Nutrition in Humans (part 1): Digestion

1. Nutrition in Nutrition in Mammals Mammals

2. Lesson Objectives: Lesson Objectives: Holozoic Holozoic nutrition Introduction to the human digestive Introduction to the human digestive system system Digestion in the Digestion in the - - mouth mouth - - stomach stomach - - small intestine small intestine Absorption in the intestines (small Absorption in the intestines (small and large intestines) and large intestines) nutrition 1. 1. 2. 2. 3. 3. 4. 4.

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

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

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

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

7. Buccal Buccal Cavity (Mouth) Cavity (Mouth) Mechanical digestion Mechanical digestion 1. 1. *mastication large small Chemical digestion Chemical digestion 2. 2. amylase Starch maltose Starch maltose

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

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

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

12. *Peristalsis *Peristalsis

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

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

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

16. Gastric juice Gastric juice contains contains HCl rennin rennin pepsin pepsin HCl + 2 enzymes + 2 enzymes ? ? 1. 1. 2. 2. rennin insoluble casein soluble caseinogen pepsin proteins polypeptides

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

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

19. Small Intestine Small Intestine duodenum jejunum ileum

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

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

23. Pancreas Pancreas Connected to duodenum by Connected to duodenum by pancreatic duct pancreatic duct Secretes Secretes pancreatic juice pancreatic juice (digestive function) insulin insulin (controls blood glucose conc. & carbohydrate utilization) ? ? ? ? 1. 1. 2. 2.

24. Pancreatic juice Pancreatic juice Contains Contains pancreatic amylase pancreatic amylase pancreatic lipase pancreatic lipase pancreatic pancreatic trypsinogen (protease) (protease) ? ? 1. 1. 2. 2. trypsinogen 3. 3. ALT

25. Intestinal juice Intestinal juice secreted by glands lining small secreted by glands lining small intestine intestine contains contains sucrase sucrase maltase maltase enterokinase enterokinase erepsin erepsin lipase lipase lactase lactase ? ? enterokinase trypsinogen trypsin ? ? trypsin proteins polypeptides 1. 1. erepsin polypeptides amino acids 2. 2. 3. 3. 4. 4. 5. 5. SME2LL 6. 6.

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