Chapter 8

1. Chapter 8 Digestive System and Nutrition

2. Outline • Overview of Digestion • The First Part of the Digestive Tract • The Stomach and Small Intestine • Three Accessory Organs and Regulation of Secretions • The Large Intestine and Defecation • Nutrition and Weight Control (Should reviewCh.2, Molecules of Life, pp. 22-30)

3. Overview of Digestion • Also called the alimentary tract, gastrointestinal tract (G.I. tract), “gut”. • From the mouth to the anus. • There are two types of digestive processes: • 1. Mechanical. . . . • 2. Chemical. . . . • Digestion of food is an extracellular process due to enzymes secreted into the gut by glands that reside in the lining or lie nearby.

4. Overview of Digestion • Functions of this system include: • Ingest food. • Digest it into small molecules that can cross the cell membrane. • Movement of contents along tract. • Absorb nutrient molecules. • Eliminate nondigestible wastes.

7. The Wall of the Digestive Tract • Layers from inside, out: (MSMS) • Mucosa - Mucus membrane layer. • Submucosa - Submucosal layer. • Muscularis – Longitudinal and circular smooth muscle layer. • Serosa - Serous membrane layer. • Disorders: • Diverticulosis, diverticulitis, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), appendicitis, peritonitis.

9. The Digestive TractMouth : “Food Receiver” • Functions: ingest, break down (mechanical), begin digestion (chemical), taste, form into bolus for swallowing. • Roof of the mouth composed of two parts. • Anterior (front) hard palate. • Posterior (back) soft palate. • Tonsils help protect against infection. • Three pairs of salivary glands (exocrine glands) send juices through ducts to the mouth. • Saliva contains digestive enzymes (bicarbonate and salivary amylase).

10. The Digestive TractMouth : “Food Receiver” • Teeth used to chew food into pieces small enough to swallow. • Each tooth has two main divisions. • Crown. • Root. • Tongue mixes chewed food with saliva and forms a bolus in preparation for swallowing.

12. The Pharynx : “A Crossroad” • The pharynx (throat) receives air from the nasal cavities and food from the mouth. • Swallowing is a reflex action that occurs in the pharynx. • Soft palate moves to close off nasopharynx, and the trachea moves under the epiglottis to cover the glottis.

13. Swallowing

14. The Esophagus : “A Food Conductor” • Function? • The esophagus is a muscular tube that passes from the pharynx through the thoracic cavity and diaphragm into the abdominal cavity. • Rhythmic peristalsis pushes food along the digestive tract. • Sphincters encircle tubes and act as valves. • Heartburn vs. Acid reflux disease ( gastroesophageal reflux disease, GERD)

16. HEALTH FOCUS Heartburn (GERD)

17. The Stomach : “Food Storer and Grinder” • Functions: stores food, mixes food (mechanical), kills bacteria, and aids in digestion (chemical). • Columnar epithelial lining contains gastric pits leading into gastric glands. • Produce gastric juice containing HCl (pH ~2) and enzyme pepsin. • Walls of stomach have folds which help churn and mix food and gastric juices. • Chyme leaves the stomach and enters the small intestine.

18. The Stomach : “Food Storer and Grinder” • Ulcers? • Form when HCl penetrates mucus barrier and disintegrates tissue. • Called a peptic ulcer. • However, recently discovered that may be caused by bacteria (Helicobacter pylori ) that inhibit mucus production! • What is the significance of this discovery? • William Beaumont and Alexis St. Martin !?

19. HISTORICAL FOCUS A Window to the Stomach: Alexis St. Martin and Dr. William Beaumont

22. The Small Intestine : “Food Processor” • Functions: • Receives secretions from liver, pancreas. • Mechanical, chemical digestion of food. • Absorption of nutrients. • Transports undigested material to large intestine. • Thus, is the primary site for chemical breakdown of food and nutrient absorption. • ~ 1 inch wide, ~ 18 feet long (6 meters).

23. The Small Intestine : “Food Processor” • The duodenum (first ~10”) is where the chemical breakdown of food gets under way. • Receives bile from liver (gall bladder) to “emulsify” fat. • Receives digestive enzymes and sodiumbicarbonate from the pancreas for chemical breakdown of food and to neutralize the chyme. • Duodenal ulcers? • Along the small intestine are the villi (s. villus) – the structural unit of the small intestine.

24. The Small Intestine : “Food Processor” • Are covered by microvilli to increase the surface area for absorption of nutrients. • Surface area ~ that of NFL football field!!! • Blood vessels absorb sugars (from CHO) and amino acids (from proteins). • Lacteal – small lymph vessels which absorb “fats” and transport / return them and fluids to the blood stream. • Lactose intolerance? • Link between obesity, type 2 diabetes, and cardiovascular disease?

27. Three Accessory Organs • Pancreas • Exocrine part produces digestive enzymes • Endocrine part secretes insulin and glucagon that regulate blood glucose levels. • Liver maintains homeostasis by. . . . • Produces bile (from breakdown of RBC’s). • Detoxifies blood. • Stores iron, fat-soluble vitamins: A, D, E, K • Maintains blood glucose levels (< 0.1%) • Produces urea. • Makes blood proteins (clotting, etc.) • Helps regulate blood cholesterol level (bile salts)

28. Three Accessory Organs • Liver disorders: • Jaundice. • Hemolytic - RBC broken down. • Obstructive - bile duct blocked due to gallstones. • Hepatitis – viral infection causing inflammation. • Cirrhosis. • Common among alcoholics. • Liver becomes fatty and tissue is replaced by inactive fibrous scar tissue . . . . liver cancer! • Gallbaldder stores excess bile. . . . Gallstones?

29. Regulation of Digestive Secretions • Secretion of digestive juices is promoted by the nervous system and by hormones. • Hormones are produced by one set of cells and affect a different set of cells. • Gastrin. • Gastric inhibitory peptide (GIP). • Secretin. • Cholecystokinin (CCK).

30. Hormonal Control of Digestive Secretions

31. Hepatic Portal Circuit

32. The Large Intestine : “H2O, salt Processor” • Functions: • Absorbs water and salts. • Prepares and stores nondigestible material until “defecation”. • Absorbs vitamins produced from bacterium E. coli. • Is ~ 2 ½ in. wide, ~ 5 feet long. • Parts: • Cecum is blind end of large intestine below entrance from small intestine. • Contains the vermiform (“worm-like”) appendix – plays role in immunity.

34. The Large Intestine : “H2O, salt Processor” • Appendicitis?  peritonitis? • Colon. • Ascending, transverse, descending, sigmoid. • May develop polyps – small growths arising from the epithelial lining. • May be benign or malignant. • May increase likelihood of colon cancer. • Can be removed surgically. • Risk reduced by eating a low-fat, high-fiber diet.

35. The Large Intestine : “H2O, salt Processor” • Rectum. • Muscular, last 8 inches. • Anus: “defecation” of “feces”. • Diarrhea is caused by infection of the lower intestinal tract and nervous stimulation, and results in increased peristalsis – too much water. . . . • Dehydration. • Constipation can be caused by a lack of H2O and fiber, and leads to dry, hard feces. . . . • Hemorrhoids (“piles”). • Laxatives!?

36. Disorders of the Colon and Rectum - continued • Hemorrhoids (“piles”) ? • Diverticulosis ? • Irritable Bowel Syndrome (IBS) • or spastic colon ? • Inflammatory Bowel Disease (IBD) or colitis ? • Polyps and cancer ?

37. HEALTH FOCUS Swallowing a Camera

38. Digestive Enzymes / Nutrition • Dehydration synthesis – “building”, (+). • also called condensation reaction. • Hydrolysis – “tearing down”, (-). • Prefixes: mono- = one, single / di- = two / poly- = many (> 3). • Words for Food Components: • peptide = protein (from peptide bond). • saccharide = sugar (from latin for sugar). • glyceride = lipids (fats, oils, etc.).

39. Digestive Enzymes • Digestive enzymes are hydrolytic enzymes that break down substances into nutrient molecules. • Glucose and amino acids are absorbed into blood capillaries of the villi. • Fatty acids and glycerol reform within epithelial cells and enter lacteals as lipoprotein droplets.

40. Digestive Enzymes • Are proteins. • Are specific. • Have a preferred pH. • Have a preferred temperature. • Are found (produced and released) in specific places: • Mouth. • Stomach. • Duodenum (pancreatic juice, epithelial cells of villus).

41. Nutrition and Weight Control

42. Classes of Nutrients • Nutrition? • Involves interaction between “food” and the organism. • Food is an organic, energy containing substance. • Nutrient is a substance found in food that is used by the body to maintain health. • Balanced diet is obtained by eating a variety of food from four food groups. • Represented by the Food Guide Pyramid, old followed by the new.

45. Food Components • The body requires three major classes of micronutrients to supply energy and optimum cellular metabolism. • Carbohydrates. • Protein. • Fat. • In addition, the body requires. • Vitamins. • Minerals. • Human diet has changed substantially with the development of civilization. . . .

47. Food Components - Carbohydrates • Carbohydrates (CHO) are digested to simple sugars, which are, or can be, converted to glucose. • Quickest, most readily absorbed source of energy for the body. • Complex CHO (breads, cereals) should make up the bulk of the diet, not simple sugars (candy, “sweets”, soft drinks). • Simple sugars are labeled “empty calories” because. . ? Glycemic index (GI) • Blood glucose is kept at ~0.1% by breakdown of glycogen or conversion of amino acids.

50. Food Components - Proteins • Found in meat, fish, poultry, dairy products, legumes, nuts, cereals. • Incorporated into structural proteins in muscles, skin, hair, nails. • Foods richest in protein are apt to be richest in fat! • Adequate protein formation requires twenty different amino acids, including 8 (adult), 9 (children) essential amino acids. • Body is unable to produce essential amino acids. • Complete protein contains all essential amino acids. • Amino acids are not stored in the body, and thus a daily supply is needed.