DIGESTIVE SYSTEM

1. DIGESTIVE SYSTEM Alimentary Canal and Accessory Organs

2. 2 main parts to the digestive system: • Alimentary canal • Performs most digestive functions • Long “tube” from mouth to anus • Accessory organs • Assist the digestive process in various ways. Digestive System

3. ALIMENTARY CANAL(GI Tract) Digestive System- Ch. 14

4. Aka: Gastrointestinal Tract (GI Tract) • Continuous, hollow, coiled muscular tube running from the mouth to the anus. • Open at both ends. • Organs include: Alimentary Canal

5. Alimentary Canal/GI Tract

6. Mucous membrane lined cavity where food enters digestive tract. • As food enters the mouth, it is mixed with saliva and masticated (chewed)- mechanical digestion! • Food breakdown begins here. Mouth

7. Food passageway for food, air, and fluids. • Nasopharynx goes on to the respiratory tract. • Oropharynxand laryngopharynx continue on to the digestive tract via the esophagus. Pharynx

8. Runs from pharynx to stomach • Very similar composition to the rest of the alimentary canal (the intestines) • 4 Tissue Layers • Mucosa • Innermost layer- moist membrane • Submucosa • Just outside of mucosa • Connective tissue containing blood vessels, nerves, and lymph nodes • Muscularisexterna • Inner circular layers of muscle and outter longitudinal layer of muscle • Serosa • Outermost layer- single layer of serous fluid producing cells- the VISCERAL PERITONEUM. Esophagus

9. The alimentary canal wall consists of 2 major nerve plexuses (systems of nerves): • Submucosal nerve plexus • Myenteric nerve plexus • These help regulate the movement of food and secretory activity of the GI tract. • See page 436 figure 14.3 for a visual! GI Tract Wall, continued

10. Up to 1 gallon of food can be contained in the stomach at one time. • When it is empty is collapses in on itself- due to deep folds called rugae. • 3 layers of muscle- circular, longitudinal, and oblique- work to churn, mix, and move food along. (Mechanical digestion!) Stomach

11. Chemical digestion of protein begins here. (Chemical digestion of carbs began in the mouth with salivary amylase!) • Pepsinogen enzymes (produced by chief cells) activated by HCl(produced by parietal cells). • A thick mucus layer protects the stomach itself from the acids and enzymes. • Most digestion occurs in the PYLORIC region of the stomach. Stomach, continued

12. Stomach, continued

13. Chyme (what was our food!) leaves the stomach/enters the small intestine via the pyloric sphincter. • The body’s MAJOR digestive organ- primarily chemical digestion. • Food is finally prepared to enter the bloodstream for transport to the rest of the body. • Duodenum, Jejunum, and Ileum Small Intestine

14. Bile (from the liver), intestinal enzymes and pancreatic enzymes work to digest food. • Surface area is increased with microvilli (“brush border”), villi, and circular folds (“plicaecirculares”)- this allows digestion of more nutrients at once. • Lymphatic Peyer’s Patches prevent bacteria from growing in undigested food. Small Intestine, continued

15. Pyloric sphincter pancreas

17. Remaining undigested food exits the SI/enters the LI via the ileocecal valve. • Primary function is to recover (take back into our body) as much water as possible from indigestible food before excreting it as feces. • Cecum, appendix, colon, rectum, and anal canal. • No villi are necessary here since no nutrient absorption occurs in the large intestine. • GOBLET CELLS produce mucus to ease the passage of feces. Gross! Large Intestine

18. We will cover accessory organs tomorrow! • Complete #2, 5, p.245 A (the stomach picture), 13, 14, and 15 in your packet! All done for today!

19. ACCESSORY ORGANS Digestive System- Ch. 14

20. Organs include: ACCESSORY ORGANS

21. 3 pairs of salivary glands secrete into the mouth: • Parotid glands • Inflammation = mumps! • In front of the ears • Submandibular glands • Sublingual glands Salivary Glands

22. Secrete saliva (mucus and serous fluids mixture) into the floor of the mouth. • Mucus helps bind the food into a BOLUS (a mass of food- easier to chew and swallow). • Serous portion contains SALIVARY AMYLASE • Begins breakdown of starch/carbs Submandibular and Sublingual Glands

23. Saliva also protects against bacterial infections. • Contains lysozyme and anitbodies (IgA) • Dissolves food chemicals into a solution so they can be tasted by our taste buds. Saliva continued

24. Teeth are for mastication, or chewing- mechanical digestion. • The rest is pretty boring, so we’re skipping it….  Teeth

25. Pancreatic enzymes breakdown all categories of food. • These are secreted into the DUODENUM in an alkaline (basic) solution that neutralizes that stomach acid entering from the pyloric sphincter. • The pancreas also produces insulin and glucagon- hormones aiding in nutrient absorption. Pancreas

26. Protease- breaks down proteins • Lipase- breaks down fats • Amylase- more starch/carb breakdown • Bicarbonate- the basic solution neutralized the stomach acid Pancreatic Enzymes

27. Insulin: released in response to HIGH blood sugar- aids glucose entry INTO cells (and out of blood stream). • Glucagon: released in response to LOW blood sugar- aids in RELEASE of glucose OUT of cells (and into blood stream). Pancreatic Hormones

29. Liver is the largest gland in the body. • Many manyMANY metabolic and regulatory roles. • Its digestive function is to produce BILE. • Released into the DUODENUM via the Hepatic Duct. • Solution containing bile salts, bilirubin, cholesterol, phospholipids, and electrolytes. • EMULSIFIES fats (breaks down larger globules into smaller ones) to quicken digestion by lipases (fat digesting enzymes). Liver

30. Small green sac on the bottom of the liver. • Stores bile when it is not needed for digestion. • Water is lost from the bile as it sits in the gallbladder- if it sits too long GALLSTONES form. Ouch! Gallbladder

31. Doudenum

32. That is it for accessory organs for now!  • Complete #2, 4, 5, 14, 15, 16 (not covered but related!) for the rest of the period. Tomorrow is Friday! 