Biolgy-Digestive System

• Digestion


  Breakdown of large insoluble molecules to small soluble molecules to be absorbed into the blood stream
• Stages of digestion


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Egestion
• Digestive system


  • Organs: mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus
  • Functions: ingestion, digestion, absorption, assimilation, egestion
• Ingestion


  Intake of food
• Chemical processes in the mouth


  Enzymes (chemicals) that help to breakdown the food
• Physical processes in the mouth


  Chewing, peristalsis (contraction and relaxation of muscle in the oesophagus), churning in the stomach
• Types of teeth


  • Incisors
  • Canines
  • Premolars
  • Molars
• Canines


  Ripping and tearing
• Tooth structure


  • Crown
  • Root
  • Enamel
  • Dentine
  • Pulp cavity
• Enamel is the hardest substance in the body and is transparent
• Dentine protects the pulp cavity and gives the tooth its colour
• Pulp cavity contains the tooth's nerves and blood vessels
• Tooth decay


  Caused by too much sugar in the diet or poor dental hygiene
• Cause of tooth decay


  Sugar + bacteria = acid
• Disclosure tablets help identify bacteria on teeth
• Most bacteria is found at the gumline and back teeth
• Reason for bacteria location

  Harder to clean these areas
• Advice for maintaining healthy teeth


  • Brush twice a day
  • Floss
  • Visit dentist every 6 months
• Oesophagus


  Food travels down by peristalsis
• Epiglottis


  Prevents food going down the windpipe
• Stomach


  Muscular bag
• Acid in stomach


  Kills bacteria
• Physical breakdown in stomach

  Churning by contraction and relaxation of stomach walls
• Bile


  Neutralises acid, emulsifies fat
• Small intestine


  • Roughly 6m long, absorption takes place here, contains villi to increase surface area
• Villi


  • Large surface area, good blood supply, permeable walls
• Assimilation


  Nutrients pass into blood stream and are transported around the body
• Large intestine


  Removes water from unabsorbed food, stores undigested food
• Egestion


  Undigested food passes out through the anus