Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System The Gastrointestinal (Digestive) System Every cell in the body needs a constant supply of food. The main function of the gastrointestinal system (GI) is to supply nutrients to body cells. Once the body breaks down the food, it must eliminate the waste. The GI system is responsible for the intake of food and its elimination. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Food undergoes three kinds of processing in the body Digestion Mechanical Chemical Absorption Metabolism Catabolism Anabolism 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Digestion Digestion is the process of breaking down food into nutrients that can be absorbed by cells. The gastrointestinal (GI) tract is sometimes referred to as the alimentary canal. It is a tube that extends from the mouth to the anus. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Main Organs of GI System Mouth Pharynx Esophagus Small Intestine Duodenum Jejunum Ileum 6.10 Large Intestine Cecum Colon Ascending Colon Transverse Colon Descending Colon Sigmoid Colon Rectum Anal Canal

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Accessory Organs of GI System Teeth & Tongue Salivary Glands Parotid Submandibular Sublingual Liver Gallbladder 6.10 Pancreas Vermiform Appendix

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Gastrointestinal Tract It has four layers. Serosa - The outer covering It protects the canal and lubricates the outer surface. Muscle - The muscle layer which expands and contracts in motions called peristalsis. It contracts and expands in wavelike motions, called peristalsis, this moves food along the canal. Submucosa - Loose connective tissue containing vessels, glands, and nerves. It nourishes the surrounding tissue and carries waste away from it. Mucosa - A mucous membrane that secrete mucus and digestive enzymes while protecting the tissues within the canal. Converts complex proteins, sugars, and fat molecules so that they can be absorbed and used by the body 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System The Mouth Digestion begins in the mouth with mastication. Teeth – 2 sets – Temporary (20) – Permanent (32) Three sets of salivary glands surrounding the oral cavity secrete saliva. Saliva contains enzymes that break down food and begin the digestion of carbohydrates. Three pairs of glands with ducts: parotid, submandibular, and sublingual glands. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) The Mouth (cont.) 1. Parotid gland. 2. Submandibular gland. 3. Tongue. 4. Tooth. 5. Sublingual gland. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) The Pharynx Passageway for food and air. Epiglottis covers the trachea when we swallow. The Esophagus Contracts rhythmically to move food to stomach. The lower esophageal (cardiac) sphincter (LES), a group of muscles, closes the entrance to the stomach to prevent backflow of food. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) 6.10 The Stomach Pouchlike organ with four regions. Located in the left upper quadrant. The lining of the stomach is relatively thick and has many folds of mucous tissue called rugae Receives food from the esophagus and mixes it with gastric juice to form chyme.

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) Small Intestines (about 20 feet in length) Receive chyme from the stomach. Absorption occurs over 1 to 6 hours. Has 3 parts: Duodenum. Jejunum. Ileum. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) Large Intestines Waste products from digestion stay here for 12 to 24 hours. Main Divisions: Cecum. Colon. – Ascending – Transverse – Descending – Sigmoid Rectum. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) The Liver Not within the GI tract, but performs digestive functions. Changes food nutrients into useable substances. Secretes bile to break down fat. Stores glucose and certain vitamins. Secretes bilirubin. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Organs of the Digestive System (cont.) The Gallbladder Bile from the liver goes into the gallbladder Stores and concentrates bile until it is needed for digestion. It is forced out into the duodenum, where it aids in breaking down fats. The Pancreas Secretes pancreatic juice into the small intestine through its system of ducts. Pancreatic juice contains various enzymes such as amylase and lipase. 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System What is digestion? 6.10

Copyright © The McGraw-Hill Companies, Inc.Chapter 6 Human Structure and Function The Digestive System Digestion is the process of breaking down foods into nutrients that can be absorbed by cells. What is digestion? 6.10