bp.blogspot.com/-UDdBiBiEgec/UzM61mV4pTI/AAAAAAAABRA/_qCG05fliGk/s1600/VBN.PNG +35

drdoom Nice schematic, @welpdedelp +1

drdoom ^ linkifying @welpdedelp http://1.bp.blogspot.com/-UDdBiBiEgec/UzM61mV4pTI/AAAAAAAABRA/_qCG05fliGk/s1600/VBN.PNG +4

asmamohammadi https://www.youtube.com/watch?v=HL7-fYBtJ1Y +1

+0 upvote downvote
submitted by xs34_23(0)

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theres a zanki card in the GI deck from costanzo showing luminal side H+/dipeptide and H+/tripeptide co-transporters. Then inside the intestinal mucosa, the di and tripeptides are broken down into amino acids where a basal side transporter puts them into the blood stream

Heres a link showing that:

https://lh3.googleusercontent.com/proxy/lN4Yj1xGREIoZvwwToWbxbnRl3LJbyKcglErEzHYDi6-E_syymDAE_ASibm7AL0w_syCuZg4e3NNU66tz-z6nYrowCrT1KD0LulgNb7RRQcd6jwQx4J6pVJJ1UKB

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+0 upvote downvote
submitted by ∗jbrito718(48)

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Di- and Tri- peptides can enter into enterocytes via PepT1 transporters and be broken down to amino acids within the enterocytes. Hence why the lumen is not the best answer

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-1 upvote downvote
submitted by ∗seagull(1933)

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The semantics of this question made me vomit blood.

At least one day a patient will look me in the eyes and ask " where are tripetides broken down at". I will smile at them and say "the intestinal mucosa and not the duodenum". They'll smile back and then i'll then i'll walk away and think of this moment as I jump from the window.

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weirdmed51 You got 331 vote for this dear, need more? +1

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