Digestion

1. Digestion Topic 6.1

2. Assessment Statements • 6.1.1 Explain why digestion of large food molecules is essential. • 6.1.2 Explain the need for enzymes in digestion. • 6.1.3 State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. • 6.1.4 Draw and label a diagram of the digestive system. • 6.1.5 Outline the function of the stomach, small intestine and large intestine. • 6.1.6 Distinguish between absorption and assimilation. • 6.1.7 Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

3. Series of events • Ingestion • Digestion • Absorption • Transport

4. Why digestion of large molecules is essential • Large molecules are too big to pass across any cell membrane • Any food we eat must be chemically digested to a suitable size

5. Digestion allows you to turn molecules into ‘your own’ • Example: • You eat an egg • The egg white (albumin) contains an amino acid called serine • Your stomach/small intestine digests the albumin • Serine diffuses through the cells of the small intestine and then into a capillary • Serine is enters a pancreas cell • The cell uses the genetic code of your DNA to build serine into insulin • Benefits of digestion: • Serine is able to leave the albumin and enter the bloodstream • Serine helps to synthesize your own protein under the control of your DNA

6. Need for enzymes To lower activation energy To catalyze hydrolysis reactions Converts large macromolecules to smaller molecules that can be absorbed and then used Amylase puts stress on bonds of glucose held together in a starch molecule Surrounding thermal energy provides molecular motion to break the bonds • Enzymes are protein molecules which act as catalysts for reactions • They lower the activation energy of the reactions that they catalyze • Reactions occurring with an enzyme can occur with a lower input of energy than the same reaction without the aid of an enzyme

7. Examples of digestive enzymes

8. Digestive system • Any foods you ingest must either be digested and absorbed for use by the body or remain undigested and be eliminated as solid waste (faeces)

9. Stomach • Food brought to stomach by oesophagus • When you swallow, the food is forced down to your stomach by peristalsis • Once in the stomach, the food is held for a period of time in order to mix it with a variety of secretions collectively known as gastric juices • Pepsin – a protease enzyme most active in acidic pH • Hydrochloric acid – helps degrade and break down foods and creates the acidic pH necessary for pepsin to be active • Mucus – lines the inside of the stomach wall to prevent stomach damage from the hydrochloric acid

10. The muscular wall of the stomach creates a churning motion in order to mix the food with the gastric juice • After a period of time, a valve at the lower end of the stomach opens and the food enters the small intestine

11. What are you eating in a day? • How to read food labels • Record the nutrition facts for all of the food that you consume in one day

12. Small intestine • 1st portion is called the duodenum • Secretions are emptied here in order to continue the digestive process: • Bile from liver and gall bladder • Trypsin (a protease), lipase, amylase and bicarbonate from the pancreas

13. Small intestine villi • Molecules are produced that are small enough to be absorbed • Inner wall of small intestine is made up of thousands of finger-like extensions called villi which functions to increase surface area for absorption • Each villus contains a capillary bed and a lacteal (a small vessel of lymphatic system)

15. Absorption Assimilation Molecules taken into capillary bed and lacteal Taken to a wide variety of body cells Used for building larger molecules • Molecules taken into capillary bed and lacteal • Taken to a wide variety of body cells • Used for energy

16. Large intestine