Digestion

• Primary functions

  • Prehension
  • Masticaction
  • Digestion
  • chemical
  • mammalian enzymatical
  • microbial enzymatic (fermentation)
  • Absorption
  • Elimination
• Most organic food components are too large to be absorbed
• Mastication (chewing)

  • Particle size reduction
  • Mixing with saliva
  • Initiate some digestion
• Muscular contractions


  Moves and mixes food in stomach
• Movement of intestinal contents

  • Peristaltic waves
  • Contractions, overall control of autonomic nervous system
• Different types of intestinal wall movements

  • Transport materials along the tract
  • Mix digestive juices with feed
  • Bring digestive nutrients into closer contact with intestinal mucous membrane
• Chemical action

  • Acid secretion
  • Stomach - low pH
  • Several functions
  • Low pH causes protein denaturation
  • Assists access for enzymes
  • Killing pathogen
  • Impact on enzymes (eg activation, release)
  • If food doesn’t have low enough pH or isn’t acidic enough food won’t move to intestines, chemical action can regulate the outflow
• Mammalian enzymatic action 


  Enzyme in mucous (in saliva, gastric and intestinal mucosa and pancreas) which mixes with the food to break it down (hydrolysis). Enzyme secretion controlled by hormones and nutrient supply
• Hydrolysis of peptide linkages

  • Enzymes sometimes excreted in pre-cursor forms
  • eg pepsinogen as pre-cursor for pepsin

  Hydrolysis of peptide linkages

  
• Hydrolysis of glycoside linkages

  • some ß-enzymes are produced
  • not equipped to digested ß-linkages in cellulose

  Hydrolysis of glycoside linkages

  
• Hydrolysis of ester linkages