Chapter 19-Digestive System

Chapter : Digestive System Overview

Organ Systems 1)Gastointestinal (GI) Tract -Alimentary Canal: continuous tube extending from mouth to anus -Mouth, pharynx, esophagus, stomach, sm. intestines, lg. intestines -About 5-7 meters (16-23ft) long 2) Accessory Organs -Aid in the physical and chemical breakdown of food -Teeth, tongue, salivary glands, liver, gallbladder, pancreas

Basic Functions 1)Ingestion: taking in food 2)Secretion: release ≈ 7 liters of water, acid, buffers, enzymes 3)Mixing and Propulsion: contraction/relaxation of smooth muscle pushes food/secretion mixture down GI tract

Basic Functions 4) Digestion: mechanical and chemical 5)Absorption: entrance of fluids, ions, and small molecules into the lining cells of GI Tract 6)Defecation: any non-absorbed material eliminated from body

Four Layers 1)Mucosa - Inner epithelium of GI tract 2)Submucosa -Connective tissue -Contains blood and nerve supply 3)Muscularis -Thick layer of muscle 4)Serosa -Outer layer -Simple squamous epithelium SUBMUCOSA MUSCULARIS SEROSA MUCOSA

Chapter Mouth

Oral Cavity -Formed by the cheeks, hard and soft palates, and tongue -Hard palate: roof of the mouth -Soft palate: back of the mouth, including the uvula -Tongue: accessory organ composed of skeletal muscle covered by a mucous membrane -Lingual frenulum: a folded membrane in the midline of the undersurface that limits movement -Papillae: small projections on the upper surface and sides Lingual frenulum Hard palate Soft palate Uvula

Salivary Glands -Three pairs (accessory organs) that lie outside oral cavity -Release saliva into ducts emptying into oral cavity 1)Parotid glands 2)Submandibular glands 3)Sublingual glands -Saliva = 99.5% water and 0.5% solutes -Lubricates food -Salivary amylase begins digestion of starches in mouth

Anatomy of Teeth -Accessory organs located in bony sockets of mandible and maxillae -Three major external regions: 1)Crown 2)Neck 3)Root -Majority of tooth made up of dentin -Calcified connective tissue -Crown covered in enamel -Root covered in cementum CROWN NECK ROOT Enamel Dentin Cementum

Anatomy of Teeth -Dentin encloses the pulp cavity -Connective tissue containing blood/lymphatic vessels and nerves -Extends into root canals CROWN NECK ROOT Enamel Dentin Cementum Pulp in pulp cavity Root canal

Types of Teeth -Deciduous (20) vs. Permanent (32) -Incisors -Closest to midline -Used for cutting into food -Cuspids (canines) -One pointed cusp used for tearing and shredding -Premolars and molars -Crushing and grinding food Deciduous Permanent

Digestion in the Mouth -Mechanical digestion of food begins in the mouth -Mastication: chewing and mixing of food into bolus -Salivary amylase begins breaking down carbohydrates -Polysaccharides (starch and glycogen) -Disaccharides (maltose) -Monosaccharides (glucose, fructose) Bolus

Chapter 19.4: Pharynx and Esophagus

Esophagus Oropharynx Laryngopharynx Pharynx -A funnel shaped tube composed of skeletal muscle and mucous membrane -Food travels from mouth -> oropharynx -> laryngopharynx -> esophagus

Esophagus -Muscular tube lined with stratified squamous epithelium -Connects the laryngopharynx to the superior part of the stomach -Controls food transport using muscular contraction and sphincters -Upper esophageal sphincter (UES) -Regulates movement of food into esophagus -Lower esophageal sphincter (LES) -Regulates movement of food into stomach

Three Stages of Swallowing 1)Voluntary stage - Movement from mouth to pharynx 2)Pharyngeal stage -Esophageal sphincter relaxes and food moves into esophagus -Breathing interrupted 3)Esophageal stage - Food pushed through esophagus: peristalsis