 In this video I will describe the digestion and absorption of carbohydrates, list the major digestive enzymes which digestive or accessory organs produce each enzyme, the substrate that enzyme works on, and the products produced by that enzyme. So the enzymes we will cover are salivary amylase, pancreatic amylase, and the brush border enzymes. The chemical digestion of carbohydrates begins in the oral cavity where the enzyme salivary amylase, which is produced by the salivary glands and secreted with saliva, mixes with a bolus of food. Salivary amylase catalyzes hydrolysis of polysaccharides like starch and glycogen, producing the disaccharide maltose and short branched polysaccharides known as limit dextrins. While salivary amylase initiates this process in the oral cavity, following deglutition, the low pH of gastric juice causes denaturation of the salivary amylase, pancreatic juice contains pancreatic amylase that will complete the chemical digestion of starch and glycogen to produce maltose and limit dextrins. The other disaccharides shown in the image here, sucrose and lactose come directly from the diet. Sucrose is table sugar, which is also found in some fruits, and lactose is milk sugar. The chemical digestion of carbohydrates is completed within the duodenum, where there are brush border enzymes. The term brush border refers to the microvilli on the apical surface of enterocytes. These are the epithelial cells forming the inner lining of the intestines, so the microvilli create a large surface area on the apical surface of the enterocytes. This large surface area enables a efficient mechanism of chemical digestion and then subsequent nutrient absorption. The brush border, the plasma membrane of the microvilli, has enzymes that are embedded in it. These are the brush border enzymes, and brush border enzymes are responsible for the final step in the chemical digestion of carbohydrates. So a dextrinase is the brush border enzyme that catalyzes hydrolysis of limit dextrins to produce glucose, maltase is the brush border enzyme that catalyzes hydrolysis of maltose to produce two glucose molecules from every maltose, sucrase is the brush border enzyme that catalyzes hydrolysis of sucrose producing one molecule of glucose and one molecule of fructose, and lactase is the brush border enzyme that catalyzes the hydrolysis of lactose producing one glucose molecule and one galactose molecule. Carbohydrates are absorbed in the form of monosaccharides, so glucose is the primary monosaccharide that's absorbed from the diet and glucose enters enterocytes through a mechanism of secondary active transport. The sodium glucose linked transporters are cotransporter proteins that enable glucose to enter the enterocyte as sodium also enters through the SGLT protein, sodium is moving down its concentration gradient into the enterocyte and this movement of sodium drives the transport of glucose. The low concentration of sodium inside of the enterocyte is maintained by the sodium potassium pump the sodium potassium ETPase that uses primary active transport to drive sodium out of the cell and potassium into the cell, so after glucose is transported into the enterocyte through the SGLT protein by secondary active transport glucose then exits the basolateral surface of the enterocyte by facilitated diffusion through a GLUT protein also known as an SLC solute carrier protein. The GLUT proteins enable facilitated diffusion of glucose, but GLUT proteins also enable facilitated diffusion of a wide variety of other water soluble nutrients including the other monosaccharides shown in this illustration galactose and fructose. So while galactose enters the apical surface through an SGLT protein using a secondary active transport similar to glucose we can see here that fructose can enter the apical surface by facilitated diffusion through a GLUT protein and then all of the monosaccharides exit the enterocyte by facilitated diffusion and then enter the bloodstream.