The Digestive System Day 1 Chapter 15 The Digestive System Day 1

Introduction Covers 186 square meters Digestive System: Made up of the alimentary canal which extends from the mouth to anus Includes: Mouth, pharynx, esophagus, stomach, small intestine, large intestine, recturm, and anus Accessory Organs: Salivary glands, liver, gallbladder and pancreas Covers 186 square meters

Intro Cont. Digestion: The chemical and mechanical breakdown of foods and the absorption of the resulting nutrients by cells. Mechanical Digestion Breaks large pieces into smaller ones without altering the chemical composition Chemical Digestion: Breaks food into simpler chemicals

General Characteristics Alimentary Canal Muscular tube, roughly 8 meters in length Structure of the Wall 4 layers Mucosa Membrane Submucosa Muscular Layer Serosa

Mucosa Membrane Made up of epithelium, connective tissue and small amounts of smooth muscle Contains folds or tiny projections that extend into the passageway called LUMEN Increase absorptive surface are Secrete mucus and digestive enzymes Protects tissues beneath it and carries on secretion and absorption

Submucosa Layer Made up of loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves Nourishes surrounding tissues and carries away absorbed materials

Muscular Layer Produces movements of the tube Contains two types of smooth muscle Circular Fibers Contraction causes decrease in tube’s diameter Longitudinal Fibers Contraction leads to shortening of tube

Serosa Layer Outer covering Also called visceral peritoneum Protect underlying tissues and secrete serous fluid which moistens and lubricates tube’s outer surface Allows other organs in abdominal cavity to slide freely against one another

Movements of the Tube Two types of motor movements Mixing Movements Caused by smooth muscle contracts rhythmically Segmentation: alternately contracting and relaxing the smooth muscle in nonadjacent segments Occurs in stomach Propelling movements Peristalsis: wavelike motion that pushes contents of tube ahead Occurs in esophagus and intestines

Mouth Receives food and begins digestion by mechanically breaking up solid particles and mixing them with saliva Mastication

Cheeks and Lips Cheeks Lips Form lateral walls of mouth Contain sensory receptors that judge temp. and texture of food

Tongue Fills oral cavity Responsible for mixing food with saliva and moving food towards pharynx during swallowing Papillae Rough projections on tongue that provide friction to help handle food Lingual Frenulum Connects tongue to floor of mouth Lingual Tonsils: Posterior portion Lymphatic tissue

Palate Forms roof of oral cavity Anterior portion-hard palate Muscular posterior portion-soft palate Uvula Cone-shaped projection in back of mouth Palatine Tonsils and Pharyngeal Tonsils-adenoids Masses of lymphatic tissues that protect the body against infection Commonly removed

Teeth Two Sets Primary Teeth-deciduous Secondary Teeth 20 Erupt though gums in regular intervals from 6 months-2-4 years of age Usually shed in the same order they erupted Secondary Teeth Push primary teeth out of sockets 32 Erupt 6 years-17-25 years with wisdom teeth

Teeth Cont. Role in digestion Begin mechanical digestion by breaking food into smaller pieces Increases surface area of food to allow for digestive enzymes to work more effectively Parts to a tooth Crown-projects beyond gum Root-below gums Neck-portion where crown and root meet Enamel-glossy white, covers crown, consists of calcium salts, hardest substance in body, never replaced when damaged Dentin-bulk of tooth beneath enamel Pulp-contains blood vessels, nerves, and connective tissue Root Canals -area where blood vessels and nerves reach pulp Cementum-bonelike material that helps attach tooth to jaw Periodontal Ligament -contains blood vessels and helps attached tooth to jaw

Salivary Glands Secrete saliva that helps moisten and bind food particles Begins chemical digestion by enzyme amylase Helps cleanse the mouth and teeth

Salivary Secretions Each gland has two types of secretory cells Serous Produce a watery fluid that includes digestive enzyme salivary amylase Enzyme splits carbohydrates Mucous Secretes thick liquid called mucus Binds food particles and lubricates food during swallowing Saliva is produced just by thinking of good foods Saliva stops production in the presence of unpleasant smells or tastes

Major Salivary Glands Three Pairs Parotid Glands largest Lies anterior and somewhat inferior to ears Found between skin, cheeks, and masseter muscle Secretes clear, water fluid that is rich in amylase

Major Salivary Glands Submandibular Gland Located on floor of mouth Secretes both mucous and serous fluid

Major Salivary Glands Sublingual glands Smallest On the floor of mouth inferior to the tongue Secretes primarily mucous type making their secretions thick and stringy

Pharynx-The Crossroads Cavity posterior to mouth which leads to esophagus Do not digest food but functions in swallowing Connects nasal and oral cavities with the larynx and esophagus

Pharynx Cont. Three parts: Nasopharynx-communicates with nasal cavity and provides a passageway for air during breathing, auditory tube connects to nasopharynx Oropharynx-posterior to soft palate and inferior to nasopharynx, allows food and air to pass through Laryngopharynx- inferior to oropharynx, passage way to esophagus

Swallowing Mechanism 3 Stages 1. Food is mixed with saliva, tongue rolls mixture into a mass called bolus, forces bolus into oropharynx 2. Once food reaches oropharynx, swallowing reflex kicks in (See steps on Page 409) 3. Peristalsis transports food into esophagus and on to the stomach

Esophagus Straight, collapsible tube about 25 cm long that allows food to pass from mouth to stomach Mucous glands are scattered throughout Lower Esophageal Sphincter/Cardiac Sphincter Closes the entrance to stomach preventing contents from regurgitating into esophagus. Peristaltic waves allow food to enter stomach.

Review Questions Which organs constitute the digestive system? Describe the wall of the alimentary canal. Name the two basic types of movements in the alimentary canal. How does the tongue function as part of the digestive system? Where are the tonsils located? How do primary teeth differ from secondary teeth? Describe the structure of a tooth. Explain how a tooth is attached to the bone of the jaw. What is the function of saliva? What stimulates salivary glands to secrete saliva? Where are the major salivary glands? Describe the regions of the pharynx. List the major events of swallowing. What is the function of the esophagus?