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Chapter 15

Chapter 15. The Digestive System Day 1. Introduction. 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:

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Chapter 15

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  1. Chapter 15 The Digestive System Day 1

  2. Introduction • 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

  3. 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

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

  5. 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

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

  7. 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

  8. 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

  9. 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

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

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

  12. 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

  13. 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

  14. Teeth • Two Sets • Primary Teeth-deciduous • 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

  15. 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

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

  17. 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

  18. 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

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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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.

  25. 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?

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