The digestive system

• Mouth


  Ingestion process of taking food into the body by swallowing
• Mechanical digestion in the mouth

  Teeth, tongue and cheeks use force and pressure to break up the food into smaller bits
• Chemical digestion in the mouth

  1. Carbohydrates are acted on by amylase in saliva

  2. Saliva is a solution
• Salivary amylase


  One component in saliva
• Stomach (pH 2-3)


  • Mechanical digestion - waves of muscular contraction churn the food to mix it with gastric juice
  • Chemical digestion - gastric protease starts the breakdown of proteins
• Small intestine


  • Movement - segmentation
  • Mechanical digestion of fats from bile
  • Chemical digestion of all nutrients (protein, carbohydrates and lipids) from enzymes in the pancreatic juice
  • Absorption - nutrients diffuse into the circulatory system (proteins and glucose) and lymphatic system (fatty acids and glycerol)
• Liver


  Produces bile
• Gall bladder


  Stores bile (concentrates it) and releases bile when needed
• Liver and Gall bladder


  Emulsify fats - mechanical digestion, breaks big fat blobs into small fat droplets. There is no chemical change to the lipid molecule
• Pancreas


  • Produces pancreatic juice used for: Alkaline pH of 8 to neutralise stomach acid
  • Enzymes: Pancreatic amylase, Pancreatic protease, Pancreatic lipase
• Small intestine (6m long)

  • Villi and microvilli increase surface area
  • Very long length
  • Each villi has a good supply of blood vessels
• Segmentation vs Peristalsis


  Peristalsis moves food along, segmentation just mixes food and juices - no movement forward
• Large intestine (1.5m long)

  • Movement - remnant food material moves through the colon, it is mixed with bacteria and mucus, and formed into faeces for temporary storage before being eliminated
  • Reabsorption of water and mineral
• Appendix


  Vestigial organ
• The large intestine contains about 2kg of good bacteria which help to keep the body healthy
• Good bacteria


  Gute Bakterien
• Rectum and anus


  • Rectum connects the colon to the anus to hold the stool until defecation happens
  • Sphincters (circular muscles) relax and the rectum contracts
  • Anus allows control of stool, stops stool from coming out when it is not supposed to