Carbohydrate Digestion & Absorption

Overview and Carbohydrate Types00:00:00

Dr. Mike introduces the process of carbohydrate digestion and absorption. The major ingested carbohydrates are starch, glycogen, and cellulose, which are polymers that must be broken down into monosaccharides (glucose, galactose, and fructose) for absorption.

Chemical Structure and Oral Digestion00:03:01

Explanation of alpha 1-4 glycosidic bonds in starch and glycogen versus beta 1-4 bonds in cellulose. Since humans lack enzymes to break beta bonds, cellulose acts as fiber. Salivary amylase begins breaking alpha 1-4 bonds in the oral cavity.

Small Intestine and Pancreatic Enzymes00:09:47

As chyme enters the duodenum, CCK triggers the pancreas to release more potent alpha-amylase. This further breaks down polysaccharides into disaccharides and trisaccharides like maltose, maltotriose, sucrose, and lactose.

Brush Border Enzymes00:14:26

The brush border cells of the small intestine release specific enzymes (maltase, sucrase, lactase, and alpha-dextrinase) to break down disaccharides into their final monosaccharide components.

Absorption and Transport00:16:46

Detailed explanation of transport mechanisms: glucose and galactose use SGLT (secondary active transport with sodium), while fructose enters via GLUT5. All three eventually exit the enterocyte into the bloodstream via GLUT2 transporters, traveling to the liver.