Skills: Digestion & Absorption (DP IB Biology: HL)

Human Digestive System

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

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 the stomach and small intestine
    • Between the pancreas, small intestine and gall bladder

  • The shapes of organs should be approximately true to form e.g. the stomach should be a j-shaped sac
  • The liver should be 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

A diagram of the key components of the human digestive system

• 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 - 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 - the lining of the small intestine, composed of epithelium which is folded to form the villi

The layers of tissue in the wall of the small intestine

The layers of tissue in the wall of the small intestine as viewed under a microscope. Seen in both longitudinal section and cross section