Why is small intestinal lumen alkaline?

[Monkeymaniac]

1) I did some research on my own, but I couldn't find out how relatively alkaline lumen of SI would help further digest the chyme flown down from stomach. Shouldn't acidic enviroment (ph~=2) like that of stomach be better in breaking down food particles? Or is it the alkaline environment of SI that activates digestive enzymes on the brush border (microvilli)?

2) So the digestive enzymes that are produced in pancreas and sent to SI, like trypsin, pancreatinc amylase, lipase, etc., are they fixed on the surface of the brush border, or do they actually penetrace into the brush borders and reside inside them?

Thanks in advance!

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[dingyibvs]

The digestive enzymes are mixed in with the chyme, they're not fixed to anything. They're only responsible for breaking up the food molecules, and the microvilli would then absorb them.

 

[FutureInternist]

1) I did some research on my own, but I couldn't find out how relatively alkaline lumen of SI would help further digest the chyme flown down from stomach. Shouldn't acidic enviroment (ph~=2) like that of stomach be better in breaking down food particles? Or is it the alkaline environment of SI that activates digestive enzymes on the brush border (microvilli)?

2) So the digestive enzymes that are produced in pancreas and sent to SI, like trypsin, pancreatinc amylase, lipase, etc., are they fixed on the surface of the brush border, or do they actually penetrace into the brush borders and reside inside them?

Thanks in advance!

Stuff like trypsin, pepsin etc...i.e. enzymes that are used in the initial steps of digestion are free floating but the terminal step enzymes (maltase, lactase etc) are anchored to the SI, right next to the channel that will accept the product of the terminal steps (2 glucoses or glucose + galactose in above mentioned enzymes). This way you don't have the final degradation products free floating in chyme & your body having to lasso them back in somehow.

 

[RogueUnicorn]

1) I did some research on my own, but I couldn't find out how relatively alkaline lumen of SI would help further digest the chyme flown down from stomach. Shouldn't acidic enviroment (ph~=2) like that of stomach be better in breaking down food particles? Or is it the alkaline environment of SI that activates digestive enzymes on the brush border (microvilli)?

2) So the digestive enzymes that are produced in pancreas and sent to SI, like trypsin, pancreatinc amylase, lipase, etc., are they fixed on the surface of the brush border, or do they actually penetrace into the brush borders and reside inside them?

Thanks in advance!

acidic pH inactivates pancreatic enzymes. the stomach pH is primarily maintained that low as an antimicrobial barrier, not necessarily to be function in a signficant way in digestion.

as mentioned, some enzymes are fixed on the brush border; the pancreatic secreted enzymes are free floating

 

[Monkeymaniac]

Thank you guys, I appreciate it!

 

[addo]

Bicarbonate which neutralizes gastric acid is released by the pancreas into the duodenum.