1. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.1 The Components of the Digestive System

2. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ingestion Mechanical processing Digestion Secretion Absorption Excretion Functions of the digestive system

3. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Visceral smooth muscle shows rhythmic cycles of activity Pacemaker cells Peristalsis Waves that move a bolus Segmentation Churn and fragment a bolus Movement of digestive materials

4. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Peristalsis Figure 24.4

5. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Movement of materials along the digestive tract is controlled by: Neural mechanisms Hormonal mechanisms Enhance or inhibit smooth muscle contraction Local mechanisms Coordinate response to changes in pH or chemical stimuli Control of the digestive system

6. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings ]The Regulation of Digestive Activities Figure 24.5

7. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Its functions include: Analysis of material before swallowing Mechanical processing by the teeth, tongue, and palatal surfaces Lubrication Limited digestion The mouth opens into the oral or buccal cavity

8. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 8 Anatomy of the Mouth and Throat

9. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 9 Human Deciduous and Permanent Teeth

10. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 10 Dorsal Surface of the Tongue

11. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings primary functions include: Mechanical processing Assistance in chewing and swallowing Sensory analysis by touch, temperature, and taste receptors The tongue

12. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Common passageway for food, liquids, and air Lined with stratified squamous epithelium Pharyngeal muscles assist in swallowing Pharyngeal constrictor muscles Palatal muscles The pharynx

13. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Esophagus Figure 24.10a-c

14. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 14 Deglutition (swallowing) Sequence Voluntary stage Push food to back of mouth Pharyngeal stage Raise Larynx + hyoid Tongue to soft palate Esophageal stage Contract pharyngeal muscles Open esophagus Start peristalsis

15. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 15 Deglutition (swallowing) Control Nerves Glossopharyngeal Vagus Accessory Brain stem Deglutition center Medulla oblongata Pons Disorders Dysphagia Aphagia

16. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 16 Esophagus Sphincters Upper Lower

17. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Abnormalities Achalasia – lower esophagus muscles don’t relax- doesn’t allow food to pass through Atresia- esophogus openings are closed shut (Birth Defect) Hernia- Esophogus pushes into stomach Barret ’ s esophagus- tissue is more like intestinal lining tissue- can develop a rare cancer from this Esophageal varices- enlarged veins that can leak blood

18. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Bulk storage of undigested food Mechanical breakdown of food Disruption of chemical bonds via acids and enzymes Functions of the stomach

19. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Preliminary digestion of proteins Pepsin Permits digestion of carbohydrates Very little absorption of nutrients Some drugs, however, are absorbed Mucous secretion containing several hormones Enteroendocrine cells (Endocrine= Hormones!) G cells secrete gastrin – stimulates pareital cells to secrete HCL D cells secrete somatostatin- inhibits gastric secretions Digestion and absorption in the stomach

20. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Stomach Figure 24.12b

21. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Stomach Lining Figure 24.13a, b

22. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Stomach Lining Figure 24.13c, d

23. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-23 Stomach Histology Gastric pits: openings for gastric glands. Lined with simple columnar epithelium Cells of gastric pits Surface mucus: mucus that protects stomach lining from acid and digestive enzymes Mucous neck: mucus Parietal: hydrochloric acid and intrinsic factor Chief: pepsinogen Endocrine: regulatory hormones Gastrin-containing cells: secrete gastrin (a hormone that stimulates acid secretion) Somatostatin-containing cells: secrete somatostatin that inhibits gastrin and insulin secretion

24. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-24 Secretions of the Stomach Chyme: ingested food plus stomach secretions Mucus: surface and neck mucous cells Viscous and alkaline Protects from acidic chyme and enzyme pepsin Irritation of stomach mucosa causes greater mucus Intrinsic factor: parietal cells. Binds with vitamin B12 and helps it to be absorbed in the ileum. B12 necessary for DNA synthesis and RBC production (lack of B12 absorption leads to pernicious anemia)

25. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Secretions of the Stomach HCl: parietal cells Kills bacteria (found in ingested food) Stops carbohydrate digestion by inactivating salivary amylase Denatures proteins Helps convert pepsinogen to pepsin (optimal activity at pH 3 or less) Pepsinogen: packaged and released by exocytosis. Pepsin catalyzes breaking of covalent bonds in proteins (breaks them into smaller peptide chains)

26. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-26 Cephalic Phase The taste or smell of food, tactile sensations of food in the mouth, or even thoughts of food stimulate the medulla oblongata. Parasympathetic action potentials are carried by the vagus nerves to the stomach, where enteric plexus neurons are activated. Neurons stimulate secretion by parietal and chief cells (HCl and pepsin) and stimulate the secretion of the hormone gastrin and histamine. Gastrin is carried through the circulation back to the stomach where it and histamine stimulate further secretion of HCl and pepsin.

27. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-27 Gastric Phase Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata. Medulla oblongata stimulates further secretions of the stomach. Distention also stimulates local reflexes that amplify stomach secretions.

28. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-28 Intestinal Phase 1.Chyme in the duodenum with a pH less than 2 or containing lipids inhibits gastric secretions by three mechanisms 2.Sensory input to the medulla from the duodenum inhibits the motor input from the medulla to the stomach. Stops secretion of pepsin and HCl. 3.Local reflexes inhibit gastric secretion 4.Secretin, and cholecystokinin produced by the duodenum decrease gastric secretions in the stomach.

29. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-29 Movements in Stomach Combination of mixing waves (80%) and peristaltic waves (20%) Both esophageal and pyloric sphincters are closed.

30. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Important digestive and absorptive functions Secretions and buffers provided by pancreas, liver, gall bladder Three subdivisions: Duodenum Jejunum Ileum Ileocecal sphincter Transition between small and large intestine Small intestine

31. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.16a Figure 24.16 Regions of the Small Intestine

32. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Plicae Transverse folds of the intestinal lining Villi Fingerlike projections of the mucosa Lacteals Terminal lymphatic in villus Intestinal glands Lined by enteroendocrine, goblet and stem cells Histology of the small intestine

33. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-33 Modifications to Increase Surface Area Increase surface area 600 fold Plicae circulares (circular folds) Villi that contain capillaries and lacteals. Folds of the mucosa Microvilli: folds of cell membranes of absorptive cells

34. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.17a The Intestinal Wall

35. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.17b, c The Intestinal Wall

36. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.17d, e The Intestinal Wall

37. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Moisten chyme Help buffer acids Maintain digestive material in solution Intestinal juices

38. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-38 Mucosa and Submucosa of the Duodenum Cells and glands of the mucosa Absorptive cells: cells with microvilli, produce digestive enzymes and absorb digested food Goblet cells: produce protective mucus Endocrine cells: produce regulatory hormones (Secretin, and cholecystokinin) Granular cells (paneth cells): may help protect from bacteria (contain lysozymes) Intestinal glands (crypts of Lieberkühn): tubular glands in mucosa at bases of villi [secrete sucrase,maltase, trypsin, chymotrypsin, and pepsin (endopeptidases and exopeptidases) ] Duodenal glands (Brunner’s glands): tubular mucous glands of the submucosa. Open into intestinal glands [produce a mucus-rich alkaline secretion (containing bicarbonate)

39. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-39 Jejunum and Ileum Gradual decrease in diameter, thickness of intestinal wall, number of circular fold, and number of villi the farther away from the stomach Major site of nutrient absorption Peyer’s patches: lymphatic nodules numerous in mucosa and submucosa Ileocecal junction: where ileum meets large intestine. Ileocecal sphincter (ring of smooth muscle) and ileocecal valve (one-way valve)

40. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-40 Liver, Gallbladder, Pancreas and Ducts

41. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.18a-c The Pancreas

42. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-42 Pancreatic Secretions: Pancreatic Juice Enzymatic portion: (without the enzymes produced by pancreas, lipids, proteins, & carbs not adequately digested) Trypsinogen- active form is trypsin--------proteolytic enzyme Chymotrypsinogen- active form is chymotrypsin--------proteolytic enzyme Procarboxypeptidase- active form is carboxypeptidase ------- proteolytic enzyme Pancreatic amylase- continues digestion of starch. Pancreatic lipases- lipid digesting enzyme Deoxyribonucleases and ribonucleases- reduce DNA & RNA to their nucleotide Interaction of duodenal and pancreatic enzymes Enterokinase is a proteolytic enzyme from the duodenal mucosa and it activates trypsinogen to trypsin. Trypsin activates chymotrypsinogen to chymotrypsin. Trypsin activates procarboxypeptidase to carboxypeptidase.

43. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-43 Liver Histology Hepatic cords: radiate out from central vein. Composed of hepatocytes Hepatic sinusoids: between cords, lined with endothelial cells and hepatic phagocytic (Kupffer) cells Bile canaliculus: between cells within cords Hepatocyte functions Bile production Storage Interconversion of nutrients Detoxification Synthesis of blood components

44. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-44 Functions of the Liver Bile production: 600-1000 mL/day. Bile salts, bilirubin (bile pigment that results from breakdown of hemoglobin), cholesterol, fats, fat-soluble hormones, lecithin Neutralizes and dilutes stomach acid (neutralizes chyme so that pancreatic enzymes can function) Bile salts emulsify fats. Most are reabsorbed in the ileum. (90% bile salts reabsorbed in the ileum & carried back to liver) Secretin (from the duodenum) stimulates bile secretions, increasing water and bicarbonate ion content of the bile Storage Glycogen, fat, vitamins (A, B12, D, E, and K), copper and iron. Hepatic portal blood comes to liver from small intestine (nutrients are stored and secreted back into circulation when needed) Synthesis Blood proteins: Albumins, fibrinogen, globulins, heparin, clotting factors (liver produces its own new compounds)

45. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-45 Liver Lobes Major: Left and right Minor: Caudate and quadrate Porta: on inferior surface. Vessels, ducts, nerves, exit/enter liver Hepatic portal vein, hepatic artery, hepatic nerve plexus enter Lymphatic vessels, two hepatic ducts exit Ducts –Right and left hepatics (which transport bile out of liver) unite to form –Common hepatic –Cystic: from gallbladder –Common bile: union of cystic duct and common hepatic duct

46. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.19b, c The Anatomy of the Liver

47. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.20a, b Liver Histology

48. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Hollow, pear-shaped organ Stores, modifies and concentrates bile The gallbladder

49. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.21a, b The Gallbladder

50. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-50 Large Intestine Extends from ileocecal junction to anus Consists of cecum, colon, rectum, anal canal Movements sluggish (18-24 hours); chyme converted to feces. Absorption of water and salts, secretion of mucus, extensive action of microorganisms are involved in the formation of feces. 1500 mL chyme enter the cecum, 90% of volume reabsorbed yielding 80-150 mL of feces

51. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.23a The Large Intestine

52. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-52 Anatomy of Large Intestine Cecum Blind sac, appendix attached. Appendix walls contain numerous lymph nodules Colon Ascending, transverse, descending, sigmoid Mucosa has numerous straight tubular glands called crypts. Goblet cells predominate, but there are also absorptive and granular cells as in the small intestine

53. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.23b, c The Large Intestine

54. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-54 Anatomy of Large Intestine Rectum Straight muscular tube, thick muscular tunic Anal canal- superior epithelium is simple columnar; inferior epithelium is stratified squamous Internal anal sphincter (smooth muscle) External anal sphincter (skeletal muscle) Hemorrhoids: Vein enlargement or inflammation

55. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-55 Secretions of Large Intestine Mucus provides protection Pumps: bacteria remove acid from the epithelial cells that line the large intestine Bacteria produce gases (flatus) from particular kinds of carbohydrates found in legumes and in artificial sugars like sorbitol Bacteria produce vitamin K which is then absorbed Feces consists of water, undigested food (cellulose), microorganisms, sloughed-off epithelial cells

56. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 24-56 Movement in Large Intestine Mass movements (strong contractions) Common after meals Local reflexes instigated by the presence of food in the stomach and duodenum Gastrocolic: initiated by stomach Duodenocolic: initiated by duodenum Defecation Defecation reflex: distension of the rectal wall by feces Parasympathetic stimulation Usually accompanied by voluntary movements to expel feces. Abdominal cavity pressure caused by inspiration and by contraction of muscles of abdominal wall.

57. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Absence of villi Presence of goblet cells Deep intestinal glands Histology of the large intestine

58. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 24.25 The Defecation Reflex

59. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Begins in the mouth Salivary and pancreatic enzymes Disaccharides and trisaccharides Brush border enzymes Monosaccharides Absorption of monosaccharides occurs across the intestinal epithelia Carbohydrate digestion and absorption

60. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lipid digestion utilizes lingual and pancreatic lipases Bile salts improve chemical digestion by emulsifying lipid drops Lipid-bile salt complexes called micelles are formed Micelles diffuse into intestinal epithelia which release lipids into the blood as chylomicrons Lipid digestion and absorption

61. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Low pH destroys tertiary and quaternary structure Enzymes used include pepsin, trypsin, chymotrypsin, and elastase Liberated amino acids are absorbed Protein digestion and absorption

62. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Water Nearly all that is ingested is reabsorbed via osmosis Ions Absorbed via diffusion, cotransport, and active transport Vitamins Water soluble vitamins are absorbed by diffusion Fat soluble vitamins are absorbed as part of micelles Vitamin B 12 requires intrinsic factor Absorption

63. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive Secretion and Absorption of Water Figure 24.27