Oral Digestion

• Digestion


  The process of breaking down food into smaller components that can be absorbed and used by the body
• Digestive physiology


  • Understand the processes of digestion
  • Understand chemical and mechanical processes
  • Recognize different types of digestive tracts
  • Describe control (nervous and hormonal) of digestion
• Topics


  • Introduction
  • Oral digestion
  • Gastric digestion
  • Intestinal digestion
  • Gastrointestinal motility
  • Ruminant digestion
  • Avian digestion
• Digestion


  1. Ingestion

  2. Digestion

  3. Absorption
• Ingestion


  1. Prehension

  2. Mastication

  3. Deglutition
• Monogastric animals


  Animals with a single-chambered stomach (e.g. humans, dogs, cats)
• Polygastric animals


  Animals with a multi-chambered stomach (e.g. ruminants like cows, sheep)
• Oral digestion


  • Very little digestion in the mouth
  • Salivary glands produce mucus and amylase enzyme in monogastric animals, but no amylase in ruminant saliva
  • Amylase converts starch to maltose and dextrins
  • Motility is voluntary, namely mastication
  • Food transformed into bolus before swallowed (deglutition)
  • Bolus transferred along the oesophagus by peristalsis and gravity towards the stomach
• Control of salivary secretion

  1. Salivary centre in medulla

  2. Parasympathetic (+)

  3. Sympathetic (-)

  4. Thinking about food

  5. Smell

  6. Sight

  7. Taste

  8. Presence of food in the mouth

  9. Pain receptors (temperature in mouth)
• Pavlovian classical conditioning


  Salivary secretion in response to stimuli associated with food
• Operant conditioning


  Learning through reinforcement or punishment
• Functions of saliva


  • Moistens and lubricates food
  • Digestion of starch to maltose and dextrins by amylase enzyme
  • Solubilise food to stimulate chemical receptors and taste buds
  • Health of teeth and gums (bacteriocidal agent)
  • Excretion of ions, drugs, microbes
  • Buffer (produce bicarbonate ions; maintain mouth pH 6.5 – 7.0)
  • Heat excretion (e.g. panting dog)
  • Aids human speech by wetting mouth area
• Carbohydrate digestion