Physical digestion

• Physical digestion


  The breakdown of food into smaller pieces without chemical changes to the food molecules
• Physical digestion


  • Increases the surface area of food for the action of enzymes in chemical digestion
• Physical digestion in the mouth


  1. Teeth chew the food into smaller pieces

  2. Food is passed to the stomach in the form of a bolus

  3. Food is broken down further by enzymes
• Types of human teeth


  • Incisors
  • Canines
  • Premolars
  • Molars
• Incisors


  Chisel shaped with sharp edges for cutting off pieces of food
• Canines


  Slightly larger and more pointed, perform a similar function to incisors
• Premolars


  Have one or two roots that secure them to the jaw, two knobbly surfaces called cusps which crush and grind the food into small particles
• Molars


  Have four or five cusps instead of two, and two or three roots, function is similar to premolars
• Tooth structure


  Crown - exposed part above the gum line

  Root - portion below the gum line

  Enamel - extremely hard, wear resistant substance lining the crown

  Dentine - softer substance below the enamel that reinforces the structure

  Pulp cavity - contains blood vessels and nerve cells
• Physical digestion in the stomach


  1. Stomach wall contains layers of muscle that alternately contract and relax, churning and squeezing the food

  2. Mixes the food with gastric juice

  3. Breaks the food down into a liquid
• Bile


  Green watery fluid produced by the liver, stored in the gallbladder, released into the duodenum

  Contains bile salts that emulsify or break down large lipid particles into small droplets with a large surface area

  Droplets are then chemically digested by the enzyme lipase