1. Digestive System

3. 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? 1. Ingestion 2. Peristalsis 3. Digestion 4. Absorption 5. Defecation

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

6. 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

9. 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

10. Where does digestion begin?

11. Mastication Mechanical digestion mixing with saliva

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

14. 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)

17. Swallowing Steps 1. Chew food and mix with saliva into a bolus: voluntary 2. Food reaches the pharynx and stimulates sensory receptors: involuntary reflex 3. Soft palate rises inhibits food from entering… 4. Epiglottis closes over larynx (no breathing) 5. Muscles in lower pharynx relax 6. The constrictor muscles contract and stimulates peristaltic waves 7. Esophagus opens

18. Esophagus

19. 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

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

24. 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

27. 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

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

30. 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

31. 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

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

33. 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

34. 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

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

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

37. 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

38. Digestion Animation http://highered.mcgraw- hill.com/sites/0072495855/student_view0/cha pter26/animation__organs_of_digestion.html http://highered.mcgraw- hill.com/sites/0072495855/student_view0/cha pter26/animation__organs_of_digestion.html http://health.howstuffworks.com/adam- 200142.htm http://health.howstuffworks.com/adam- 200142.htm http://www.constipationadvice.co.uk/constipa tion/constipated-digestive-system.html http://www.constipationadvice.co.uk/constipa tion/constipated-digestive-system.html

39. Gastric Bypass