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Ingestion of food GIT GIT Secretions Dr.Rashid Mahmood
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Activation of Pepsinogen
Proteins in food Nervous system Gastrin HCl Causes proteolysis Pepsinogen Pepsin Contd…..
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Pepsinogen activation in stomach lumen
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Types of Pepsinogen Pepsinogen I Pepsinogen II
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3. Pyloric glands Structurally similar to oxyntic glands but
Few peptic cells Almost no parietal cells Mostly mucous cells Small amount of Pepsinogen Mucus Lubrication Protection Gastrin Secreted by G cells located in pyloric glands
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Nervous system HCl Causes proteolysis Pepsinogen Pepsin
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Pepsinogen activation in stomach lumen
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Types of Pepsinogen Pepsinogen I Pepsinogen II
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Intrinsic factor Parietal cells Absorption of B-12 in ileum
Chronic gastritis→ Achlorhydria→ Pernicious Anemia
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3. Pyloric glands Structurally similar to oxyntic glands but
Few peptic cells Almost no parietal cells Mostly mucous cells Small amount of Pepsinogen Mucus Lubrication Protection Gastrin Secreted by G cells located in pyloric glands
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Stimulation of Gastric Acid Secretion
Food in stomach (Proteins) Nervous signals Gastrin cells Endocrine signals ECL (Enterochromafin-like cells) in oxyntic glands in body of stomach Gastrin Stimulation of Gastric Acid Secretion H2 Receptors (in Parietal cells) Histamine
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Stimulation of Gastric Acid Secretion
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Gastrin Secreted by G cells located in pyloric glands Polypeptide
2 forms (both important) G-34 G-17 (More abundant) Stimulated by proteins Secreted into stomach Carried to ECL cells in body of stomach by MIXING movements of the stomach
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Phases of gastric secretion
Three phases Cephalic phase Before food enters stomach Sight, smell, thought Taste, food being eaten Gastric phase When food in in stomach Intestinal phase When food reaches upper portion of small intestine
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Phases of Gastric Secretion
1 20% 1 Cerebral cortex & Appetite center of lower brain 2 Sight Smell Thought Taste 70% 3 10%
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Intestinal phase of Gastric Secretion
All these factors also ↓the gastric motility Hormones: Secretin CCK GIP VIP Somatostatin Initially slight stimulation
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Gastric secretion during inter digestive period
Small amount Mainly mucus Little pepsin No acid ↑ by emotional stress → Peptic ulcer
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For digestion of Proteins (Trypsin, Chymotrypsin, Elastase, Carboxypeptidase)
Inactive (Proenzymes) Trypsinogen, chymotrypsinogen, procarboxypolypeptidase Trypsin, Chymotrypsin, Elastase → Endopeptidases Carboxypolypeptidase → Exopeptidases Mechanism of stimulation of proenzymes Chyme Enterokinase Intestinal mucosa Activation of Proenzymes inside lumen of intestine Contd…..
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Secretion of Bicarbonate by Pancreas
5 4 2 3 1 6
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Functions of HCO3-- Neutralize acid pH of stomach
Optimum pH for pancreatic enzymes Blockage of digestive action of digestive enzymes (because digestive enzymes of stomach become inactivated at pH>3-4.5
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Rate of Pancreatic secretion
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Diseases of pancreas Pancreatic failure
Causes Pancreatitis Acute Chronic Causes of Pancreatitis: Alcohol Blockage of Ampulla of Vater by Gall Stone Blockage of Pancreatic duct by at Ampulla of Vater by Gall Stone Removal of head of Pancreas due to malignancy
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Effects of Pancreatic failure
Effect on Pancreas Effect on digestion Effects on absorption
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Effects of Pancreatic failure
Effect on Pancreas Blockage → accumulation of Pancreatic enzymes → overcoming the Trypsin Inhibitor → activation of Trypsinogen → formation of Trypsin and other Proteolytic enzymes →digestion of Pancreas itself Effect on digestion Loss of digestive enzymes Copious fatty feces ½ to 1/3 effect on carbohydrate & protein digestion Undernutrition
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3. Effects of Pancreatic failure on absorption
More effect on Fats absorption Steatorrhea Acid inhibits lipase ↓ alkaline secretion by pancreas → ↓ pH Impaired absorption of Carbohydrates Proteins Calcium Vitamin K
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Summary Slide Pancreatic Secretion
Components of Pancreatic secretion Pancreatic Digestive Enzymes For digestion of Proteins, Carbohydrates and Fats Bicarbonate and water Functions of HCO3-- Regulation/ control of Pancreatic Secretion (Factors affecting) Phases of Pancreatic secretion Diseases of pancreas Pancreatic failure
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