Why doesn't the intestine digest itself?

In summary: That is exactly what can happen when proteolytic enzymes are trapped in the pancreas and starts a process of auto-digestion.
  • #1
ORF
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Hello

I have read this article about why doesn't the stomach digest itself
https://www.scientificamerican.com/article/why-dont-our-digestive-ac/

but also during the digestion along the small intestine, there are enzymes. How does the small intestine defend against these enzymes? ( I suppose that in a similar way as the stomach does ).

Thank you for your time

Regards.
 
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  • #2
That would be because digestion actually occurs mainly in the duodenum and stomach. The duodenum is covered with protective mucous and serous fluid as well as the acid being neutralised by the alkaline chemicals from the pancreas,liver and gallbladder. The intestines are used for absorption of nutrients such as proteins, carbohydrates, amino acid, sugar, fatty acid particles, vitamins, minerals, electrolytes and water with the use of villi and micro-villi.

The other reasons for enzymes not munching away on your intestine are the lock and key principle where an enzyme can only fit to a specific thing (Cells have phospholipid bilayer) and enzymes needs specific operating conditions to be active - For this reason enzymes don't work before being secreted by exocrine cells.
They have like a cap on the active part of the enzyme and In that state the enzyme is called a Proenzyme and only when its in the right condition it will remove its "Pro" cap and start breaking things down :smile:

Thats why some washing powders have to be used at specific temperatures so that the enzymes can do their thing and make your clothes clean. If you go too high with the temperature they will denature and below that they will be ineffective.
 
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  • #3
Great answer, Tracey3! I am led to wonder if pancreatic proteolytic enzymes don't also hydrolyze our digestive enzymes (including other proteolytic enzymes). That sort of activity would serve to limit the duration of digestion, at least from pancreatic enzymes.

This is interesting; the cells which line the small intestine have proteolytic enzymes on their lumenal surface which serve to hydrolyze oligo-peptides. Of course, these are fixed in place so self-digestion by these wouldn't be an issue.

From: http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/absorb_aacids.html

"The brush border of the small intestine is equipped with a family of peptidases. Like lactase and maltase, these peptidases are integral membrane proteins rather than soluble enzymes. They function to further the hydrolysis of lumenal peptides, converting them to free amino acids and very small peptides. These endproducts of digestion, formed on the surface of the enterocyte, are ready for absorption."

As Mr. Spock would say, fascinating.
 
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  • #4
MirandaSez said:
Great answer, Tracey3! I am led to wonder if pancreatic proteolytic enzymes don't also hydrolyze our digestive enzymes (including other proteolytic enzymes). That sort of activity would serve to limit the duration of digestion, at least from pancreatic enzymes.

This is interesting; the cells which line the small intestine have proteolytic enzymes on their lumenal surface which serve to hydrolyze oligo-peptides. Of course, these are fixed in place so self-digestion by these wouldn't be an issue.

I could be wrong but I remember that there is some interaction between enzymes in the boundary layer and N-terminals which are the signal peptides on the digestive enzymes. This in turn gave the signal to peptidases and proteases enzymes to start protein degradation of the digestive enzymes whereby proteolytic cleavage breaks down proteins into smaller peptides and amino acids so that they may be absorbed.
 
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  • #5
Hello

Thank you for your answers :)

Regards.
 
  • #6
Just out of interest this is part of the pathology of pancreatitis when proteolytic enzymes are trapped and activated inside the pancreas and start a process of auto-digestion.
 
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  • #7
@Laroxe : omg, that is horrible!
 

1. What prevents the intestine from digesting itself?

The intestine is lined with a protective layer of mucus that acts as a barrier between the digestive enzymes and the intestinal tissue. This mucus layer also contains bicarbonate, which helps neutralize any acidic digestive enzymes that may come into contact with the intestine.

2. Can the intestine digest itself under certain conditions?

In rare cases, such as in severe cases of inflammatory bowel disease or obstruction, the protective mucus layer may become damaged or disrupted, allowing the digestive enzymes to come into contact with the intestinal tissue. This can lead to the intestine digesting itself, a condition known as autodigestion.

3. How does the intestine prevent the breakdown of its own cells?

The intestinal cells have specialized proteins on their surface that prevent the digestive enzymes from coming into contact with them. These proteins act as a shield, protecting the cells from being digested by the enzymes.

4. What happens if the intestinal cells are damaged or lost?

The intestine has a high rate of cell turnover, meaning that damaged or lost cells are constantly being replaced by new cells. This process is regulated by stem cells located in the intestinal lining, ensuring that the intestine is always able to maintain its protective barrier.

5. Is there any risk of the intestine digesting itself during digestion?

No, the digestive enzymes are only activated in the small intestine, where food is present. The stomach and large intestine do not secrete these enzymes, so there is no risk of autodigestion in these parts of the digestive system.

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