Digestion FL Kap question

[SaintJude]

---

Members don't see this ad.

Pseudo-discrete. There is nothing in the passage that suggests the answer.

According to the passage, the catabolism of amino acids produces ammonia. Therefore, after a protein-rich meal, would you expect a build-up of ammonia in the lumen of the small intestine?


Yes, because the ammonia will not be able to diffuse into the intestinal epithelium.


Yes, because the rate at which digestive enzymes degrade ammonia is slower than the rate at which ammonia is produced.


No, because the ammonia will diffuse into the intestinal epithelium and will be excreted by the kidneys.


No, because the ammonia is produced inside individual cells, not within the lumen of the small intestine.

 

[pfaction]

LUMEN of small intestine = outside world! I would say no, because catabolism occurs inside the cells. Last option?

 

[ozzi22]

No, because the ammonia is produced inside individual cells, not within the lumen of the small intestine.

 

[ckramer1225]

The answer should be No ammonia is produced in individual cells. Ammonia is produced throughout the body but most of it is used by the liver to produce urea. This is assuming I still recall appropriately my Metabolism class information.

 

[SaintJude]

Yes, it's D. I did not know that ammonia is produced throughout the body in individual cells. That doesn't make sense to me. I thought digestion begins in the stomach and then continues into the intestine.

And pfaction, how did your quote below steer you to the correct answer?

LUMEN of small intestine = outside world!

 

[pfaction]

Lumens are things that are exposed to the external environment. I remembered via the other discussion of MedPR's topic that proteases usually clip on the C=O part of the amino acids, meaning that it becomes NH3+-alphaC-COOH.

Lumenal brush border peptidases similarly work to create mono amino acids, which are used via 2ndary active transport (Na, just like glucose) to enter the cell. From there, de-amination occurs to make a precursor to glucose, the ammonia (NH3) is sent to the liver to become urea.

The only possible answers are A and D. C don't work because NH3 is way too polar to diffuse through IMO.

I separate digestion and metabolism. Digestion is physical break down, metabolism is chemical break down. Peptides are digested externally and metabolized internally. Peptides, fats, glucose.

 

[SaintJude]

Ok, yes thank you for spelling out the distinction between digestion and metabolism. I didn't make a distinction between where proteins were digested (in the stomach) and metabolized. So catabolism = digestion and metabolism?

 

[pfaction]

I mean, I could be wrong on the digestion vs metabolism part. So hopefully someone either confirms or corrects me. But the rest are right.

 

[dmf2682]

I mean, I could be wrong on the digestion vs metabolism part. So hopefully someone either confirms or corrects me. But the rest are right.

Sort of right. I think digestion includes chemical breakdown but doesn't break down stuff as much. Because salivary amylase breaks down complex carbohydrates as early as the mouth.

 

[pfaction]

Right, but that's not a chemical breakdown, that's a physical breakdown. That's separating a polymer into individual components, just like how bile acids emulsify fats into smaller micelles. It's kind of like taking a hammer to concrete: you're not changing the fact its concrete, just the size of it. A chemical breakdown of concrete would make it into a separate entity thing. Once again I am usually wrong about these things, but I figured I'd help you separate the two processes. Ammonia can only come from the breakdown of amino acids, and that usually doesn't occur in the stomach, because amino acids whole are absorbed via the 2ndary Na transport.

 

[SaintJude]

Pfaction, have more faith in yourself! You got the question right!!

But, I know understand after reviewing the process. Dipeptides are broken down into single amino acids in the small intestine via digestive enzymes like dipeptidases. The single amino acids are then actively transported by the epithelial lining of the small intestine. From the blood stream, the single amino acids will then enter into individual cells for protein formation or enter the liver for catabolism. It is only then in the liver, where amino acids are broken down via deamination to release ammonia.

BUT lumen = inside space of a tubular structure,

It is the epithelial lining that can line both outside (skin) and inside of structures

Thank you for explaining!