Chemical Digestion

Chemical Digestion

1. Digestive enzymes

   • Break down substances with the addition of water at specific bonds
   • Digestive enzymes are hydrolytic enzymes
   • Have an optimum pH to function at

2. Carbohydrates

   • Salivary amylase breaks carbohydrates into maltose
     • Action stops in the stomach (too acidic)
       • Pancreatic amylase continues the hydrolysis to maltose
         • Brush border enzymes of the small intestine break down disaccharides to monosaccharides (mainly glucose)
           • Monosaccharides are absorbed by intestinal cells into blood capillaries
           • Maltose broken down by maltase
           • Lactose broken down by lactase
           • Sucrose broken down by sucrase

3. Nucleic acids

   • Pancreatic nucleases break down DNA and RNA into nucleotides
     • Brush border nucleotidases break down the nucleotides to sugar, phosphate, and nitrogenous base
       • These chemicals enter intestinal cells into the blood capillaries

4. Fats

   • First emulsified by bile in the duodenum
     • Digested by pancreatic lipase to glycerol and fatty acids
       • Enter intestinal cells where the fatty acids are packaged as lipoproteins and then enter the lacteals

5. Protiens

   • Pepsin in the stomach hydrolyzes proteins into short polypeptides
     • Three pancreatic proteinases – trypsin, chymotrypsin, and carboxypeptidase break down polypeptides to peptides and some amino acids
       • Peptidases (brush border enzymes) complete the digestion of peptides into amino acids in the small intestine
         • Amino acids are absorbed by intestinal cells into blood capillaries