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THE DIGESTIVE SYSTEM I

Explore the functions and anatomy of the digestive system, from motility to absorption. Learn about key hormones and neural pathways involved in digestion and absorption processes.

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THE DIGESTIVE SYSTEM I

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  1. THE DIGESTIVE SYSTEM I D. C. Mikulecky Professor of Physiology Virginia Commonwealth University

  2. FUNCTIONS OF THE DIGESTIVE SYSTEM • MOTILITY • SECRETION • DIGESTION • ABSORPTION

  3. THE DIGESTIVE TRACT • MOUTH AND PHARYNX • ESOPHAGUS • STOMACH • SMALL INTESTINE • LARGE INTESTINE • ANUS

  4. THE DIGESTIVE TRACT MUCOSA LOGITUDINAL MUSCLE SUBMUCOSAL PLEXUS LUMEN CIRCULAR MUSCLE EXTRINSIC NERVES MYENTERIC PLEXUS

  5. INNERVATION OF THE G.I. TRACT • PARASYMPATHETIC • SYMPATHETIC • INTRINSIC

  6. PARASYMPATHETIC • VAGUS: DOWN TO TRANSVERSE COLON. PREGANGLIONIC CHOLINERGIC NEURONS ORIGNINATE IN MEDULLA • PELVIC: BELOW THAT. PREGANGLIONIC CHOLINERGIC NEURONS ORIGNINATE IN SACRAL S.C.

  7. SYMPATHETIC • GANGLIA OUTSDE G. I. TRACT: CELIAC, SUPERIOR AND INFERIOR MESENTERIC • POSTGANGLIONIC ADRENERGIC FIBERS INNERVATE MYENTERIC AND SUBMUCOSAL PLEXUS

  8. INTRINSIC INNERVATION • SUBMUCOSAL PLEXUS • MYENTERIC PLEXUS • DIFFERENT MEDIATORS: ACh, Nitric Oxide, VIP, Enkephalins, Serotonin, Substance P

  9. G. I. PEPTIDES • HORMONES • NEUROCRINES • PARACRINES

  10. G. I. HORMONES • GASTRIN • CHOLECYSTOKININ (CCK) • SECRETIN • GIP • MOTILIN

  11. GASTRIN • ENDOCRINE CELLS IN PYLORIC STOMACH • STIMULATED BY PROTEIN IN STOMACH • STIMULATES SECRETION BY PARIETAL AND CHIEF CELLS • STIMULATES ILEAL MOTILITY • RELAXES ILEOCECAL SPHINCTER • INDUCES COLONIC MASS MOVEMENTS

  12. SECRETIN • ENDOCRINE CELLS IN DUODENAL MUCOSA • ACID IN DUODENAL LUMEN • INHIBITS GASTRIC EMPTYING • INHIBITS GASTRIC SECRETION • STIMULATES AQUEOUS BICARBONATE SECRETION BY PANCREAS • STIMULATES BICARBONATE RICH BILE SECRETION BYLIVER

  13. CHOLECYSTOKININ • ENDOCRINE CELLS IN DUODENAL MUCOSA • FAT AND PROTEIN IN DUODENAL LUMEN • INHIBITS GASTRIC EMPTYING • INHIBITS GASTRIC SECRETION • CAUSES GALL BLADDER CONTRACTION • CAUSES RELAXATION OF THE SPHINCTER OF ODDI • CONTRIBUTES TO SATIETY

  14. GASRTIC INHIBITORY PEPTIDE (GIP) • STRUCTURALLY RELATED TO SECRETIN AND GLUCAGON • INHIBITS GASTRIC ACIS SECRETION (PHARMACOLOGICAL DOSES) • STIMULATES INSULIN RELEASE

  15. MOTILITY • THE DIGESTIVE TRACT IS SURROUNDED BY LAYERS OF SMOOTH MUSCLE • THESE MUSCLES ENABLE MIXING AND PROPULSIVE MOVEMENT TO BE CARRIED OUT BY THE DIGESTIVE TRACT

  16. SECRETION • DIGESTION REQUIRES THAT ENZYMES BE SECRETED BY THE PANCREAS AND OTHER ORGANS • MUCOUS SECRETIONS PROTECT THE DIGESTIVE TRACT • ACID IS SECRETED IN THE STOMACH • THERE ARE OTHER SECRETIONS OF IMPORTANCE

  17. DIGESTION • BREAKING DOWN COMPLEX FOODSTUFFS INTO ABSORBABLE UNITS BY ENZYMES PRODUCED IN THE DIGESTIVE SYSTEM • INVOLVES THE BREAKDOWN OF CARBOHYDRATES, PROTEINS FATS, AND OTHER FOODS

  18. ABSORPTION • ALL OTHER FUNCTIONS SUPPORT THIS ONE • THIS IS HOW WE OBTAIN THE NECESSARY FUEL FOR OUR CELLS

  19. ACCESSORY DIGESTIVE ORGANS • SALIVARY GLANDS • EXOCRINE PANCREAS • BILLIARY SYSTEM: (LIVER AND GALLBLADDER)

  20. 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

  21. THE MOUTH • INGESTION OF FOOD • CHEWING AND SWALLOWING • SALIVARY SECRETION

  22. CHEWING • CHEWING IS THE FIRST STEP IN THE DIGESTIVE PROCESS • FOOD IS MIXED WITH SALIVA AND BROKEN UP INTO SMALLER PIECES • TASTE BUDS ARE STIMULATED

  23. SALIVARY SECRETION • SALIVARY AMYLASE: DIGESTS CARBOHYDRATE • MOISTENING AND LUBRICATING AGENT • ANTIBACTERIAL ACTION: LYSOZYME AND RINSING • SOLVENT FOR TASTE STIMULI • SPEECH FACILITATION • ORAL HYGENE • BICARBONATE BUFFERS NEUTRALIZE ACIDS

  24. Swallowing • A PROGRAMMED ALL-OR-NONE REFLEX • CHEWING AND MOVING THE BOLUS OF FOOD BACK IS MANLY VOLUNTARY (STRIATED MUSCLE) • PRESSURE OF BOLUS ON PHARYNX TRIGGERS INVOLUNTARY REFLEX (SMOOTH MUSCLE) • TONGUE PREVENTS FOOD FROM MOVING BACK • UVULA ELEVATED, SEALING NASAL PASSAGE • LARYNX ELEVATES AND CLOSURE OF GLOTTIS • RESPIRATION BRIEFLY INHIBITED • PHARYNGEAL MUSCLES FORCE BOLUS BACK • PERISTALTIC WAVES MOVE BOLUS THROUGH ESOPHAGUS

  25. PERISTALSIS RINGLIKE CONTRACTION SWEEPS DOWN THE ESOPHAGUS

  26. THE STOMACH GASTROESOPHAGEAL SPHINCTER ESOPHAGUS FUNDUS BODY OXYNTIC MUCOSA ANTRUM PYLORIC SPHINCTER PYLORIC GLAND AREA

  27. THE STOMACH • MIXING AND STORAGE ORGAN • HAS ITS OWN PACEMAKER: SETS FREQUENCY OF RHYTHMIC PERISTALTIC CONTRACTIONS • PERISTALSIS BECOMES STRONGER IN ANTRUM • MOTILITY IS HIGHLY CONTROLLED • NO ABSORPTION OF FOOD, ONLY ASPIRIN AND ALCOHOL

  28. FACTORS INFLUENCING GASTRIC MOTILITY • DISTENSION OF STOMACH: INCREASES • FEEDBACK FROM THE SMALL INTESTINE: DECREASES • CONTROL FROM CNS • GASTRIN: INCREASES

  29. MIXING MOTIONS IN THE STOMACH PYLORIC SPHINCTER CLOSED PERISTALSIS BEGINS

  30. MIXING MOTIONS IN THE STOMACH PYLORIC SPHINCTER CLOSED PERISTALTIC WAVE TRAVELS DOWNWARD

  31. STOMACH EMPTYING PERISTALTIC WAVE TRAVELS DOWNWARD PYLORIC SPHINCTER OPENS CHYME SQUIRTED INTO DUODENUM

  32. FACTORS CONTROLLING STOMAC EMPTYING • GASTRIC MOTILITY • ENTEROGASTRIC REFLEX: VIA INTRINSIC AND AUTONOMIC NERVES • ENTEROGASTRONES: SECRETIN, CHOLECYSTOKININ (CCK), GASTRIC INHIBITORY PEPTIDE

  33. FACTORS IN SMALL INTESTINE CONTROLLING STOMAC EMPTYING • FAT • ACID • HYPERTONICITY • DISTENSION

  34. GASTRIC SECRETIONS • MUCOUS: SURFACE CELLS • MUCOUS: MUCOUS NECK CELLS • HYDROCHLORIC ACID: PARIETAL CELLS • INTRINSIC FACTOR: PARIETAL CELLS • PEPSINOGEN: CHIEF CELLS • GASTRIN: ONLY IN THE PYLORIC GLAND AREA

  35. ACTIVATION OF PEPSIN CHIEF CELL PEPSIN-OGEN PEPSIN HCL DIGESTS PROTEIN PARIETAL CELL

  36. STIMULATION OF GASTRIC SECRETION: CEPHALIC PHASE SEEING, SMELLING, TASTING FOOD INTRINSIC NERVES PYLORIC AREA VAGUS PARIETAL & CHIEF CELLS INCREASED GASTRIC SECRETION GASTRIN

  37. STIMULATION OF GASTRIC SECRETION: GASTRIC PHASE STIMULI IN STOMACH: PROTEIN, DISTENSION, CAFFEINE, ALCOHOL INTRINSIC NERVES PYLORIC AREA PARIETAL & CHIEF CELLS VAGUS INCREASED GASTRIC SECRETION GASTRIN

  38. THE GASTRIC MUCOSAL BARRIER • PROTECTS THE CELLS FROM CONTENTS OF STOMACH • LUMINAL MEMBRANES OF CELLS ARE IMPERMEABLE TO PROTONS • CELLS ARE TIGHTLY ADJOINED • RAPID TURNOVER • IF BROKEN, PEPTIC ULCER MAY RESULT: POSITIVE FEEDBACK INVOLVING HISTAMINE

  39. GASTRIN SECRETION INHIBITION • ACID IN ANTRUM • REMOVAL OF PROTEIN AS STOMACH EMPTIES

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