Digestive system

• What are the main two roles of the digestive system?

  Digestion - process of breaking down large food molecules into smaller molecules.

  Absorption - process of absorbing these small food molecules into the body.
• Name all the organs that food passes through, from the point it's eaten to the point it's excreted.

  Mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus.
• What is the role of teeth?

  Teeth chew food and physically break it down into smaller pieces. This has two purposes:

  1. It increases the surface area for enzymes to act on
  2. It makes the food easier to swallow.
• Oesophagus: A muscular tube that carries food from the mouth to the stomach.
• What are the three things the stomach does to aid digestion?

  1. Contracts its muscular walls to churn and mix food.
  2. Produces pepsin, which is a type of protease enzyme, and breaks proteins down into amino acids.
  3. Produces hydrochloric acid, which a) provides the right pH for pepsin to function, and b) kills microorganisms.
• Where is bile made and stored?

  Bile is made in the liver and stored in the gallbladder.
• What are the two roles of bile?

  1. To emulsify lipids, which means separate larger droplets of lipids into smaller droplets.
  2. To neutralise acid from the stomach, which bile can do because it is alkaline. This makes the acid pH more neutral, which is optimum for enzymes.
• What is the role of salivary glands?

  They produce saliva, which has two purposes:

  1. It moistens food, which makes it easier to swallow.
  2. It contains salivary amylase which digests starch to maltose.
• Which enzyme(s) does the pancreas produce?

  1. Carbohydrates - e.g. amylase.
  2. Proteases.
  3. Lipases.
• Which enzyme(s) does the stomach produce?

  Proteases - e.g. pepsin.
• Which enzyme(s) does the small intestine produce?

  1. Carbohydrates - e.g. amylase.
  2. Proteases.
  3. Lipases.
• What are the two roles of the small intestine?

  1. It is where most digestion takes place.
  2. It is where nutrients are absorbed into the bloodstream.
• What is the main role of the large intestine?

  To reabsorb water.
• What is the main role of the rectum?

  To store faeces until they're ready to be released.
• Give four ways in which villi are adapted to their role.

  1. There are many villi - giving them a large total surface area over which to absorb nutrients.
  2. Their walls have only a single layer of cells - nutrients only have to diffuse a short distance.
  3. They have a good supply of blood - maintains a strong concentration gradient between the lumen and the blood.
  4. The cells lining the villi have microvilli on the surface - further increases surface area.