1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 23 The Digestive System: Part C

2. Copyright © 2010 Pearson Education, Inc. Pancreas Location Mostly retroperitoneal, deep to the greater curvature of the stomach Head is encircled by the duodenum; tail abuts (meets up/points toward) the spleen

3. Copyright © 2010 Pearson Education, Inc. Pancreas Endocrine function Pancreatic islets secrete insulin and glucagon Exocrine function Acini (clusters of secretory cells) secrete pancreatic juice

4. Copyright © 2010 Pearson Education, Inc. Figure 23.26a Small duct Acinar cells Basement membrane Zymogen granules Rough endoplasmic reticulum (a)

5. Copyright © 2010 Pearson Education, Inc. Pancreatic Juice Watery alkaline solution (pH 8) neutralizes chyme Electrolytes (primarily HCO 3 – ) Enzymes Amylase, lipases, nucleases are secreted in active form but require ions or bile for optimal activity

6. Copyright © 2010 Pearson Education, Inc. Pancreatic Juice Protease activation in duodenum Trypsinogen is activated to trypsin by brush border enzyme enteropeptidase Procarboxypeptidase and chymotrypsinogen are activated by trypsin

7. Copyright © 2010 Pearson Education, Inc. Figure 23.27 Stomach Pancreas Epithelial cells Trypsinogen (inactive) Chymotrypsinogen (inactive) Procarboxypeptidase (inactive) Trypsin Chymotrypsin Carboxypeptidase Membrane-bound enteropeptidase

8. Copyright © 2010 Pearson Education, Inc. Regulation of Bile Secretion Bile secretion is stimulated by Bile salts in enterohepatic circulation Secretin from intestinal cells exposed to HCl and fatty chyme

9. Copyright © 2010 Pearson Education, Inc. Regulation of Bile Secretion Gallbladder contraction is stimulated by Cholecystokinin (CCK- peptide hormone) from intestinal cells exposed to proteins and fat in chyme CCK also causes the hepatopancreatic sphincter to relax

10. Copyright © 2010 Pearson Education, Inc. Regulation of Pancreatic Secretion CCK induces the secretion of enzyme-rich pancreatic juice by acini Secretin causes secretion of bicarbonate-rich pancreatic juice by duct cells Vagal stimulation also causes release of pancreatic juice (minor stimulus)

11. Copyright © 2010 Pearson Education, Inc. Figure 23.28 Chyme enter- ing duodenum causes release of cholecystokinin (CCK) and secretin from duodenal enteroendocrine cells. CCK (red dots) and secretin (yellow dots) enter the bloodstream. CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO 3 – -rich pancreatic juice. Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly. CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum. During cephalic and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder. Slide 1 1 2 3 4 5 6

12. Copyright © 2010 Pearson Education, Inc. Digestion in the Small Intestine Chyme from stomach contains Partially digested carbohydrates and proteins Undigested fats

13. Copyright © 2010 Pearson Education, Inc. Requirements for Digestion and Absorption in the Small Intestine Slow delivery of hypertonic chyme Delivery of bile, enzymes, and bicarbonate from the liver and pancreas Mixing

14. Copyright © 2010 Pearson Education, Inc. Motility of the Small Intestine Segmentation Initiated by intrinsic pacemaker cells Mixes and moves contents slowly and steadily toward the ileocecal valve

15. Copyright © 2010 Pearson Education, Inc. Figure 23.3b (b) Microvilli Absorptive cell

16. Copyright © 2010 Pearson Education, Inc. Motility of the Small Intestine Peristalsis Each wave starts distal to the previous (the migrating motility complex) Meal remnants, bacteria, and debris are moved to the large intestine

17. Copyright © 2010 Pearson Education, Inc. Figure 23.3a From mouth (a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally.

18. Copyright © 2010 Pearson Education, Inc. Motility of the Small Intestine Local enteric neurons coordinate intestinal motility Causes contraction of the circular muscle proximally and of longitudinal muscle distally Forces chyme along the tract

19. Copyright © 2010 Pearson Education, Inc. Motility of the Small Intestine Ileocecal sphincter relaxes and admits chyme into the large intestine when Gastroileal reflex enhances the force of segmentation in the ileum Gastrin(hormone) increases the motility of the ileum Ileocecal valve flaps close when chyme exerts backward pressure

20. Copyright © 2010 Pearson Education, Inc. Large Intestine Regions Cecum (pouch with attached vermiform appendix) Colon Rectum Anal canal

21. Copyright © 2010 Pearson Education, Inc. Figure 23.29a Left colic (splenic) flexure Transverse mesocolon Epiploic appendages Descending colon Teniae coli Sigmoid colon Cut edge of mesentery External anal sphincter Rectum Anal canal (a) Right colic (hepatic) flexure Transverse colon Superior mesenteric artery Haustrum Ascending colon IIeum IIeocecal valve Vermiform appendix Cecum

22. Copyright © 2010 Pearson Education, Inc. Colon Ascending colon and descending colon are retroperitoneal

23. Copyright © 2010 Pearson Education, Inc. Figure 23.30c Transverse colon Greater omentum Descending colon Jejunum Mesentery Transverse mesocolon Sigmoid mesocolon Sigmoid colon Ileum (c)

24. Copyright © 2010 Pearson Education, Inc. Figure 23.30d (d) Pancreas Liver Lesser omentum Stomach Duodenum Transverse mesocolon Greater omentum Mesentery Jejunum Visceral peritoneum Urinary bladder Transverse colon Ileum Parietal peritoneum Rectum

25. Copyright © 2010 Pearson Education, Inc. Rectum and Anus Rectum Three rectal valves stop feces from being passed with gas Anal canal The last segment of the large intestine Sphincters Internal anal sphincter—smooth muscle External anal sphincter—skeletal muscle

26. Copyright © 2010 Pearson Education, Inc. Figure 23.29b (b) Rectal valve Rectum Anal canal Levator ani muscle Anus Anal sinuses Anal columns Internal anal sphincter External anal sphincter Hemorrhoidal veins Pectinate line

27. Copyright © 2010 Pearson Education, Inc. Large Intestine: Microscopic Anatomy Mucosa of simple columnar epithelium except in the anal canal (stratified squamous) Abundant deep crypts with goblet cells Superficial venous plexuses of the anal canal form hemorrhoids if inflamed

28. Copyright © 2010 Pearson Education, Inc. Bacterial Flora Enter from the small intestine or anus Colonize the colon Ferment indigestible carbohydrates Release irritating acids and gases Synthesize B complex vitamins and vitamin K

29. Copyright © 2010 Pearson Education, Inc. Functions of the Large Intestine Vitamins, water, and electrolytes are reclaimed Major function is propulsion of feces toward the anus Colon is not essential for life

30. Copyright © 2010 Pearson Education, Inc. Motility of the Large Intestine Haustral contractions Slow segmenting movements Haustra sequentially contract in response to distension

31. Copyright © 2010 Pearson Education, Inc. Defecation Mass movements force feces into rectum Distension initiates spinal defecation reflex Parasympathetic signals Stimulate contraction of the sigmoid colon and rectum Relax the internal anal sphincter Conscious control allows relaxation of external anal sphincter

32. Copyright © 2010 Pearson Education, Inc. Figure 23.31 Impulses from cerebral cortex (conscious control) Voluntary motor nerve to external anal sphincter External anal sphincter (skeletal muscle) Internal anal sphincter (smooth muscle) Sensory nerve fibers Involuntary motor nerve (parasympathetic division) Stretch receptors in wall Rectum Sigmoid colon 3 1 2 Distension, or stretch, of the rectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons. A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter. If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces may pass.

33. Copyright © 2010 Pearson Education, Inc. VOMITING forcible expulsion of stomach (sometimes duodenum) contents through mouth irritation and stretching of stomach induce vomiting (impulses are sent to medulla oblongata) diaphragm, abdominal muscles and digestive organs play a role

34. Copyright © 2010 Pearson Education, Inc.

36. Vitamin Absorption In small intestine Fat-soluble vitamins (A, D, E, and K) diffuse into absorptive cells Water-soluble vitamins (vitamin C and B vitamins) are absorbed by diffusion or by passive or active transporters. Vitamin B 12 binds with intrinsic factor, and is absorbed by endocytosis

37. Copyright © 2010 Pearson Education, Inc. Vitamin Absorption In large intestine Vitamin K and B vitamins from bacterial metabolism are absorbed

38. Copyright © 2010 Pearson Education, Inc. Electrolyte Absorption Mostly along the length of small intestine Iron and calcium are absorbed in duodenum Na + is coupled with absorption of glucose and amino acids Ionic iron is stored in mucosal cells with ferritin K + diffuses in response to osmotic gradients Ca 2+ absorption is regulated by vitamin D and parathyroid hormone (PTH)

39. Copyright © 2010 Pearson Education, Inc. Water Absorption 95% is absorbed in the small intestine by osmosis Net osmosis occurs whenever a concentration gradient is established by active transport of solutes Water uptake is coupled with solute uptake

40. Copyright © 2010 Pearson Education, Inc. Malabsorption of Nutrients Causes Anything that interferes with delivery of bile or pancreatic juice Damaged intestinal mucosa (e.g., bacterial infection)

41. Copyright © 2010 Pearson Education, Inc. Developmental Aspects In the third week Endoderm has folded and foregut and hindgut have formed Midgut is open and continuous with the yolk sac Mouth and anal openings are nearly formed In the eighth week Accessory organs are budding from endoderm

42. Copyright © 2010 Pearson Education, Inc. Figure 23.35 Stomodeum Foregut Site of liver development Midgut Spinal cord Hindgut Proctodeum Endoderm Brain Oral membrane Heart Yolk sac Cloacal membrane Body stalk (a) Lung bud Liver Gall- bladder Cystic duct Ventral pancreatic bud Dorsal pancreatic bud Duodenum Stomach (b) Bile duct

43. Copyright © 2010 Pearson Education, Inc. Developmental Aspects Fetal nutrition is via the placenta, but the GI tract is stimulated to mature by amniotic fluid swallowed in utero The newborn’s rooting reflex helps the infant find the nipple; the sucking reflex aids in swallowing

44. Copyright © 2010 Pearson Education, Inc. Developmental Aspects During old age GI tract activity declines, absorption is less efficient, and peristalsis is slowed Diverticulosis, fecal incontinence, and cancer of the GI tract

45. Copyright © 2010 Pearson Education, Inc. Cancer Stomach and colon cancers rarely have early signs or symptoms Metastasized colon cancers frequently cause secondary liver cancer Prevention Regular dental and medical examination