Ingestion of food GIT GIT Secretions Dr.Rashid Mahmood
Activation of Pepsinogen Proteins in food Nervous system Gastrin HCl Causes proteolysis Pepsinogen Pepsin Contd…..
Pepsinogen activation in stomach lumen
Types of Pepsinogen Pepsinogen I Pepsinogen II
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
Nervous system HCl Causes proteolysis Pepsinogen Pepsin
Pepsinogen activation in stomach lumen
Types of Pepsinogen Pepsinogen I Pepsinogen II
Intrinsic factor Parietal cells Absorption of B-12 in ileum Chronic gastritis→ Achlorhydria→ Pernicious Anemia
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
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
Stimulation of Gastric Acid Secretion
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
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
Phases of Gastric Secretion 1 20% 1 Cerebral cortex & Appetite center of lower brain 2 Sight Smell Thought Taste 70% 3 10%
Intestinal phase of Gastric Secretion All these factors also ↓the gastric motility Hormones: Secretin CCK GIP VIP Somatostatin Initially slight stimulation
Gastric secretion during inter digestive period Small amount Mainly mucus Little pepsin No acid ↑ by emotional stress → Peptic ulcer
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…..
Secretion of Bicarbonate by Pancreas 5 4 2 3 1 6
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
Rate of Pancreatic secretion
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
Effects of Pancreatic failure Effect on Pancreas Effect on digestion Effects on absorption
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
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
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