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3.5 The Digestive System

The digestive system consists of several stages that facilitate nutrient processing in the body: ingestion, digestion, absorption, and egestion. In the mouth, mechanical and chemical digestion begins with chewing and saliva, initiating the breakdown of food. The stomach plays a critical role in protein digestion, protected by sphincters and layered structures, while hormones like gastrin regulate digestive juices. Additionally, the mucous layer safeguards the stomach lining, notably from the effects of Helicobacter pylori, which can lead to ulcers. Explore how these processes maintain our health and well-being.

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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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