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Carbohydrate Digestion And Absorption - Carbohydrate Metabolism

In this video we discuss how carbohydrates are digested and absorbed in the body. We cover the digestive enzymes that take part in the process, and the fates of the different types of carbohydrates once they are digested and absorbed. Transcript/notes A quick review, there are 3 main types of carbohydrates, monosaccharides, which are single molecules, disaccharides, which are 2 monosaccharides bonded together and polysaccharides, which are many monosaccharide molecules bonded together, and some shorter strands of polysaccharides are often called oligosaccharides. Our bodies produce and release enzymes that basically break apart larger carbohydrate molecules into smaller units. There are 2 main places that carbohydrate digestion or breakdown takes place, in the mouth and in the small intestine. In the mouth, salivary glands release salivary amylase, which is an enzyme that starts breaking down starch molecules. Starch is a polysaccharide molecule that contains a large number of glucose units bonded together and it is found in many foods including rice and potatoes. Once the food or bolus is swallowed and enters the stomach, the low pH of the stomach inactivates the salivary amylase. There is virtually no digestion of disaccharides until they get to the small intestine, and we will cover them in a minute. As the bolus moves from the stomach into the duodenum and jejunum, which are the first parts of the small intestine, the pancreas releases pancreatic juice into the small intestine. This juice contains pancreatic amylase, which is an enzyme that continues the breakdown or digestion of starch into shorter strands of glucose. The brush border or microvilli, which are tiny hair like projections located on the enterocyte cells of the small intestine also contain enzymes that finish the breakdown of starch into single glucose molecules that are ready for absorption. Now for the 2 unit disaccharides, which my cookie dough blizzard has a ton of. So, the 3 main disaccharides are sucrose or sugar, which is comprised of a glucose molecule and a fructose molecule, lactose, which is galactose and glucose, and maltose, which is 2 glucose units. The enzymes that act on these are sucrase, lactase and maltase which are also located on the brush border of the enterocyte cells. So, basically the body has broken down these carbohydrates into single glucose, fructose and galactose units. Glucose and galactose are mainly absorbed into the enterocyte cells through an SGLT1 protein transporter on the membrane of the cell. Fructose is absorbed into cells through a GLUT5 transporter. On the other side of the enterocyte cells, glucose, galactose and fructose are transported out of the cell through a GLUT2 transporter, into the portal vein where they travel to the liver. In the liver, fructose and galactose are mainly converted into glucose. The actual glucose molecules from the food can be taken up by the liver and stored as liver glycogen, or they can become part of blood glucose and be used by cells throughout the body as energy, they can also be taken up by muscle cells and stored as muscle glycogen or they can be converted into fat and stored in adipose or fat tissue. Timestamps 0:00 Intro 0:18 Carbohydrate review 0:46 Carbohydrate digestion in the mouth 1:13 Carbohydrate digestion in the small intestine 1:29 The microvilli on enterocyte cells 1:46 Simple carbohydrates and enzymes 2:13 Glucose, fructose and galactose absorption 2:33 Carbohydrates in the liver