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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 PANCREATIC SECRETIONS REACH THE SMALL INTESTINE VIA THE COMMON BILE DUCT THE ENDOCRINE PANCREAS INSULIN AND GLUCAGON IMPORTANT IN THE CONTROL OF GLUCOSE, FAT AND PROTEIN METABOLISM ACT IN OPPOSITE WAYS A FUNCTIONAL UNIT OF THE EXOCRINE PANCREAS DUCT ACINUS 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 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 HORMONES SECRETED IN DUODENUM SIGNAL THE COMPOSITION OF THE INCOMING CHYME SECRETIN CHOLECYSTOKININ 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 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 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 STORAGE, AND CIRCULATION SECRETED BY THE LIVER RECYCLED THROUGH ENTEROHEPATIC CIRCULATION STORED IN GALL BLADDER LIVER BLOOD FLOW INFERIOR VENA CAVA AORTA HEART HEPATIC VEIN LIVER HEPATIC PORTAL VEIN HEPATIC ARTERY ARTERIES TO DIGESTIVE TRACT STOMACH AND SMALL INTESTINE BILE SALT CIRCULATION LIVER GALL BLADDER SPHINCTER OF ODDI DUODENUM S.I. MOTILITY SEGMENTATION CONTRACTIONS PACEMAKER CELLS MIXING AND PROPULSION SEGMENTATION CONTRACTIONS INITIATED BY PACEMAKER CELLS MIXING ACTION MOVES CHYME DOWNWARD ILEOCECAL VALVE S.I. SECRETIONS MANLY MUCOUS NO DIGESTIVE ENZYMES DIGESTION MAINLY IN THE SMALL INTESTINE PANCREATIC ENZYMES BRUSH BORDER ENZYMES MAINLY IN THE SMALL INTESTINE SALIVARY AMYLASE ACID AND PEPSIN IN THE STOMACH ENZYMES COME FROM PANCREAS 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 ENZYME PRECURSORS ARE A WAY OF PROTECTING THE GUT FROM SELFDIGESTION PEPSIN IN THE SOMACH AND PROTEOLYTIC ENZYMES IN THEM PANCREAS SECRETED IN AN INACTIVE FORM, LONGER MOLECULE REMOVAL OF A SEGMENT ACTIVATES THEM BRUSH BORDER ENZYMES CARBOHYDRATES: DISACCARIDASES IN BRUSH BORDER MEMBRANE FINISH THE JOB PROTEINS: ALSO POLY AND DIPEPTIDASES TRANSPORT SYSTEMS ARE NEARLESSENS THE OSMOTIC EFFECT? 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 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) An Epithelial Membrane in Cartoon Form: A Network Model of Coupled Salt and Volume Flow Through an Epithelium LUMEN AM CL PL TJ BL CELL BM BLOOD CB PB Sodium Reabsorption PUMP: Na/K ATPase Sodium Lumen Cells Potassium Plasma Chloride Water Sodium Reabsorption PUMP: Na/K ATPase Sodium Lumen Cells Potassium Plasma Chloride Water Potassium Secretion PUMP: Na/K ATPase Sodium Lumen Cells Potassium Plasma Chloride Water THE CURRAN-MACINTOSH MODEL HYPERTONIC FLUID INJECTED FLUID MOVES R ---> L A B MEMBRANES: TIGHT C LOOSE 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 SITES OF ABSORPTION SMALL INTESTINE 8,500 COLON 400 -------------------------------------------------------------TOTAL ABSORBED 8,900 (IN FECES 100)
