How are polysaccharides and disaccharides digested ?

Polysaccharides and disaccharides are complex carbohydrates that are broken down into simpler sugars during the process of digestion. Here's how each of these types of carbohydrates is digested:

1. Polysaccharides: Polysaccharides are large carbohydrate molecules composed of multiple monosaccharide units linked together by glycosidic bonds. Examples include starch, glycogen, and cellulose. The digestion of polysaccharides primarily occurs in the following steps:

• Mouth: The digestion of polysaccharides begins in the mouth with the action of salivary amylase, an enzyme secreted by the salivary glands. Salivary amylase breaks down starch molecules into smaller polysaccharides, maltose (a disaccharide), and dextrins.

• Stomach: Once food enters the stomach, the acidic environment denatures salivary amylase, halting further starch digestion. Therefore, starch digestion is minimal in the stomach.

• Small Intestine: The majority of polysaccharide digestion occurs in the small intestine, specifically in the duodenum and jejunum. Pancreatic amylase, secreted by the pancreas, continues the digestion of polysaccharides by breaking down starch and glycogen into maltose, maltotriose (a trisaccharide), and dextrins.

• Brush Border Enzymes: The final stage of polysaccharide digestion occurs at the brush border of the small intestine, where enzymes known as α-glucosidases (including sucrase, maltase, and isomaltase) further break down disaccharides and trisaccharides into monosaccharides.

• Absorption: The resulting monosaccharides (such as glucose, galactose, and fructose) are absorbed across the epithelial lining of the small intestine into the bloodstream and transported to various tissues for energy or storage.

2. Disaccharides: Disaccharides are carbohydrate molecules composed of two monosaccharide units joined by a glycosidic bond. Examples include sucrose, lactose, and maltose. The digestion of disaccharides follows a similar process to polysaccharides but is simpler:

• Small Intestine: Disaccharides are primarily digested in the small intestine, specifically at the brush border membrane of enterocytes (intestinal epithelial cells). Brush border enzymes, such as sucrase, lactase, and maltase, hydrolyze disaccharides into their constituent monosaccharides.

• Hydrolysis: Sucrase breaks down sucrose into glucose and fructose, lactase breaks down lactose into glucose and galactose, and maltase breaks down maltose into two glucose molecules.

• Absorption: The resulting monosaccharides are then absorbed across the epithelial lining of the small intestine into the bloodstream and transported to various tissues for energy or storage, similar to the absorption of monosaccharides derived from polysaccharides.

In summary, both polysaccharides and disaccharides are digested into monosaccharides, which are then absorbed into the bloodstream for use by the body. The digestion of these carbohydrates involves the action of various enzymes secreted by the salivary glands, pancreas, and brush border of the small intestine.