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Human Systems

Human Systems. 8.3 Ingestion. Ingestion. There are four components of the digestive process: Ingestion – the taking in of nutrients Digestion – the breakdown of complex organic molecules into smaller components Absorption – the transport of digested nutrients to the cells of the body

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Human Systems

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  1. Human Systems 8.3 Ingestion

  2. Ingestion There are four components of the digestive process: • Ingestion – the taking in of nutrients • Digestion – the breakdown of complex organic molecules into smaller components • Absorption – the transport of digested nutrients to the cells of the body • Egestion – the removal of food waste from the body

  3. Salivary Glands and Teeth • Saliva: contains amylase- break down starches (complex carbs into simple carbs)- lubricates food • Flavour: cells of tastebuds- food particles dissolved in saliva penetrate cells • Teeth: physical digestion- Incisiors – cutting- Canines – tearing- Premolars – crushing- Molars (wisdom) • Covered in enamel – strongest substance in body

  4. Esophagus • Food in mouth: forms bolus when mixed with saliva • Travels from mouth to stomach via esophagus • Bolus stretches smooth muscle walls – activates peristalsis • Peristalsis – rhythmic contractions of smooth muscle- move food along GI tract (even against gravity)- only time voluntary: swallowing and egestion • Epiglottis: flap of tissue that prevents food from entering trachea

  5. Stomach • Site of food storage • Initial protein digestion • 3 layers of muscle: contractions churn food • Sphincters: top and bottom- Lower esophageal sphincter (LES) – top - Pyloric sphincter – bottom • Stores ~ 1.5 L of food (ridges expand) • Contraction mixes food with gastric juice from parietal cells • Gastric juice composed of:- mucous- hydrochloric acid- pepsinogens- other substances • Hormone gastrin triggers release

  6. Stomach • Cells in stomach release gastric juice (~500 mL, large meal) • Mucous lining: alkaline and protects stomach lining • HCl – kills harmful substances ingested with food- pH in stomach roughly 2.0 • Presence of HCl converts pepsinogen to PEPSIN (active form)- breaks proteins into polypeptides- pepsinogen diffuses through cell membrane and mucous lining and when in contact with HCl, converts to PEPSIN • Pepsin breaks down food protein, not stomach proteins Rugae and Pepsin

  7. Peptic Ulcers • Mucous layer breaks down • Stomach lining exposed to HCl and pepsin • Begins to break down cell membranes- increase in blood flow and acid secretions- more tissue burned • “hole” in stomach lining • Most result of bacterium Helicobacter pylori

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