THE DIGESTIVE SYSTEM

1. THE DIGESTIVE SYSTEM IT’S INTESTINE TIME!!

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3. MAIN IDEA OF INTESTINES • Small intestine where the major events of DIGESTION & almost all ABSORPTION occur • Large intestine where WATER ABSORPTION, vitamin production, and FECES FORMATION occurs

5. intestine VALVES! • Valve from stomach to small intestine (S.I.)  pyloric sphincter • Valve from the S.I. to L.I.  ileocecal valve/sphincter

6. 3 SECTIONS OF S.I. 1) **DUODENUM 2) JEJUNUM 3) ILEUM

7. MESENTERY • Layer of membrane (peritoneum) that holds the small intestine coiled together as well as to the posterior abdominal wall

8. 3 IMPORTANT FEATURES OF THE Small Intestine (S.I.): 1) CIRCULAR FOLDS  deep folds of both the mucosa and submucosa of small intestine (like rugae of stomach) *increase surface area PEYER’S PATCHES – collections of lymphatic tissue in submucosa; there are more at the end of S.I. because undigested food contains bacteria

9. 3 IMPORTANT FEATURES OF THE S.I. 2) VILLI  finger-like projections of mucosa that increase surface area Contain capillary beds and lymphatic capillaries (LACTEALS)

10. 3 IMPORTANT FEATURES OF THE S.I. 3) MICROVILLI  very tiny projections of membrane of mucosa cells on the VILLI ** Both villi & microvilli absorb digested foods through mucosa & submucosa

11. Small Intestine Note: ** Enzymes produced by the PANCREAS and bile made by the LIVER enter the DUODENUM!!

12. Chemical Digestion & Absorption in the S.I. • Chemical digestion is completed in the small intestine due to bile as well as enzymes in the pancreatic and intestinal juices. • Approx. 90% of all ABSORPTION takes place in the S.I.! (other % in stomach & L.I.)

13. SMALL INTESTINE labeled: First Figure/19.11 LABEL (p.472): • Duodenum • Jejunum • Ileum • Stomach • Large Intestine

14. SMALL INTESTINE labeled: Second Figure/19.12 LABEL (p 473): • Mucosa • Submucosa • Muscularis externa • Serosa • Villus • Blood capillary • Lacteal • Simple columnar epithelium

15. THE LARGE INTESTINE (L.I.)

16. LARGE INTESTINE • *Is much larger in diameter but shorter in length than the small intestine • runs from the ileocecal valve to the anus

17. LARGE INTESTINE (COLON) MAIN FUNCTIONS: • Dries out undigested food residue *absorbs water & vitamins • Eliminates residues from the body as wastes (feces)

18. 5 SECTIONS OF Large Intestine: 1) Cecum 2) Appendix 3) Colon (ascending colon, transverse colon, descending colon, and sigmoid colon) 4) Rectum 5) Anal Canal ANUS – opening to exterior

19. LARGE INTESTINE (L.I.) • The outer layer of the muscularisexterna is bundled into 3 bands called TENIA COLI which bunch up the colon into pouches called HAUSTRA Tenia = flat band Haustra = “drawer” puckered appearance

20. 2 valves in Anal Canal: - External voluntary sphincter (skeletal muscle) - Internal involuntary sphincter (smooth muscle)

21. Appendix • Hangs from the cecum(first section of L.I.) • Sometimes bacteria can get into appendix and it becomes inflamed = appendicitis • If it broke open it would empty its contents into the abdominopelvic cavity which could be fatal

22. Important Features of L.I. • There are NO villi  nutrient absorption into bloodstream happened in S.I. • LOTS of goblet cells in the simple columnar epithelium produce mucus (functions as lubricant)

23. BACTERIA • Bacteria live in the L.I. and break down some of the remaining nutrients which produces gas (flatulence) • FECES contain indigestible food materials, mucus, bacteria, and water

25. Digestion & Absorption in the L.I. • MECHANICAL DIGESTION in the large intestine includes: • HAUSTRAL churning or contraction of the haustra (pouches of colon) when the walls of the colon fill with chyme • PERISTALSIS (muscular contractions that propel food • MASS PERISTALSIS is a large peristaltic contraction that moves fecal material into RECTUM

26. DEFECATION REFLEX • Mass peristalsis moves indigestible materials from colon into the rectum: • Stretch receptors in the mucosa of the rectum are stimulated are the rectum is emptied • The internal involuntary sphincter opens due to a combination of pressure and parasympathetic nerve impulses

27. Chemical Digestion & Absorption in L.I. • The last small bit of digestion occurs in the L.I. by bacteria which break down any small carbohydrates, amino acids, etc. • Products of this breakdown include: gas (flatulence) as well as some vitamins

28. Chemical Digestion & Absorption in L.I. • L.I. absorbs mostly WATER and vitamins • Remember almost all absorption (including most water absorption happens in S.I.) • In the L.I. water is absorbed by osmosis

29. LARGE INTESTINE labeled: First Figure/19.14 LABEL (p 478): • Haustra • Tenia coli • Cecum • Ileocecal sphincter • Ileum • Ascending colon • Transverse colon • Descending colon • Sigmoid colon • Rectum • Anal canal • Anus

30. LARGE INTESTINE LABELED: Second Figure/19.15 LABEL (p 479): • Mucosa • Submucosa • Muscularisexterna • Serosa • Simple columnar epithelium

31. Accessory ORGANS Summary PANCREAS pancreatic enzymes that break down all 4 organic molecule groups are secreted into the duodenum

32. Accessory ORGANS Summary LIVER • 2 main lobes which are broken up into lobules • Produces bile which enters duodenum through the common hepatic duct • Bile breaks up fat molecules so that enzymes can digest them

33. Accessory ORGANS Summary GALLBLADDER  • On inferior surface of liver • Stores bile when food is not being digested

34. Accessory ORGANS Summary SALIVARY GLANDS • *Salivary amylase And salivary lipase TEETH • Mechanical digestion of food • Deciduous: first teeth/baby teeth