Read the summary and the most important questions on Human Biology | 9780007267514 | Mike Boyle; Kathryn Senior

• 8 DIGESTION

• Why is large SA important for the absorption of food?

  It means that a lot of intestine area is in contact with lots of digested food molecules.
  
  Molecules are absorbed by diffusion or active transport; thus, the more membrane there is, the more pores and carrier proteins there are available.

• What is the significance of a good blood supply for the DS?

  It is a way to maintain the diffusion gradient so that there is always more digested food molecules on one side of the membrane than the other, thus ensuring that absorption is continuous and rapid.

• Why is it important for the DS to have thin wall?

  Fick's Law states that the speed of diffusion is inversely proportional to the diffusing distance. Thus, the thinner the membrane, the faster the diffusion.

• 8.1 THE HUMAN DIGESTIVE SYSTEM

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• What does it mean that humans are 'heterotrophs'?

  Humans cannot make their own food and must obtain it in the form of large organic molecules from other organisms. All those molecules were initially produced by green plants - autotrophs.

• What is the overall function of the digestive system?

  To break down the large molecules in food (protein & starch) into their monomers (AAs & sugars) for their easy absorption by the body.

• What are the 5 stages of the nutrition process?

  1. Ingestion
     
  2. Mechanical (physical) breakdown
  3. Digestion
  4. Absorption
  5. Egestion

• 8.2 STRUCTURE OF THE HUMAN DIGESTIVE SYSTEM

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• What is the structure of the human digestive system?

  Diagram of Human Digestive System

• What does the human digestive system consist of?

  The alimentary canal and its associated glands - salivary glands, liver & pancreas.

• What are the deep ridges of the stomach called and what is their role?

  Rugae and they help with the mechanical breakdown of food.

• What are the 4 overall functions of the stomach?

  1. Mix food with gastric juices
     
  2. Retain food, so enzymes have time to act
  3. Start the digestion of proteins through action of the enzyme pepsin
  4. Curdle milk with the enzyme rennin, & absorb some simple chemicals - water, salts as ions, and alcohol.