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Digestive System

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  1. Digestive System

  2. What is Digestion?? • Processes that changes food into simpler forms that can be absorbed thru cell membrane (mechanical means and chemical) What are these processes? • Ingestion • Peristalsis • Digestion • Absorption • Defecation

  3. Alimentary canal Mouth Pharynx Esophagus Stomach Small Large intestines Accessory Organs Salivary glands Liver Gallbladder Pancreas Two Categories of Organs

  4. Alimentary Canal • 9 meters long!! • Large intestines: 1.5 m (~5 feet) • Small intestines: 6 m (~20 feet) • Originates from the endoderm of the embryo

  5. FXN: moves food. HOW? 1. Mixing movements • Smooth muscle contract rhythmically (every 20 sec or so) in the circular muscle layer • Food + digestive juices + mucus 2. peristalsis • Wavelike movements propelling movements • A ring of contractions begin when food expands the tube in the longitudinal layer

  6. Where does digestion begin?

  7. Mastication • Mechanical digestion mixing with saliva

  8. Incisors: 8 Teeth Cuspids (canines): 4 bicuspids (premolars): 8 Molars: 12

  9. Pharynx • Passageway of food into esophagus and air into larynx/trachea • swallowing mechanism (deglutition) • Involuntary Made of muscles called constrictor muscles (pull walls inward during swallowing)

  10. Swallowing Steps • Chew food and mix with saliva into a bolus: voluntary • Food reaches the pharynx and stimulates sensory receptors: involuntary reflex • Soft palate rises inhibits food from entering… • Epiglottis closes over larynx (no breathing) • Muscles in lower pharynx relax • The constrictor muscles contract and stimulates peristaltic waves • Esophagus opens

  11. Esophagus

  12. Esophagus • Straight tube: 25 cm long • Penetrates through an opening: esophageal hiatus (continuous with stomach) • Passageway for food from pharynx to stomach • Contains many mucus glands • Movement of food: • Gravity • Peristaltic waves meet the esophageal sphincter which regulates food into the stomach

  13. Barrette’s esophagus • the abnormal growth of intestinal-type cells from the stomach border, into the esophagus.

  14. How do we know physiology of the Stomach? • 1822: Alexis Martin • Shot himself in the stomach • Left a fistula • Army surgeon studied 8 years • 1984: Barry Marshall from Australia • Hypothesized that bacteria caused gastritis and ulcers • Drank swamp water • Heliobacter pylori IN conclusion: Discoveries are made through observations and experimentation of bizarre phenomenon

  15. Stomach characteristics • J shaped, 25-30 cm long • Under diaphragm on left side • Hold up to 1 liter of contents • Internal Characteristics: • Rugae: mucosal folds • What is the benefit of these folds? • Gastric villi aid in secretion and absorption of gastric juices

  16. Parts of Stomach • Cardiac region • Around esophagus • Fundic • Large ballooned area • Pyloric • Near duodenum • Contains pyloric sphincter muscle

  17. Contents of Gastric Juices • Mucous • Lubricates and protects stomach wall • Prevents pepsin from digesting the protein in stomach wall • Pepsin-most active in acidic environment • Digests proteins into peptides

  18. Contents of Gastric Juices • HCl • Denatures proteins and kills microbes • Intrinsic factors • Aids in absorption of Vit B 12 • Gastrin • Regulatory hormone: regulates contents of stomach to the small intestines

  19. Gastric Cells • Mucus cells: secrete mucus • Chief cells: secrete pepsinogen • Pepsinogen vs. pepsin • Parietal cells: secrete HCl and intrinsic factor • G-cells: secrete gastrin

  20. Regulation of Gastric Secretions • Gastric juice produced continuously • Rate controlled • Neurally- parasympathetic • Acetylcholine- inhibits stomatostatin • Hormonally • Stomatostatin- inhibits acid secretion • Gastrin- increases gastric gland secretion

  21. Phases of Gastric Secretion • Cephalic Phase • Sight, taste, smell, or thought of food • Gastric juice secreted • Gastric Phase • Food enters stomach • Stimulates release of gastrin • Intestinal Phase • Food enters small intestine • Intestinal gastrin released

  22. Gastric Absorption • Stomach • Some water, certain salts, lipid-soluble drugs • Small Intestine • Most nutrients absorbed • Large Intestine • Water, salt

  23. Mixing and Emptying Actions • Chyme • Semifluid paste of food particles and gastric juice • Peristaltic waves- mixes food • Pyloric Sphincter relaxes

  24. Mixing and Emptying Actions • Liquids- rapidly • Solids- remain until well mixed • Fatty foods- 3-6 hours • Proteins- move quickly • Carbohydrates- more rapidly than proteins or fats

  25. Digestion Animation • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html • http://health.howstuffworks.com/adam-200142.htm • http://www.constipationadvice.co.uk/constipation/constipated-digestive-system.html

  26. Gastric Bypass

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