1. Pages 874-928 C h a p t e r 24 The Digestive System PowerPoint® Lecture Slides prepared by John L. Wilson Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

2. Digestive Anatomy Overview Mouth and tongue Salivary Glands Pharynx Esophagus Stomach Liver Pancreas Small intestine Large intestine

3. Functions of the Digestive Tract Ingestion – intake of food (eating) Mechanical Digestion – chewing, swallowing, peristalsis and other muscular actions of GI tract Chemical Digestion – chemical break-down of food molecules catalyzed by digestive enzymes Secretion – release of useful chemicals such as enzymes and mucus by cells and glands Absorption – uptake of substances, such as nutrients, into circulation Excretion – elimination of digestive wastes

4. Digestive Enzymes Enzymes are protein catalysts Enzymes are not altered themselves Enzymes speed up chemical reactions, and chemical digestion involves a series of chemical reactions

5. Digestive enzymes are called hydrolytic enzymes. Water is used to split food molecules Digestive Enzymes Continued

6. Digestive Enzymes Enzymes are sensitive to such things as temperature and pH The names of enzymes usually end in “ase” For example, sucrase is the enzyme that catalyzes the hydrolysis of the sugar sucrose

7. Digestion in Mouth Mastication Another name for chewing Breaks-up and lubricates food Swallowing Increases surface area of food so enzymes can work more efficiently

8. Digestion in Mouth Salivary amylase, secreted by salivary glands, digests starch into smaller molecules, the smallest being the disaccharide sugar maltose StarchMaltose amylase

9. Swallowing (Deglutition) – Buccal Phase Tongue pushes bolus of food from oral cavity into oropharynx

10. Swallowing – Pharyngeal Phase Soft palate closes nasopharynx and epiglottis closes glottis

11. Swallowing – Esophageal Phase Peristalsis propels bolus down esophagus toward stomach

12. Swallowing – Esophageal Phase Cardiac (lower esophageal) sphincter opens and bolus enters stomach

13. Stomach Histology Gastric Pit----------------- Gastric Gland------------ Stomach Lumen Muscularis - 3 layers Submucosa with CT, glands and vessels Mucosa – pits with gastric glands Serosa – visceral peritoneum

14. Gastric Glands Gastric glands Mucous neck cells secrete protective mucus Chief cells secrete pepsinogen Parietal cells secrete hydrochloric acid G cells secrete hormone gastrin which stimulates gastric secretions Mucous Neck Cells Parietal Cell Chief Cell G Cell

15. Functions of the Stomach Storage-can eat lots of food at one sitting Limited absorption in stomach Aspirin and some other drugs Alcohol Some water Electrolytes

16. Functions of the Stomach Protection Acid retards bacterial growth Some detoxification of alcohol Chemical digestion Protein digestion begins, but not completed Inactive enzyme pepsinogen secreted by chief cells of gastric glands. Why must it be inactive when secreted?

17. Chemical Digestion Details Pepsinogen is converted to active enzyme pepsin in stomach lumen (cavity) by pepsin and hydrochloric acid (HCl) Pepsin digests proteins to smaller chains of amino acids called peptides Pepsinogen HCl & pepsin Pepsin Protein Peptides

18. Functions of Stomach Mechanical Digestion in Stomach Mixing waves every 15-20 seconds Reduce food to liquid acid chyme Force small amounts of acid chyme from stomach into the small intestine

19. Small Intestine Histology Lined with about 4.5 million villi (villus ) Small finger like extensions Covered with a simple columnar mucous membrane Blood capillaries inside for absorbing most substances Single lymph capillary called a lacteal for absorbing most fat

20. Small Intestine Histology - Villus Blood Capillaries Simple Columnar Cells------- Lacteal – lymph capillary Absorptive Cells – digestion & absorption Goblet Cells – secretes mucus Endocrine Cell – secretes intestinal hormones such as gastrin, cholecystokinin and secretin Intestinal crypt--------

21. Small Intestine Physiology Responsible for most chemical digestion Enzymes from pancreas and small intestine complete digestion of protein, starch, disaccharide sugars and fat Gallbladder empties bile into small intestine to aid in fat digestion Absorbs most substances

22. Small Intestine Physiology Mechanical digestion Peristalsis propels chyme along intestine Segmentation moves chyme back and forth to mix it thoroughly

23. Pancreas Head, neck,body and tail Head into duodenum Tail to spleen Pancreatic duct joins bile duct and connects to duodenum

24. Histology of Pancreas Acini are exocrine cells that secrete digestive enzymes into ducts Ducts secrete bicarbonate to buffer acid chyme from stomach and help to raise its pH from 2-3 to 7-8 Why raise intestinal pH?

25. Secretion of Pancreatic Juices Secreted by acini and ducts About 1 liter secreted per day Contains enzymes to digest protein, starch fat and nucleic acids (DNA, RNA)

26. Digestion by Pancreatic Enzymes Protein Digestion Four proteolytic enzymes secreted as inactive proenzymes. Why? Proenzymes sequentially activated in duodenum (first part of small intestine) These enzymes digest protein and polypeptides to smaller peptides and amino acids

27. Starch digestion Starch not digested by salivary amylase in the mouth and stomach is digested in intestine by pancreatic amylase Digestion same as in mouth Pancreatic Digestion StarchMaltose Pancreatic Amylase

28. Pancreatic Digestion Fat Digestion Bile from the gallbladder prepares fat molecules for chemical digestion Bile flows down bile duct into duodenum to mix with and emulsify the fat What does emulsify mean?

29. Chemical Digestion of Fats (triglycerides) Fat (triglyceride) molecules made of glycerol and three fatty acids) Digested in small intestine by pancreatic lipase Digestion of each triglyceride yields a monoglyceride molecule and two fatty acid molecules Monoglyceride lipase Triglyceride +Two fatty acids

30. Digestion by Intestinal Enzymes Called brush-border enzymes Located in microvilli of intestinal absorptive cells Peptidases Digest peptides to amino acids

31. Intestinal Enzymes Disaccharidases digest disaccharides to monosaccharides Sucrose Glucose + Fructose sucrase Maltose maltase Glucose + Glucose Lactose lactase Glucose + Galactose

32. Absorption in the Small Intestine Absorption is the uptake of substances into absorptive cells then into blood and lymph Villi and microvilli of absorptive cells provide large surface area for absorption Most digested foods, water, electrolytes, vitamins and other substances absorbed in small intestine

33. Absorption into Blood Monosaccharides Amino acids Water Electrolytes such as sodium, potassium. Water soluble vitamins such as vitamin C and the B vitamins

34. Absorption Into Lacteals (lymph) Fat soluble vitamins Fatty acids and monoglycerides Bile salts help with absorption into intestinal cells (micelles) Triglycerides (fat) reformed in intestinal cells Triglycerides combine with protein and are transported to lymph of lacteal (chylomicrons) Triglycerides are then carried by protein to the blood. Where? Lacteal

35. Functions of Large Intestine Feces formation by bacterial action Limited digestion of undigested food by bacteria Formation of vitamin K and some B vitamins by bacteria Absorption of some water, electrolytes, vitamins and bile salts

36. Functions of the Liver Carbohydrate, lipid and protein metabolism Removal of waste products such as bilirubin Storage of glycogen, vitamins and iron Phagocytosis by Kupffer cells Bile secretion Plasma protein synthesis Detoxification of toxins such as alcohol

37. Bile One-half liter to a liter of bile each day Functions of bile Emulsification of fat in small intestine Excretion of bilirubin and cholesterol Aid in fat absorption

38. Medical Terms Gingivitis-inflammation of gums Periodontal disease – plaque causes destruction of periodontal membrane and jaw bone with possible loss of teeth Stomatitis – inflammation of mouth Dental caries - cavities

39. Medical Terms Esophagitis and GERDS – acid reflux from stomach into esophagus Gastritis – inflammation of stomach GI neoplasms – cancers of GI tract Hepatitis – inflammation of liver, several types Peptic ulcer – erosion of stomach/duodenal lining, usually caused by a bacterium

40. Acid Blocking Drugs* Histamine (H 2 ) blockers Tagamet Zantac Pepcid AC Proton pump blockers Prilosec Nexium Prevacid