mechanical and chemical digestion

• what are the 2 categories of digestion?

  mechanical and chemical.
• what is mechanical digestion?


  the physical breakdown of foods through chewing by the teeth and churning by the stomach muscles.
• what is the idea behind mechanical digestion?


  the idea is to break down the food into smaller pieces that are easier to digest chemically because of the increased surface area this creates.
• what is chemical digestion?

  where secretions, like enzymes and acids, are introduced to the food along the gastrointestinal tract. Starts at the mouth and more enzymes are added by the stomach, pancreas and small intestine.
• how do digestive enzymes work?


  they usually have a single molecule as their target and they all work by hydrolysing the larger molecules into smaller molecules that can be more easily absorbed at the ileum.
• what are the 3 important groups of digestive enzymes?


  carbohydrases, lipases and proteases.
• what do cabohydrases do?

  carbohydrates --> monosaccharides.
• what does lipase do?


  lipids --> glycerol and fatty acids
• what does protease do?


  proteins --> amino acids
• what are carbohydrates and polysaccharides broken down by?


  broken down by carbohydrases
• what does carbohydrase break carbohydrates and polysaccharides down into?


  monosaccharides.
• what is the breakdown of a complex carbohydrate normally like?

  normally a multi step process with different enzymes involved, each taking it in turns to remove the next monosaccharide or the next smaller piece.
• what is starch like?


  a long chain of alpha-glucose molecules.
• what is often crucial in chemical digestion of larger biological molecules

  the breaking down by the specific set of enzymes occurs in a particular sequence.
• what is the 1st step of breaking down starch?

  salivary amylase secreted by the mouth's salivary glands. Salivary amylase begins to breakdown the starch molecules into smaller maltose molecules.
• what is the 2nd step of breaking down starch?


  on entering the stomach, the acidity of the digestive acids denatures the amylase and stops hydrolysis of starch.
• what is the 3rd step of breaking down starch?


  when food reaches the small intestine, pancreatic juice mixes with the food. The pancreatic juice comes from secretions from the pancreas. In the pancreatic juice mixture is pancreatic amylase, this restarts hydrolysis of starch into maltose.
• what is the 4th step of breaking down starch?


  the muscles of the intestine continues to push the food mixture through the ileum, maltase is introduced after being produced in the epithelial cells. Maltose is never released into the lumen of the ileum as it remains part of the absorption surface.
• what is the role of maltase?


  to breakdown the maltose formed by the amylase earlier, into component monosaccharides of alpha glucose.