Digestive System

Digestion The breaking down of food molecules for use by body cells Types: Mechanical— physically breaking down large food particles into smaller food particles Chemical— chemical reactions that break down into usable molecules

Digestive Functions Ingestion: taking food into the body Movement: transportation of food throughout the body Deglutition: swallowing Peristalsis: moves material through digestive tract; wave like contractions of smooth muscle Absorption: bringing usable molecules into the bloodstream Mixing: combining substances together to form one mass Churning: to make a substance through agitation Secretion: lubricate, liquefy, digest Defecation: elimination of unused substances

Names of Digestive System Continuous tube from the mouth to anus Approximately 30 feet long Known as: Digestive system Gastrointestinal (GI) tract Alimentary canal

Four Layers of Tissues Mucosa: innermost, mucous membrane Submucosa: vascular, holds mucosa in place Muscularis: smooth muscle to move food Serosa: outermost layer continuous with the mesentery

Mouth Oral cavity: opening surrounded by hard & soft palate, teeth, cheeks, tongue Lips: lined with mucous membrane and covered with skin Labial frenulum— attaches lips to gums Uvula— prevents food from entering the nasal cavity when swallowing

Mouth Tongue— skeletal muscle covered with mucous membrane Shapes chewed food with saliva into a ball— bolus Lingual frenulum— limits tongue movement Papillae— cover surface and sides of tongue

Salivary Glands Parotid: under skin in front of ears Submandibular: under base of tongue and below mandible Sublingual: under anterior portion of the tongue Saliva: 99.5% water, 0.5% other stuff Salts—to buffer chemicals Mucin—with forms mucous with matter Lysozyme—kill bacteria Amylase—starch digesting enzyme

Teeth

Teeth Dentin-is a tissue that is calcified and consists of tiny tubules or tubes. It is the second layer of the tooth and is normally covered by enamel and covers the pulp, making up the majority of the tooth's structure. Enamel - the first layer of tooth that is visible in the mouth, is a porous, calcified substance made from crystalline calcium phosphate. Enamel appears to be a soft beige to white color, yet it is semi-translucent allowing the color of the dentin layer to penetrate through. Enamel is also the hardest substance in the body. Pulp- the most vital part of the tooth, the pulp originates in the center of the tooth, underneath the enamel layer and dentin layer, in the pulp chamber. The pulp contains blood vessels, connective tissue, and large nerves. The pulp, also commonly referred to as the nerve, branches out and continues down each root through the canals of the tooth and stops just shy of the apex, or tip of the tooth. Crown- visible portion of tooth Root- portion of tooth underneath the gum Periodontal membrane (aka periodontal ligament)- connective tissue deep to the cementum that connects to bones or cartilages, serving to support and strengthen the joint between the tooth and the gum Cementum- a layer of tough, yellowish, bone-like tissue that covers the root of a tooth. It helps hold the tooth in the socket

Teeth Ability to chew food—mastication 2 sets of teeth in lifetime Deciduous teeth-baby teeth Permanent teeth-32 adult teeth Types of teeth Incisors Canines Premolars Molars

Digestion in Mouth Mechanical: mastication Chemical: salivary amylase AKA chewing Chemical: salivary amylase Breaks down starch

Pharynx Common pathway for food and air Skeletal muscle lined by mucous membrane

Esophagus Muscular tube that lies closed behind the trachea Transports food to stomach Secretes mucous to lubricate and aid transport

Deglutition (swallowing) Voluntary stage: tongue pushes bolus into pharynx Pharyngeal stage: involuntary; soft palate & uvula close off nasal passage, epiglottis seals the larynx; breathing is interrupted Esophageal stage: food is pushed down by waves of muscular movements called PERISTALSIS