1. The Intestines and Accessory Organs

2. The Intestines The small intestines are narrow (~2.5 cm wide), but up to ~630 cm long. There are 3 sections: - First ~30 cm: Duodenum - Next ~250 cm: Jejunum - Last ~350 cm: Ileum Jejunum Duodenum Ileum

3. The Duodenum 1) Chemical digestion continues in the duodenum. Carbohydrate, lipid, and protein digestion is almost completed.

4. The Duodenum The pancreas and the gall bladder are connected to the duodenum via ducts.

5. The Duodenum The gall bladder, pancreas, and liver are called accessory organs because food does not actually pass through them.

6. The Pancreas The pancreas is about 15 cm long and releases enzymes into the duodenum. These include: - proteases - carbohydrases - lipases - nucleases

7. The Pancreas Pancreatic juice also contains sodium bicarbonate to raise the pH of the chyme.

8. The Liver and Gall Bladder The liver makes bile (gall) : a substance that is able to attach to lipid globules and emulsify (separate) them into separate molecules. Extracted bile.

9. The Liver and Gall Bladder This emulsification enhances the activity of lipases by increasing the lipid surface area. It contains cholesterol and bile salts.

10. The Liver and Gall Bladder The gall bladder stores bile until it is needed. To duodenum From liver

11. The Liver and Gall Bladder Gall stones occur when the bile crystallizes inside the gall bladder. They may cause obstruction of the bile duct.

12. The Liver and Gall Bladder The secretions of the pancreas and gall bladder are controlled by hormones .

13. The Liver and Gall Bladder Secretin from the duodenum makes the pancreas secrete sodium bicarbonate and the gall bladder to secrete bile.

14. The Liver and Gall Bladder Cholecystokinen (CCK) from the duodenum make the pancreas secrete enzymes and the gall bladder to secrete bile. Also slows down the stomach.

15. The Jejunum 2) Digestion is completed in the jejunum and absorption is just beginning. This is the transitional section. Chyme has become chyle . Jejunum

16. The Jejunum Peptidases and disaccharidases are completing dipeptide and disaccharide digestion here.

17. The Jejunum Lined with longitudinal and circular muscles to perform peristalsis . Has villi.

18. The Ileum 3) Some absorption of nutrients takes place in the jejunum, but absorption primarily occurs in the ileum.

19. Absorption The surfaces of the jejunum and ileum that perform absorption are designed for maximum surface area for food to pass by.

20. Absorption - Villi

21. Absorption - Villi The surfaces are folded over, and each fold is has tiny projections called villi (singular villus).

22. Absorption - Villi Villi also have microvilli on them to further increase surface area.

23. Absorption - Villi - Villi contain capillaries for all nutrients except fats enter the bloodstream by. - Fats are absorbed by lacteals (the lymphatic system). Blood from heart Blood to to liver

24. Absorption - This nutrient-rich blood goes directly to the liver via the portal vein .

25. Absorption Nutrients enter villi (cross the membrane) by either active transport or passive transport .

26. Passive Transport Passive transport is the movement of molecules across a concentration gradient without using energy .

27. Passive Transport They move from high concentration to low concentration.

28. Passive Transport This works for small molecules like amino acids and monosaccharides. The diffusion of water has a special term: osmosis .

29. Passive Transport There are 2 types of passive transport: - Diffusion - Facilitated Diffusion

30. Passive Transport Diffusion occurs when a molecule can move itself across a membrane. Facilitated diffusion occurs when a protein must aid in the movement.

31. Active Transport Active transport requires a protein to use energy to help the molecule pass through the membrane. Energy

32. Active Transport Active transport is often used for large and/or charged molecules .

33. The Intestines

34. The Large Intestine The ileum empties its contents into the large intestine (also known as the colon).

35. The Large Intestine There ileum and colon are separated by the ileocecal valve (a sphincter).

36. The Large Intestine The large intestine of only ~1.5 m long, but it is ~7 cm wide.

37. The Large Intestine The sections of the large intestine all have similar functions and are named based on location.

38. The Large Intestine

39. The Appendix Attached to the cecum is the vestigial appendix, which is believed to have once held bacteria for cellulose digestion. Appendicitis is the inflammation of the appendix, which must then be removed.

40. The Appendix

42. The Large Intestine Diarrhea (watery or excessively loose feces) is caused by the improper functioning of the colon.

43. The Large Intestine There are also symbiotic bacteria ( E. coli ) in the colon which produce vitamin K, vitamin B12, thiamine, and riboflavin.

44. The Large Intestine Gas (carbon dioxide, methane, hydrogen sulhpide) is also produced in these bacterial reactions which is either absorbed or passed out the anus.

45. The Large Intestine The remaining bulk contains - some undigested food - indigestible food (fibre) - bile (dark greenish) - bilirubin (yellowish) from dead red blood cells.

46. The Rectum The colon empties into the rectum where waste is stored until it is ready to be egested.

47. The Rectum When it becomes full it triggers contractions to perform peristalsis for passing the waste through the anus.

48. The Anus The anus has 2 sphincters: - involuntary internal sphincter - voluntary external sphincter

49. The Anus An anal fissure is a split or tear in the anal canal caused by friction (ex. Excessive wiping) or stretching (ex. Constipation or straining while defecating)