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THE DIGESTIVE SYSTEM

Learn about the important functions and features of the small and large intestines, including digestion, absorption, and waste elimination. Explore the valves, sections, and structure of the intestines. Understand the role of bacteria in digestion and the process of defecation.

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THE DIGESTIVE SYSTEM

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  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

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

  5. 3 SECTIONS OF S.I. 1) **DUODENUM 2) JEJUNUM 3) ILEUM

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

  7. 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

  8. 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)

  9. 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

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

  11. 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.)

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

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

  14. THE LARGE INTESTINE (L.I.)

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

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

  17. 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

  18. 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

  19. 2 valves in Anal Canal: - External voluntary sphincter (skeletal muscle) - Internal involuntary sphincter (smooth muscle)

  20. 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

  21. 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)

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

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

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

  30. 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

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

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

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