The document summarizes digestion in the human digestive system. It describes the stages of digestion that occur in the mouth, stomach, and small intestine. In the mouth, mechanical and chemical digestion breaks down food. The stomach contains gastric glands that secrete enzymes and acid to digest proteins. The small intestine completes digestion with enzymes from the pancreas, liver, and intestinal walls that break down fats, proteins, and carbs into smaller molecules for absorption.

1. Nutrition in Mammals

2. Lesson Objectives: Holozoic nutrition Introduction to the human digestive system Digestion in the - mouth - stomach - small intestine Absorption in the intestines (small and large intestines)

3. Holozoic nutrition (feeding on ready made complex organic matter) Digestion : process where large food molecules are broken down into soluble and diffusible molecules that can be absorbed into the body cells Absorption : process whereby digested food materials are taken into the body cells Assimilation : process whereby some of the absorbed food materials are converted into new protoplasm or used to provide energy

4. Study tips: Always try to relate the structure of an organ with its function This serves as an easy way of remembering digestion facts! Picture the organ in your mind Identify the structures present Function of organ derived from structures present

5. Overview of the human digestive system Mouth ↓ Oesophagus ↓ Stomach ↓ Small Intestines ↓ Large Intestines ↓ Rectum ↓ Anus Mouth Stomach Small Intestine Pancreas Gall bladder Oesophagus

6. Types of digestion Mechanical digestion Break down particles into smaller pieces so as to increase the surface area for the action of enzymes. Chemical digestion Involves enzymatic reactions which digest the food into simpler chemical forms.

7. Buccal Cavity (Mouth) Mechanical digestion large small Chemical digestion Starch maltose amylase *mastication

9. Oesophagus Narrow muscular tube Wall consists of 4 layers - outermost layer ( serous coat ) -> moist & slippery (reduces friction when organs slide over each other) - smooth muscle - sub-mucous coat (layer of blood vessels & connective tissues) - mucous layer longitudinal muscle circular muscle (antagonistic)

10. serous coat - moist and slippery - layer of blood vessels & connective tissues - antagonistic smooth muscle sub-mucous coat mucous layer

11. Peristalsis Definition: Rhythmic wave-like contractions of the walls of the gut Caused by antagonistic action of muscles in gut wall i.e. when circular muscles contract, longitudinal muscles relax a. Causes the movement of content along the gut b. enables food to be mixed with digestive juices

12. *Peristalsis Muscles are antagonistic ( i.e. when one relaxes the other contracts and vice versa)

13. Stomach distensible, muscular bag (thick, well developed muscular walls)

14. Stomach structure muscle contracts -> entrance to small intestine closes muscle relaxes -> entrance to small intestine opens

15. Gastric glands - produces mucus which coats the surface epithelium - produces pepsinogen - produces HCl

16. Gastric juice contains HCl + 2 enzymes rennin pepsin soluble caseinogen insoluble casein rennin proteins polypeptides pepsin

17. Question to ponder: Do you think the enzymes in the stomach are produced in an active or inactive state?

18. Inactive enzymes Suggest reasons why the enzymes need to be produced in the inactive form. Ans: protect the stomach lining pepsinogen pepsin prorennin rennin HCl HCl

19. Small Intestine duodenum jejunum ileum

20. Pancreas, gall bladder & small intestine Cardiac sphincter Pyloric sphincter

21. Gall bladder yellowish green bag stores bile produced by the liver releases bile when it contracts via bile duct QUESTION: Can bile digest food? ANSWER: Bile is not an enzyme , so it cannot digest food but it aids in digestion of fats (by emulsifying fats)

22. Emulsification It is the process whereby large globules of fat are broken down into smaller globules How? Bile lowers the surface tension of fats i.e. reduce the attractive forces between the fat molecules This causes the fats to break into tiny fat droplets suspended in water , forming an emulsion (physical digestion) Purpose of emulsification -> increases s.a.:volume ratio -> speeds up digestion by lipase to f.a. + glycerol

23. Pancreas Connected to duodenum by pancreatic duct Secretes pancreatic juice (digestive function) insulin (controls blood glucose conc. & carbohydrate utilization)

24. Pancreatic juice Contains pancreatic amylase pancreatic lipase pancreatic trypsinogen (protease) ALT

25. Intestinal juice secreted by glands lining small intestine contains sucrase maltase enterokinase erepsin lipase lactase SME 2 LL polypeptides amino acids erepsin trypsinogen trypsin enterokinase proteins polypeptides trypsin

26. Summary: Pg.100 Biology Textbook Chapter 6:Nutrition in Humans *Summary of digestion in the human gut