Topic 6.1: Digestion

1. Topic 6.1: Digestion

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. Why do we digest? • When you eat a snack or a meal, you begin a set of events that leads to your body cells being provided with needed nutrients • Ingestion • Digestion • Absorption • Transport

4. Digestion • Digestion solves a problem of molecular size • Food is too large to pass through cell membranes • Food must be chemically digested to a suitable size

5. Digestion • Digestion allows you to turn molecules into ‘your own’ • All the food that you eat is composed of plant or animal cells, thus containing molecules characteristics of a living organisms that is not a human being • Each type of living organism has its own set of proteins, nucleic acids, and carboydrates

6. Digestion • When we digest food molecules, we break them down (hydrolyze them) into smallest components. • The components can be reassembled into larger molecules that are useful to you!!

7. Digestion • As food moves through your alimentary canal, many digestive enzymes are added along the way • Each digestive enzyme is specific for a specific food type • Examples: • Lipase: is an enzyme is specific for lipid molecules • Amylase: is specific for amylose(starch)

8. Digestion • The real function of enzyme is to lower the activation energy of reactions that they catalyze • Digestive enzymes all help to catalyze hydrolysis reactions

9. Examples of digestion enzymes

10. Human Digestive System • Much of the human digestive system is a tube called the alimentary canal • Alimentary canal consists of: • Mouth • Esophagus • Stomach • Small Intestine • Large Intestine (colon) • Rectum • Any foods that you ingest must either be digested and absorbed for use by the body or remain undigested and be eliminated as solid waste

11. Stomach • Food is brought to your stomach by a muscular tube called the esophagus • When you swallow, the food is forced down to your stomach by a sequential series of smooth muscle contractions called peristalsis

12. Stomach • 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 juice

13. Stomach • Gastric juice is a mixture of three secretions form the cells of the stomach inner lining: • 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 the stomach wall to prevent stomach damage from the hydrochloric acids

14. Stomach • The muscular wall of the stomach creates a churning motion in order to mix 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

15. Small Intestine • The first portion of the small intestine is called the duodenum • Three different accessory organs secrete juices into the small intestine in order to continue the digestive process • These secretions include: • Bile from the liver and gall bladder • Trypsin (a protease), lipase, amylase, and bicarbonate from the pancreas

16. Small Intestine • As the digestive process continues in the small intestine, molecules are produced that are small enough to be absorbed • The inner wall of the small intestine is made up of thousand of finger-like extensions called villi

17. Small Intestine • Each villus contains a capillary bed and a lacteal • Lacteal is a small vessel of your lymphatic system • If the inner lining of your small intestine were smooth, you would have a fairly limited membrane surface area for absorption • The function of the villi is to greatly increase the surface area for absorption of molecules such as glucose, amino acids, and fatty acids

18. Small Intestine • Most molecules absorbed are taken into the capillary bed within each villus • Except fatty acids which are more efficiently absorbed into the lacteal • All absorbed molecules are taken to a wide variety of body cells by the circulatory system

19. Large Intestine • The vast majority of useful nutrients are absorbed while food is still inside the small intestine • Much of the water that we drink or that is naturally contained in many food is also present

20. Large Intestine • The primary function of the large intestine is water absorption • Leaving water in the alimentary canal as long as possible is beneficial because it keeps the moving food in a fluid environment

21. Large Intestine • The large intestine is also home to a very large number of naturally occurring bacteria including Escherichia coli.

22. Large Intestine • These bacteria are examples of mutualistic organisms within us. • We provide nutrients, water, and a warm environment for them while they synthesize vitamin K and maintain a healthy overall environment for us in our large intestine • Any food undigested by us or the bacteria is eliminated from the body as solid waste or feces