The Digestive System Chapter 23 23.1 – Overview of the Digestive System • Break down food to release and absorb nutrients • Alimentary canal or gastrointestinal (GI) tract is about 25 ft. long from mouth to anus, has 4 layers • Pharynx, esophagus, stomach, small and large intestines • Accessory digestive organs – teeth, tongue, salivary glands, liver, gallbladder, pancreas 23.1 – GI Tract Layers • Mucosa – mucous membrane epithelium in contact with food • Epithelium – non-keratinized, stratified squamous in mouth, esophagus and anal canal. Columnar in stomach and intestines. Interspersed with goblet (secret mucous) and enteroendocrine cells. • Lamina propria – loose connective tissue with blood and lymphatic vessels to transport absorbed nutrients, contain MALT • Muscularis mucosa – smooth muscle always in a state of tension 23.1 - Layers • Submucosa – dense connective tissue between mucosa and muscularis, has blood and lymphatic vessels, and has a collection of nerves called the submucosal plexus • Muscularis – inner circular layer and outer longitudinal layer in the small intestine, mechanical digestion, exposes food to more chemicals, and peristalsis (moving food along the canal). Skeletal muscle at both ends (swallowing and defecation). Stomach adds a third layer of oblique muscle • Serosa – most superficial, only in the region inside the abdominal cavity, loose connective tissue holding the canal in place