Chapter 6 Nutrition in Humans Lesson 1 - The Need for Digestion

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  • 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
  • 8.  
  • 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