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17.1: Introduction • Digestion is the mechanical and chemical breakdown of foods into forms that cell membranes can absorb • Organs of the digestive system carry out these processes, as well as ingestion, propulsion, absorption and defecation • The digestive system consists of the alimentary canal extending from the mouth to the anus, plus accessory organs that empty into the alimentary canal 1 17.2: General Characteristics of the Alimentary Canal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • The alimentary canal is a muscular tube about 8 meters long Tongue .5 meter (from tongue to duodenum) Esophagus Duodenum 5.5 – 6.0 meters (small intestine) Gallbladder Stomach 1.0m Pancreas Jejunum (2.2 – 2.4 m) Ileum (3.3 – 3.6 m) Appendix 1.5 meters (large intestine) Cecum Large intestine 2 Anus 3 Innervation of the Tube • Branches of the sympathetic and parasympathetic divisions of the autonomic nervous system extensively innervate the alimentary canal, including: • Submucosal plexus – controls secretions • My enteric plexus – controls gastrointestinal motility • Remember: • Parasympathetic impulses – increase activities of digestive system • Sympathetic impulses – inhibit certain digestive actions 4