Physiology of Digestive System

• Intestinal digestion


  Most important part of the digestive tract. Carries out all digestive activities, namely enzymic digestion, physical digestion and absorption.
• Small intestine


  • Divided histologically into duodenum, jejunum, ileum.
• Intestinal digestion


  1. Enzymic digestion

  2. Physical digestion

  3. Absorption
• Bile


  Thick, green secretion from the liver. Stored in the gall bladder (except horse, rat, pigeon). Contains inorganic ions, bile salts, bile pigments, lipids.
• Function of bile


  Emulsification of fat globules to smaller droplets, increasing the surface area for lipase action.
• Enzymes in pancreatic juice

  • Trypsin/chymotrypsin
  • Lipase
• Enzymes in intestinal juice (succus entericus)

  • Maltase
  • Lactase
  • Sucrase
  • Lipase
  • Peptidase
• Carbohydrate & simple sugar transport & absorption

  1. Na+-coupled substrate

  2. Substrates leave the cell via facilitated diffusion
• Amino acids transport & absorption

  1. Na+-coupled substrate

  2. Substrates leave the cell via facilitated diffusion
• The pancreas secretes pancreatic juice containing carbohydrases, proteases and lipase enzymes.
• Intestinal juice from the small intestinal wall contains maltase, sucrase, lactase, peptidase, lipase.
• Absorption of end-products of digestion is aided by increased surface area of villi.
• Na+-coupled substrate (active transport)


  A type of active transport that requires the use of a transport protein and the input of energy (in the form of ATP) to move the substrate against its concentration gradient from an area of low concentration to an area of high concentration. The transport of the substrate is coupled with the movement of sodium ions (Na+) down their electrochemical gradient, which provides the energy needed for the transport.
• Facilitated diffusion


  A type of passive transport that uses a transport protein to help move a substrate down its concentration gradient, from an area of high concentration to an area of low concentration. Unlike active transport, facilitated diffusion does not require the input of energy.