The Digestive System

1. 29 The Digestive System

2. Learning Outcomes 29.1 List the functions of the digestive system. 29.2 Trace the pathway of food through the alimentary canal. 29.3 Describe the structure and functions of the mouth, teeth, tongue, and salivary glands. 29.4 Describe the structure and function of the pharynx.

3. Learning Outcomes (cont.) 29.5 Describe the swallowing process. 29.6 Describe the structure of the esophagus and tell how it propels food into the stomach. 29.7 Describe the structure and functions of the stomach. 29.8 List the substances secreted by the stomach and give their functions.

4. Learning Outcomes (cont.) 29.9 Describe the structure and functions of the small intestine. 29.10 List the substances secreted by the small intestine and describe the importance of each. 29.11 Describe the structure and functions of the large intestine, including the anal canal and rectum. 29.12 Explain the structures and functions of the liver, gallbladder, and pancreas.

5. Learning Outcomes (cont.) 29.13 List the substances released by the liver, gallbladder, and pancreas into the small intestine and give the function of each secretion. 29.14 Tell what types of nutrients are absorbed by the digestive system and where they are absorbed. 29.15 Describe the causes, signs and symptoms, and treatments of various diseases and disorders of the digestive system.

6. Introduction • Digestion • Mechanical and chemical breakdown of foods into forms that body cells can absorb • The organs of the digestive system carry out digestion • Two categories • Alimentary canal organs • Accessory organs

7. Alimentary Canal • Wall of alimentary canal • Mucosa • Innermost layer; epithelial tissue • Secretes enzymes and mucus into lumen • Absorbs nutrients • Submucosa • Inferior to mucosa; loose connective tissue, blood vessels, glands, and nerves • Blood vessels carry away absorbed nutrients • Muscular layer • Just outside submucosa; layers of smooth muscle • Contracts to move materials through the canal

8. Alimentary Canal(cont.) • Serosa • Double-walled outermost layer: peritoneum • Visceral peritoneum • Innermost wall of serosa • Secretes serous fluid to keep outside of canal moist • Parietal peritoneum • Abdominal lining • Movements • Churning – mixes substances in the canal • Peristalsis – propels substances through the tract

9. Apply Your Knowledge What are the layers of the wall of the alimentary canal and what do they do? ANSWER: The layers are: Mucosa: innermost layer; secretes enzymes and mucus into the canal and absorbs nutrients Submucosa: inferior to the mucosa; carries away absorbed nutrients Muscular layer: just outside the submucosa; contracts to move materials through the canal Serosa: double-walled outer layer; secretes serous fluid to keep outside of canal moist Bravo!

10. The Mouth • Buccal cavity • Mechanical digestion • Takes in food and reduces its size by chewing • Starts chemical digestion • Saliva contains the enzyme amylase, which breaks down carbohydrates

11. The Mouth (cont.) • Cheeks hold food in mouth • Lips – sensory nerve fibers that judge temperature of food • Tongue • Skeletal muscles covered by mucous membrane • Lingual frenulum – holds tongue to floor of mouth • Mixes food, holds food between teeth, contains taste buds • Lingual tonsils– lymphatic tissue destroys bacteria and viruses on back of tongue

12. The Mouth (cont.) • Palate • Roof of mouth • Separates oral cavity from nasal cavity • Uvula – portion of soft palate that hangs down in throat • Lymph tissue • Palatine tonsils(oropharynx) • Pharyngeal tonsils – adenoids (nasopharynx)

13. Teeth – decrease size of food particles Incisors– bite off food pieces Cuspids – tear tough food Bicuspids and molars – grind food Salivary glands Cells Serous Mucous Glands Parotid Submandibular Sublingual The Mouth (cont.)

14. Apply Your Knowledge Matching: ___ Buccal cavity A. Saliva ___ Roof of mouth B. Mouth ___ Grind food C. Bolus ___ Adenoids D. Palate ___ Water, enzymes, and mucus E. Bicuspids ___ Mass of food mixed with saliva and mucus F. Pharyngeal gland ANSWER: B D Very Good! E F A B

15. Throat Functions Connects nasal cavity with oral cavity for breathing Pushes food into esophagus Divisions Nasopharynx Behind nasal cavity Oropharynx Behind oral cavity Laryngopharynx Behind larynx Continues as esophagus Pharynx

16. Pharynx (cont.) • Swallowing – automatic process • Soft palate rises, uvula covers opening between nasal and oral cavity • Epiglottis covers larynx, keeping food out of it • Tongue presses against roof of mouth, forcing food into oropharynx

17. Pharynx (cont.) • Muscles in pharynx contract, moving food toward esophagus • Esophagus opens • Food is pushed into esophagus by muscles of pharynx

18. The Esophagus • Muscular tube connecting pharynx to stomach • Esophageal hiatus– hole in diaphragm through which esophagus passes • Cardiac sphincter • Circular band of muscle at the opening of the stomach • controls movement of food into stomach

19. Apply Your Knowledge Matching: ___ Connects nasal cavity with oral cavity A. Cardiac sphincter ___ Covers the opening of larynx B. Esophageal hiatus ___ Hole in diaphragm C. Sphincter ___ Controls movement of food into stomach D. Epiglottis ___ Circular bands of muscle E. Pharynx ANSWER: E D B A C CORRECT!

20. Below the diaphragm in the upper left quadrant of the abdominal cavity Functions Receive food from esophagus Mix bolus with gastric juice Start protein digestion Move food into small intestine Sections Cardiac region Fundus Body Pylorus Pyloric sphincter Controls movement of substances into small intestine Stomach The Stomach

21. Stomach The Stomach (cont.) • Lining of stomach • Rugae– folds of the inner lining • Gastric glands • Mucous cells– secrete mucus to protect the lining • Chief cells – secrete pepsinogenpepsin, which digests protein • Parietal cells • Hydrochloric acid needed to convert pepsinogen to pepsin • Intrinsic factorneeded for vitamin B12 absorption

22. The Stomach (cont.) • Gastric glands stimulated by • Parasympathetic nervous system • Gastrin (hormone) • Cholesystokinin (hormone) secreted by the small intestine inhibits gastric glands • Stomach absorbs alcohol, water, and some fat-soluble drugs • Chyme – mixture of food and gastric juices

23. Apply Your Knowledge What are the functions of the stomach? ANSWER: The stomach’s functions are to receive the bolus of food, mix it with gastric juice, start protein digestion, and move food into the small intestine. It also absorbs alcohol, water, and some drugs. Right Answer!

24. Tubular organ extending from the stomach to the large intestine Functions Digestion Absorption of nutrients Duodenum C-shaped Short Jejunum Coiled Majority of small intestine Small Intestine The Small Intestine

25. Small Intestine The Small Intestine (cont.) • Ileum – attached to large intestine • Mesentery • Fan-like tissue that holds jejunum and ileum in the abdominal cavity • Attaches to the posterior wall of the abdomen • Ileocecal sphincter • Controls movement of chyme from the ileum to the cecumof the large intestine

26. The Small Intestine (cont.) • Lining of small intestine • Microvilli – increase surface area • Intestinal glands • Mucus and water • Enzymes • Peptidases– digest proteins • Sucrase, maltase, and lactase– digest sugars • Intestinal lipase – digests fats • Primary controls • Parasympathetic nervous system • Stretching of intestinal wall

27. Apply Your Knowledge Your patient states that she is lactose intolerant. What does that mean? ANSWER: She cannot produce lactase and cannot digest lactose, which is the sugar in dairy products. Nice Job!

28. Large Intestine The Large Intestine • Extends from the ileum to the anus • Cecum • Beginning of large intestine • Veriform appendix • Ascending colon • Portion that goes up the right side of the abdominal cavity

29. Large Intestine The Large Intestine(cont.) • Transverse colon– crosses abdominal cavity from right to left • Descending colon– down left side of abdominal cavity • Sigmoid colon – S-shaped portion in pelvic cavity • Absorbs water and electrolytes

30. Large Intestine The Rectum and Anal Canal • Rectum– off sigmoid colon • Anal canal • Last few centimeters of rectum • Opening to outside of body is the anus

31. The Rectum and Anal Canal (cont.) • Feces • Leftover chyme • Consists of undigested solid materials, little water, ions, mucus, cells of intestinal lining, and bacteria • Defecation reflex • Triggered by periodic contractions of large intestine • Allows anal sphincters to relax

32. Apply Your Knowledge Super! Matching: ___ Vermiform appendix A. Feces ___ Crosses the abdomen B. Ascending colon ___ Up right side of abdomen C. Anal canal ___ S-shaped tube D. Defecation reflex ___ Down left side of abdomen E. Sigmoid ___ Leftover chyme F. Transverse colon ___ Last section of rectum G. Cecum ___ Allows anal sphincters to relax H. Descending colon ANSWER: G F B E H A C D

33. The Liver • Lobular organ in right upper quadrant • Large right lobe and smaller left lobe • Hepatic lobules– contain macrophages • Hepatocytes – process nutrients in blood and make bile • Part of liver’s function • Store vitamins and iron

34. The Liver (cont.) • Hepatic portal vein– carries blood from digestive organs to hepatic lobules • Hepatic duct– bile from liver • Hepatic duct merges with cystic duct from gallbladder and forms common bile duct • Common bile duct– delivers bile to duodenum

35. The Gallbladder • Small sac-like structure located beneath the liver • Only function is to store bile • Cholecystokinin causes the gallbladder to release bile Gallbladder

36. Apply Your Knowledge What is the route of bile through the liver and gallbladder? ANSWER: Bile is made in the hepatocytes and leaves the liver through the hepatic duct. The hepatic duct merges with the cystic duct from the gallbladder to form the common bile duct, which delivers bile to the duodenum. Excellent!

37. Pancreatic amylase– digests carbohydrates Pancreatic lipase– digests lipids Nucleases – digest nucleic acids The Pancreas • Located behind the stomach • Acinar cellsproduce pancreatic juice, which contains these enzymes: • Trypsin, chymotrypsin, and carboxypeptidase– digest proteins

38. Also secretes bicarbonate ions into duodenum Neutralize acidic chyme Enzyme release stimulated by Parasympathetic nervous system Hormones secretin and cholecystokinin (from small intestine) The Pancreas (cont.)

39. Apply Your Knowledge What are the pancreatic enzymes and what do they do? • ANSWER: They are: • Pancreatic amylase – digests carbohydrates • Pancreatic lipase – digests lipids • Nucleases – digest nucleic acids • Trypsin, chymotrypsin, and carboxypeptidase – digest proteins Good Job!

40. The Absorption of Nutrients • Nutrients are necessary food substances • Carbohydrates • Proteins • Lipids • Vitamins • Minerals • Water

41. The Absorption of Nutrients (cont.) • Carbohydrates – provide energy • Polysaccharides– starches • Monosaccharides and disaccharides–simple sugars • Cellulose– provides fiber or bulk • Lipids – used for energy when glucose levels are low • Triglycerides • Cholesterol – essential for cell growth and function

42. The Absorption of Nutrients (cont.) • Protein – used for growth and repair of tissue • Essential amino acids body cannot make • Vitamins • Fat-soluble • Water-soluble • Minerals – used to make enzymes, cell membranes, and proteins

43. ANSWER: T Apply Your Knowledge True or False: ___ Carbohydrates are starches, simple sugars, and cellulose. ___ Excess glucose is stored in the gallbladder as glycogen. ___ Triglycerides are the least abundant lipids ___ Linoleic acid is an essential fatty acid. ___ A, D, E and K are water-soluble vitamins. ___ Minerals are used by cells to make enzymes. liver F most F T Impressive! fat-soluble F T

44. Decreased motility – GERD Decreased absorption More likely to develop ulcers and cancers Decreased ability to detoxify blood Sense of taste altered Dietary changes due to Isolation Depression Aging and the Digestive System

45. Common Diseases and Disorders

46. Common Diseases and Disorders(cont.)

47. Common Diseases and Disorders(cont.)

48. Common Diseases and Disorders(cont.)

49. Common Diseases and Disorders (cont.)

50. Apply Your Knowledge ANSWER: E Matching: ___ Inflammation of the large intestine A. Heartburn ___ Inflammatory bowel disease B. Hemorrhoids ___ Watery and frequent feces C. Constipation ___ Difficult defecation D. Crohn’s disease ___ Inflammation of the stomach lining E. Colitis ___ Inflammation of pouches in the intestinal wall F. Diarrhea ___ GERD G. Gastritis ___ Varicose veins of rectum H. Diverticulitis D F C G H A B Nice Job!