1. Chapter 18 Digestive System

2. Objective • Describe the general function of the digestive system • List the structures and the functions of the digestive system • Describe the action of the enzymes on carbohydrates, fats and protein • Trace food from the beginning of the digestive process to the end • Describe common disorders of the digestive system • Define the key words that relate to this chapter

3. Digestive System • Food must be converted by physical and chemical changes before it can be used by the cells; this process is called digestion • Enzymes • Chemical substances that promote chemical reactions in living things • Alimentary canal • Accessory organs

4. Layers of the Digestive System • Mucosa • Innermost lining • Submucosa • Circular muscle • Longitudinal muscle

5. Lining of the Digestive System • Peritoneum • Two-layered membrane • Parietal (lines the abdominal cavity) • Visceral (covers the outside of each organ in the abdominal cavity • Specialized layers • Mesentery (attaches to the posterior wall of the abdominal cavity and the small intestines) • Greater omentum (contains large amounts of fat and hangs over the abdominal organs like a protective apron)

6. Functions of the Digestive System • Break down food physically • Change food chemically • Absorb the nutrients • Eliminate the waste products of digestion

7. Organs of Digestion • Mouth (oral or buccal cavity) • Functions • Receive food by ingestion • Break food into small particles by mastication • Mix food with saliva • Tongue/accessory organ of digestion • The tongue and its muscles are attached to the floor of the mouth, helping in both chewing and swallowing • Salivary glands • Functions of saliva • Cleansing action on the teeth • Moistens and lubricates food during mastication and swallowing • Dissolves certain molecules so that foods can be tasted • Begins the chemical digestion of starches

8. Teeth/AccessoryOrgan of Digestion • Gingivae or gums • Support and protect the teeth • Teeth • Food chewed or masticated • Deciduous and permanent teeth

9. Esophagus • Muscular tube to transport swallowed food to stomach • Muscles in the upper third are voluntary and lower portion is smooth muscle, or involuntary

10. Stomach • Divided into 3 portions • Fundus (upper part) • Body or great curvature (middle section) • Pylorus (lower portion) • Sphincters • Cardiac sphincter • Pyloric sphincter • Four layers of the stomach wall

11. Gastric Juices • Enteroendocrine glands • Secrete gastrin • Parietal cells • Produce HCL and intrinsic factor • Chief type cells • Produce pepsinogen • Mucus cells • Secrete alkaline mucus

12. Small Intestine • About 20 feet long • Same four layers as the stomach • Divided into 3 sections • Duodenum • Jejunum • Ileum • Functions • Finishes the process of digestion • Absorbs the nutrients • Passes the residue on to the large intestine

13. Digestive Juices inthe Small Intestine • Enzymes, secretin, and cholecystokinin • Pancreatic juices • Protease or trypsin • Amylase or amylopsin • Lipase or steapsin • Bile • Intestinal juices • Maltase, lactase, sucrase • Peptidase • Steapsin

14. Absorption in the Small Intestine • Villi • Makes absorption possible • Each villi contains a network of blood and lymph capillaries • Digested portion passes through the villi into the bloodstream and lacteals • Undigested portion passes on to the large intestine

15. Accessory Organs of Digestion • Pancreas • Functions both as an exocrine and as an endocrine • Liver • Functions • Manufactures bile • Produce and store glucose in the form of glycogen • Detoxify harmful substances • Manufacture blood proteins necessary for blood clotting • Store vitamins A, D and B complex • Converts ammonia into urea • Break down hormones no longer useful • Remove worn-out red blood cells from circulation and recycle the iron content • Gallbladder • Function is to store and concentrate bile when it is not needed by the body

16. Large Intestine • Also called the colon • About 5 feet long • Ileum empties chyme through ileocecal valveinto large intestine • Regions of the large intestine • Cecum and appendix • Ascending, transverse, and descending colon • Sigmoid colon • Anal canal • Functions • Absorption of fluid and electrolytes and the elimination of waste products

17. General Overview of Digestion • Mouth • Bolus • Pharynx • Swallowing • Esophagus • Peristalsis • Stomach • The action of gastric juices is helped by the chuming of the stomach walls • Semiliquid food is called chyme • Small intestine • Process of digestion is completed and absorption occurs • Digestion of protein, fats and carbohydrates • Absorption of nutrients

18. Action in the Large Intestine • Absorption • Bacterial action • Gas formation • Fecal formation • Defecation

19. Metabolism • Within the cells, nutrients are changed into energy • Aerobic metabolism • Anaerobic metabolism