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3.5 The Digestive System

3.5 The Digestive System. Page 183-188. Stages of Digestion. Ingestion-the taking in of nutrients. Digestion- the chemical and mechanical break-down of food into nutrients. Absorption-the taking up of digested molecules into the cells of the digestive tract.

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3.5 The Digestive System

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  1. 3.5 The Digestive System Page 183-188

  2. Stages of Digestion • Ingestion-the taking in of nutrients. • Digestion- the chemical and mechanical break-down of food into nutrients. • Absorption-the taking up of digested molecules into the cells of the digestive tract. • Egestion-the removal of waste food materials from the body.

  3. Mouth • Physical digestion-chewing

  4. Teeth • Incisors-cut food into smaller pieces. • Bicuspids (premolars) and Canines pierce and tear. • Molars crush and grind.

  5. Mouth • Chemical digestion • Saliva -1 Litre per day -makes food wet (mucous, enzymes) -bolus salivary amylase starch  disaccharides

  6. Swallowing • Tongue pushes food back to throat • Soft palate protects nasal openings • Epiglottis protects airways

  7. Peristalsis • Waves of smooth muscle contractions stimulated by the presence of food.

  8. Structure of the Stomach • 2L capacity • Site of protein digestion

  9. Sphincters • Circular muscle • Like the drawstring of a bag • Relaxed, food can move through • Contracted, the opening closes

  10. Stomach Layers: mucosa • innermost layer, mucosa • secretes digestive juices • replaced every 3 days

  11. Stomach layer: submucosa -middle layer -connective tissue with network of nerves and blood

  12. Stomach layers: muscularis • 3 muscle layers that contract and relax

  13. Stomach layer: serosa • Holds stomach in place and lubricates it

  14. chyme • food & gastric juice

  15. Gastrin • Hormone released when food is present in the stomach • 2L of gastric juices released each day • Enzymes digest the protein

  16. Acid hydrochloric acid, pH 2.0-3.0 • Break down of fibrous foods • kills germs • Activates enzymes pepsinogenpepsin • nerves in walls of stomach stimulate churning

  17. Absorption • Water • Medicine (aspirin) • Alcohol

  18. Mucous • Protects the stomach lining from digestion by enzymes and acid

  19. Stomach Ulcers Helicobacter pylori • Neutralizes acid • Burrows into mucous Dr. Robin Warren and Dr. Barry Marshall

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