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THE DIGESTIVE SYSTEM II

THE DIGESTIVE SYSTEM II. D. C. Mikulecky Professor of Physiology Virginia Commonwealth University. PANCREATIC SECRETIONS. THE PANCREAS IS BOTH ENDOCRINE AND EXOCRINE THE EXOCRINE PANCREAS SECRETES DIGESTIVE ENZYMES AND AN AQUEOUS ALKALINE FLUID PANCREATIC SECRETION IS HORMONALLY REGULATED

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THE DIGESTIVE SYSTEM II

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

  2. PANCREATIC SECRETIONS • THE PANCREAS IS BOTH ENDOCRINE AND EXOCRINE • THE EXOCRINE PANCREAS SECRETES DIGESTIVE ENZYMES AND AN AQUEOUS ALKALINE FLUID • PANCREATIC SECRETION IS HORMONALLY REGULATED • PANCREATIC SECRETIONS REACH THE SMALL INTESTINE VIA THE COMMON BILE DUCT

  3. THE ENDOCRINE PANCREAS • INSULIN AND GLUCAGON • IMPORTANT IN THE CONTROL OF GLUCOSE, FAT AND PROTEIN METABOLISM • ACT IN OPPOSITE WAYS

  4. A FUNCTIONAL UNIT OF THE EXOCRINE PANCREAS DUCT ACINUS

  5. AQUEOUS COMPONENT OF PANCREATIC SECRETION • COMPOSITION CHANGES WITH SECRETION RATE (TRANSIT TIME) • DUCTILE CELLS SECRETE BICARBONATE AND WATER • CHLORIDE AND BICARBONATE VARY RECIPROCALLY • SODIUM AND POTASSIUM ARE LIKE IN PLASMA

  6. HORMONAL CONTROL OF PANCREATIC SECRETION • ACID IN DUODENAL LUMEN >SECRETIN: STIMULATES PANCREATIC DUCT CELLS TO PRODUCE SIGNIFICANT QUANTITES OF AQUEOUS ALKALINE SECRETION • FAT AND PROTEIN IN DUODENAL LUMEN>CHOLECYSTOKININ (CCK):STIMULATES PANCREATIC ACINAR CELLS TO SECRETE DIGESTIVE ENZYMES

  7. HORMONES SECRETED IN DUODENUM SIGNAL THE COMPOSITION OF THE INCOMING CHYME • SECRETIN • CHOLECYSTOKININ

  8. 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

  9. 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

  10. FUNCTIONS OF THE LIVER • METABILIC PROCESSING OF ABSORBED FOOD • DETOXIFICATION2 • SYNTHESIS OF PLASMA PROTEINS • STORAGE OF GLYCOGEN AND FAT, ETC. • REMOVAL OF BACTERIA AND WORN-OUT RBC • EXCRETION OF CHOLESTEROL AND BILIRUBIN

  11. BILE SECRETION, STORAGE, AND CIRCULATION • SECRETED BY THE LIVER • RECYCLED THROUGH ENTEROHEPATIC CIRCULATION • STORED IN GALL BLADDER

  12. LIVER BLOOD FLOW INFERIOR VENA CAVA AORTA HEART HEPATIC VEIN HEPATIC ARTERY LIVER HEPATIC PORTAL VEIN ARTERIES TO DIGESTIVE TRACT STOMACH AND SMALL INTESTINE

  13. BILE SALT CIRCULATION LIVER GALL BLADDER SPHINCTER OF ODDI DUODENUM

  14. S.I. MOTILITY • SEGMENTATION CONTRACTIONS • PACEMAKER CELLS • MIXING AND PROPULSION

  15. SEGMENTATION CONTRACTIONS • INITIATED BY PACEMAKER CELLS • MIXING ACTION • MOVES CHYME DOWNWARD • ILEOCECAL VALVE

  16. S.I. SECRETIONS • MANLY MUCOUS • NO DIGESTIVE ENZYMES

  17. DIGESTION • MAINLY IN THE SMALL INTESTINE • PANCREATIC ENZYMES • BRUSH BORDER ENZYMES

  18. MAINLY IN THE SMALL INTESTINE • SALIVARY AMYLASE • ACID AND PEPSIN IN THE STOMACH • ENZYMES COME FROM PANCREAS

  19. PANCREATIC ENZYMES • PROTEOLYTIC: BREAK PROTEINS DOWN TO SMALLER PEPTIDE FRAGMENTS AND/OR AMINO ACIDS • PANCREATIC AMYLASE BREAKS STARCH DOWN TO OLIGOSACHHARIDES AND DISACCHARIDES • PANCREATIC LIPASE, PHOSPHOLIPASE AND OTHERS • OTHERS

  20. ENZYME PRECURSORS ARE A WAY OF PROTECTING THE GUT FROM SELF-DIGESTION • PEPSIN IN THE SOMACH AND PROTEOLYTIC ENZYMES IN THEM PANCREAS • SECRETED IN AN INACTIVE FORM, LONGER MOLECULE • REMOVAL OF A SEGMENT ACTIVATES THEM

  21. BRUSH BORDER ENZYMES • CARBOHYDRATES: DISACCARIDASES IN BRUSH BORDER MEMBRANE FINISH THE JOB • PROTEINS: ALSO POLY AND DI-PEPTIDASES • TRANSPORT SYSTEMS ARE NEAR-LESSENS THE OSMOTIC EFFECT?

  22. ABSORPTION: THE SMALL INTESTINE IS THE ABSORBING ORGAN • LARGE SURFACE AREA • ACTIVE SODIUM TRANSPORT • FLUID AND ELECTROLYTES • SUGARS AND AA BY SECONDARY ACTIVE TRANSPORT • FAT • VITAMINS AND MINERALS

  23. FLUID AND ELECTROLYTE ABSORPTION IS BY A SPECIAL PROCESS: ISOTONIC TRANSPORT • THE WHOLE TISSUE (SODIUM TRANSPORTING EPITHELIUM) IS INVOLVED • SODIUM/POTASSIUM ATPASE PUMPS ONLY ON BASOLATERAL CELL MEMBRANES • TIGHT JUNCTIONS VS LOOSE SEROSAL SIDE (6-PACK ANALOGY)

  24. An Epithelial Membrane in Cartoon Form:

  25. A Network Model of Coupled Salt and Volume Flow Through an Epithelium CL PL LUMEN AM TJ BL CELL BM BLOOD PB CB

  26. Sodium Reabsorption PUMP: Na/K ATPase Plasma Sodium Lumen Cells Potassium Chloride Water

  27. Sodium Reabsorption PUMP: Na/K ATPase Plasma Sodium Lumen Cells Potassium Chloride Water

  28. Potassium Secretion PUMP: Na/K ATPase Plasma Sodium Lumen Cells Potassium Chloride Water

  29. THE CURRAN-MACINTOSH MODEL HYPERTONIC FLUID INJECTED FLUID MOVES R ---> L B A C MEMBRANES: TIGHT LOOSE

  30. SOURCES OF WATER AND ELECTROLYTES IN GUT(ML/DAY), EXCLUDING INTESTINAL SECRETIONS • IMBIBED: 2,000 • SECRETIONS: • SALIVA 1,500 • GASTRIC JUICE 2,000 • PANCREATIC JUICE 1,500 • BILE 500 • INTESTINAL 1,500 • -----------------------------------------------------------TOTAL: SECRETED + IMBIBED 9,000

  31. SITES OF ABSORPTION SMALL INTESTINE 8,500 COLON 400 --------------------------------------------------------------TOTAL ABSORBED 8,900 (IN FECES 100)

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