Library · Physiology
Carbohydrate digestion
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Carbohydrates almost always reach the mouth as long chains of sugars stuck to one another, and salivary amylase, an enzyme in saliva, starts taking them apart right there.
The work continues farther down. Saliva, the pancreas, and the intestinal brush border, the ruffled inner surface of the intestinal wall, supply enzymes that break the glycosidic bonds, the links that hold the chain together. It is a long necklace cut apart until only loose beads are left. Those beads are the monosaccharides: glucose, fructose, and galactose.
The loose beads cross the wall. Glucose and galactose move into the enterocyte, the cell that lines the intestine, riding the SGLT1 cotransporter, which brings them in along with two sodium ions.
One part never comes apart: fiber, which is not digested and provides no calories. Whatever is not absorbed travels on to the colon, where it is fermented by anaerobic bacteria, the ones that live without oxygen.
In brief
Carbohydrate digestion begins in the mouth, where salivary amylase starts the breakdown.
Enzymes from saliva, the pancreas, and the intestinal brush border break the glycosidic bonds and leave monosaccharides: glucose, fructose, and galactose.
A necklace cut apart until only loose beads are left.
Glucose and galactose enter the enterocyte through the SGLT1 cotransporter, along with two sodium ions.
Fiber is not digested and provides no calories; whatever is not absorbed is fermented by anaerobic bacteria in the colon.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Carbohydrates, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Nutrient Absorption, StatPearlsPublished
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