1. The Digestive System
Human Digestion

2. Digestion
Process by which food molecules are broken down into simpler molecules that can be absorbed and used by the cells of the body
Nutrients are passed through cell membrane (absorption) but large particles must be broken down first.

3. Mechanical Breakdown
Chewing and cutting (teeth)

4. Chemical Breakdown
Digestive enzymes (saliva)

5. The Human Digestive System
Oral cavity (mouth)
Pharynx (throat)
Esophagus (gullet)
Stomach
Small intestine
Large intestine
Rectum
Anus
Food passes through the digestive tube in the following order

6. The Human Digestive System

7. The Mouth and Pharynx
Mechanical breakdown of food

8. The Mouth and Pharynx
Mechanical breakdown of food
Teeth

9. The Mouth and Pharynx Food mixed with saliva
3 pair of salivary glands in mouth

10. The Mouth and Pharynx Saliva wets food and causes it to stick together
Bolus – food mass

11. The Mouth and Pharynx Chemical digestion in mouth with saliva
Salivary amylase – enzyme in saliva that breaks starch into maltose and glucose

12. The Mouth and Pharynx Food pushes into pharynx
Epiglottis – flap of tissue covering trachea or pharynx so food/air goes down the right tube

13. Esophagus
Tube through which food passes from pharynx to stomach

14. Esophagus
Sphincter Muscle – ring of muscle where esophagus tube meets stomach

15. Esophagus
Peristalsis – rhythmic muscular movement of organs that “pushes” food through digestive tract

16. Stomach Food broken down! Mechanically: stomach contractions
Chemically: gastric juices secreted by glands in stomach walls

17. Stomach Glands
Pyloric Gland – secretes mucus to cover stomach lining and protect it
Gastric Gland – secretes gastric juices
a. pH of 1.5 – 2.5 (acidic)
b. Contains HCl (hydrochloric acid) and pepsin (digestive enzyme that breaks down protein and curdles milk)

18. Stomach 3 mechanisms that stimulate the flow of gastric juices:
1. Thought, smell, sight, or taste of food sends message from brain to gastric gland
2. Food touching the stomach lining

19. Stomach 3. When food mass stretches stomach walls
Stretching stimulates lining to secrete gastrin (hormone) into blood stream
Gastrin signals gastric glands to produce large amounts of gastric juices

20. Stomach
Liquids pass through stomach in

21. Stomach
Liquids pass through stomach in
20 minutes or less

22. Stomach
Solids

23. Stomach Solids take longer
Reduced to thin soupy liquid – Chyme – that passes through Pyloric Sphincter (muscle controlling passage of chyme from stomach to small intestine)

24. Stomach
ULCER – mucus layer of stomach breaks down and part of stomach wall is digested

25. Small Intestine Fluids are alkaline
Chyme is mixed with bile from liver, pancreatic juice from pancreas, and intestine juice from small intestine

26. Small Intestine Peristalsis * squeezes chyme through intestine
* mixes chyme with digestive enzymes
* breaks down chyme mechanically
* speeds absorption by bringing contents into contact with intestinal walls

27. Small Intestine Pancreatic Enzymes a. Amylase – breaks starch into
maltose

28. Small Intestine Pancreatic Enzymes a. Amylase – breaks starch into
maltose
b. Protease – breaks proteins
 trypsin
 chymotrypsin

29. Small Intestine Pancreatic Enzymes a. Amylase – breaks starch into
maltose
b. Protease – breaks proteins
 trypsin
 chymotrypsin
c. Lipase – breaks lipids

30. Small Intestine
Bile – from cells of liver and is stored in gallbladder
Aids in digestion of fats and oils by breaking them into tiny droplets – emulsification – and increases surface area for enzyme action

31. Small Intestine
Intestinal Juices – walls of small intestine contains millions of intestinal glands that secrete intestinal juices

32. Small Intestine
Absorption – small intestine is site of absorption of substances into blood vessels of circulatory system

33. Small Intestine
Small intestine contains folds and lining is covered with projections called villi

34. Large Intestine
Undigested and unabsorbed materials pass from small intestine to large intestine
NO digestion occurs here

35. Large Intestine
Lower right side of body where small intestine and large intestine meet is a pouch - appendix

36. Large Intestine
Main function of large intestine is reabsorption of water from food mass

37. Large Intestine
Main function of large intestine is reabsorption of water from food mass
Second function is to absorb vitamins produced by bacteria normally living in large intestine
Bacteria live on undigested food material and in turn produce vitamin K which is essential for blood clotting

38. Large Intestine
Third function is to eliminate undigested or indigestible material (feces)

39. Rectum
Stores feces

40. Anus
Feces eliminated from body here
THE END!