1. THE DIGESTIVE SYSTEM D. C. Mikulecky Faculty Mentoring Program Virginia Commonwealth University

2. FUNCTIONS OF THE DIGESTIVE SYSTEM zMotility zSecretion zDigestion zAbsorption

3. Motility zThe digestive tract is surrounded by layers of smooth muscle zThese muscles enable mixing and propulsive movement to be carried out by the digestive tract

4. Secretion zDigestion requires that enzymes be secreted by the pancreas and other organs zMucous secretions protect the digestive tract zAcid is secreted in the stomach zThere are other secretions of importance

5. DIGESTION zBreaking down complex foodstuffs into absorbable units by enzymes produced in the digestive system zInvolves the breakdown of carbohydrates, proteins fats, and other foods

6. Absorption zAll other functions support this one zThis is how we obtain the necessary fuel for our cells

7. THE DIGESTIVE TRACT zMouth and pharynx zEsophagus zStomach zSmall Intestine zLarge Intestine zAnus

8. THE DIGESTIVE TRACT Lumen Mucosa Submucosal Plexus Circular Muscle Myenteric Plexus Logitudinal Muscle Extrinsic Nerves

9. ACCESSORY DIGESTIVE ORGANS zSalivary Glands zExocrine Pancreas zBilliary System: (Liver and Gallbladder)

10. CONTROL OF DIGESTIVE SYSTEM External Influences Local Influences Receptors in Digestive Tract Intrinsic Nerve Plexuses Extrinsic Autonomic Nerves GI Hormones Smooth muscle Exocrine Gland Cells Endocrine Gland Cells

11. THE MOUTH zIngestion of food zChewing and swallowing zSalivary secretion

12. Chewing zChewing is the first step in the digestive process zFood is mixed with saliva and broken up into smaller pieces zTaste buds are stimulated

13. Salivary secretion zSalivary amylase: digests carbohydrate zMoistening and lubricating agent zAntibacterial action: lysozyme and rinsing zSolvent for taste stimuli zSpeech facilitation zOral hygene zBicarbonate buffers neutralize acids

14. Swallowing zA programmed all-or-none reflex zChewing and moving the bolus of food back is manly voluntary (striated muscle) zPressure of bolus on pharynx triggers involuntary reflex (smooth muscle) zTongue prevents food from moving back zUvula elevated, sealing nasal passage zLarynx elevates and closure of glottis zRespiration briefly inhibited zPharyngeal muscles force bolus back zPeristaltic waves move bolus through esophagus

15. PERISTALSIS Ringlike contraction sweeps down the esophagus

16. THE STOMACH Esophagus Body Antrum Gastroesophageal Sphincter Pyloric Sphincter Oxyntic Mucosa Pyloric Gland Area Fundus

17. THE STOMACH zMixing and storage organ zHas its own pacemaker: sets frequency of rhythmic peristaltic contractions zPeristalsis becomes stronger in antrum zMotility is highly controlled zNo absorption of food, only aspirin and alcohol

18. FACTORS INFLUENCING GASTRIC MOTILITY zDistension of stomach: increases zFeedback from the small intestine: decreases zControl from CNS zGastrin: increases

19. MIXING MOTIONS IN THE STOMACH Pyloric Sphincter Closed Peristalsis Begins

20. MIXING MOTIONS IN THE STOMACH Pyloric Sphincter Closed Peristaltic Wave Travels Downward

21. STOMACH EMPTYING Pyloric Sphincter Opens Peristaltic Wave Travels Downward Chyme Squirted into Duodenum

22. FACTORS CONTROLLING STOMAC EMPTYING zGastric Motility zEnterogastric reflex: Via intrinsic and autonomic nerves zEnterogastrones: secretin, cholecystokinin (CCK), gastric inhibitory peptide

23. FACTORS IN SMALL INTESTINE CONTROLLING STOMAC EMPTYING zFat zAcid zHypertonicity zDistension

24. GASTRIC SECRETIONS zMucous: Surface Cells z Mucous: Mucous Neck Cells zHydrochloric Acid: Parietal cells zIntrinsic Factor: Parietal Cells zPepsinogen: Chief Cells zGastrin: Only in the Pyloric Gland Area

25. Activation of Pepsin Chief Cell PEPSIN-OGEN HCl Parietal Cell PEPSIN Digests Protein

26. STIMULATION OF GASTRIC SECRETION: Cephalic Phase Seeing, Smelling, Tasting Food Vagus Intrinsic Nerves Pyloric Area Parietal & Chief Cells Gastrin Increased Gastric Secretion

27. STIMULATION OF GASTRIC SECRETION: Gastric Phase Stimuli in Stomach: protein, distension, caffeine, alcohol Vagus Intrinsic Nerves Pyloric Area Parietal & Chief Cells Gastrin Increased Gastric Secretion

28. THE GASTRIC MUCOSAL BARRIER zProtects the cells from contents of stomach zLuminal membranes of cells are impermeable to protons zCells are tightly adjoined zRapid turnover zIf broken, peptic ulcer may result: positive feedback involving histamine

29. Gastrin secretion inhibition zAcid in antrum zremoval of protein as stomach empties