What is the function of your Digestive System?

1. What is the function of your Digestive System?

2. Figure 23.1

3. Digestive System Brainstorm what each of the following organs/structures does regarding digestion: • The alimentary canal or gastrointestinal (GI) tract digests and absorbs food • Alimentary canal consists of – mouth, pharynx, esophagus, stomach, small intestine, and large intestine • Accessory digestive organs – teeth, tongue, salivary glands, liver, gallbladder and pancreas

4. Digestive Process • The GI tract is a “disassembly” line • Nutrients become more available to the body in each step (example: proteins broken into amino acids) • There are six essential activities: 1. Ingestion 2. propulsion by peristalsis 3. mechanical digestion 4. Chemical digestion 5. absorption 6. defecation

5. Figure 23.2

6. Peritoneum and Peritoneal Cavity • Peritoneum – serous (moist) membrane of the abdominal cavity

7. Peritoneal Cavity • Mesentery – double layer of peritoneum (connective tissue) that provides: • Vascular and nerve supplies to the viscera (organs) • Hold digestive organs in place and store fat

8. Histology of the Alimentary Canal Figure 23.6

9. Oral Cavity and Pharynx: Anterior View Figure 23.7b

10. Salivary Glands Figure 23.9a

11. Salivary Glands • Produce and secrete saliva that: 1. Cleanses the mouth 2. Moistens and dissolves food chemicals 3. Aids in bolus formation 4. Contains digestive enzymes that break down starch (sugar)

12. Digestive Processes in the Mouth • Food is ingested • Mechanical digestion begins (chewing) • Propulsion is initiated by swallowing • The pharynx and esophagus serve as conduits to pass food from the mouth to the stomach

13. Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Esophagus Trachea Bolus (a) (b) Upper esophageal sphincter contracted Upper esophageal sphincter relaxed (c) Upper esophageal sphincter contracted Relaxed muscles Relaxed muscles Circular muscles contract, constricting passageway and pushing bolus down Gastroesophageal sphincter open Bolus of food Longitudinal muscles contract, shortening passageway ahead of bolus Stomach Gastroesophageal sphincter closed (e) (d) Figure 23.13

14. Figure 23.14a

15. Microscopic Anatomy of the Stomach • Epithelial (tissue) lining is composed of: • Goblet cells that produce a coat of alkaline mucus • Gastric pits contain gastric glands that secrete gastric juice (acidic) and mucus

16. Microscopic Anatomy of the Stomach Figure 23.15a

17. Did You Know That?Your stomach acid is so strong that you grow a new stomach lining every three days? • You can eat standing on your head, because your esophagus pushes food into your stomach, evenuphill? • Your body makes about one liter of saliva every day?

18. Digestion in the Stomach • The stomach: • Holds ingested food • Degrades this food both physically and chemically • Delivers chyme to the small intestine • Enzymatically digests proteins with pepsin

20. Small Intestine: Gross Anatomy • Has three subdivisions: duodenum, jejunum, and ileum • Structural modifications increase surface area: • Villi • Microvilli

21. Small Intestine: Microscopic Anatomy Figure 23.21

22. Functions of Small Intestine: 1) Chemical digestion & 2) Absorption of nutrients into blood • Intestinal juice secreted by intestinal glands in response to distension (food entering the area) • Slightly alkaline and isotonic with blood plasma • The majority of chemical digestion occurs in the duodenum • Absorption occurs in the jejunum & ileum

23. Duodenum linked to Pancreas, Gallbladder & Liver Figure 23.20

25. Liver (largest organ in body) & Gallbladder • Bile is produced in the liver and the Gallbladder stores bile

26. Gallbladder and Associated Ducts Figure 23.20

27. Composition of Bile • A yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes • Bile salts are cholesterol derivatives that: • Emulsify fat • Facilitate fat and cholesterol absorption • Help solubilize cholesterol

28. Pancreas • Location • Lies deep to the greater curvature of the stomach • The head is encircled by the duodenum and the tail abuts the spleen

29. Pancreas • Exocrine function • Secretes pancreatic juice which breaks down all categories of foodstuff • The pancreas also has an endocrine function – release of insulin and glucagon (hormones)

30. Pancreatic Activation Figure 23.27

31. Digestion in the Small Intestine • As chyme enters the duodenum: • Carbohydrates and proteins are only partially digested • No fat digestion has taken place

32. Digestion in the Small Intestine • Digestion continues in the small intestine • Chyme is released slowly into the duodenum • Secretions from the Gallbladder and Pancreas aid in the breakdown of chyme (Duodenum) • Virtually all nutrient absorption takes place in the small intestine

33. Motility in the Small Intestine • After nutrients have been absorbed: • Peristalsis begins with each wave starting distal to the previous • Meal remnants, bacteria, mucosal cells, and debris are moved into the large intestine

34. Large Intestine • Has three unique features: 1. three bands of smooth muscle 2. pocketlike sacs 3. fat-filled pouches

35. Large Intestine • Is subdivided into the cecum, appendix, colon, rectum, and anal canal • The saclike cecum: • Lies below the ileocecal valve • Contains a wormlike vermiform appendix

36. Large Intestine Figure 23.29a

37. Valves and Sphincters of the Rectum and Anus • Three valves of the rectum stop feces from being passed with gas • The anus has two sphincters: • Internal anal sphincter composed of smooth muscle • External anal sphincter composed of skeletal muscle • These sphincters are closed except during defecation

38. Bacterial Flora • The bacterial flora of the large intestine consist of: • Bacteria surviving the small intestine that enter the cecum and • Those entering via the anus • These bacteria: • Colonize the colon • Ferment indigestible carbohydrates • Release irritating acids and gases (flatus) • Synthesize B complex vitamins and vitamin K

39. Functions of the Large Intestine • no further digestion takes place 1. Vitamins, water, and electrolytes are reabsorbed 2. Its major function is propulsion of fecal material toward the anus • Though essential for comfort, the colon is not essential for life

40. Defecation • Distension of rectal walls caused by feces: • Stimulates contraction of the rectal walls • Relaxes the internal anal sphincter • Voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs

41. Developmental Aspects • Digestive system has few problems until the onset of old age • During old age the GI tract activity declines, absorption is less efficient, and peristalsis is slowed

42. Cancer • Stomach and colon cancers rarely have early signs or symptoms • Metastasized colon cancers frequently cause secondary liver cancer

43. Cancer • Colon cancer is the 2nd largest cause of cancer deaths in males (lung cancer is 1st) • Forms from benign mucosal tumors called polyps whose formation increases with age • Regular colon examination should be done for all those over 50

45. http://www.mic.stacken.kth.se/Diseases/C06.html