IB Biology SL

Revision Notes

6.1.4 Skills: Digestion & Absorption

Digestive System Diagram

Human Digestive System

  • The human digestive system includes the following:
    • Glands – the salivary glands and glands in the pancreas produce digestive juices
    • The stomach and small intestine – the sites of digestion
    • The liver – produces bile
    • Small intestine – the site of absorption
    • Large intestine – site of water reabsorption

Tips for drawing an annotated digestive system diagram

  • A simple annotated diagram should include some clear features:
    • The junctions between each section should be obvious and unobstructed or covered by other parts of your drawing, this includes the following junctions:
      • Between the stomach and oesophagus
      • Between stomach and small intestine
      • Between pancreas, small intestine and gall bladder
    • The organs should be shaped approximately true to form e.g. the stomach should be a j-shaped sac
    • The liver the largest organ represented and located to the left of the stomach
    • The diameter of the small intestine needs to be obviously smaller than the diameter of the large intestine

Exam Tip

Draw your diagrams using a dark pen or pencil to ensure that all components are clear (even after scanning)

Small Intestine: Identifying Tissue Layers

  • The wall of the small intestine is made up of several layers including the following:
    • Serosa – an outer coat which includes a membrane and connective tissue
    • Muscle layer (muscularis externa) – including longitudinal muscle tissue in the outermost layer with a layer of circular muscle tissue on the inside
    • Sub-mucosa – connective tissue containing blood and lymph vessels
    • Mucosa – an inner lining of the small intestine composed of the epithelium which is folded to form the villi

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