Why doesn't the intestine digest itself?

[ORF]

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.

 

[Tracey3]

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

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.

 

[MirandaSez]

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.

 

[Tracey3]

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.

 

[ORF]

Hello

Thank you for your answers :)

Regards.

 

[Laroxe]

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.

 

[ORF]

@Laroxe : omg, that is horrible!