GI 3 Secretory Functions PDF

Gastrointestinal Physiology; Secretory functions of the GI system. Unit 3 Second Semester Second Year Medicine Types of secretory glands Unicellular glands Mucous (goblet) glands Tubular glands Multicellular glands Crypts of Lieberkühn Complex glan...

Gastrointestinal Physiology; Secretory functions of the GI system. Unit 3 Second Semester Second Year Medicine Types of secretory glands Unicellular glands Mucous (goblet) glands Tubular glands Multicellular glands Crypts of Lieberkühn Complex glands Salivary glands Pancreas Liver 2  Stimulation of secretory glands Local stimulation Autonomic innervation Direct contact Parasympathetic Specially for secretion of mucus Stimulates Enteric nervous system Sympathetic Specially submucosal plexus Dual effect Stimuli By reduction of blood supply Tactile stimulation Irritation Distention of the bowel wall Secretion Hormonal stimulation Mucus in the surface Each hormone has its own effect and Digestion products in deep glands source 3  Secretions Organic substances Mucus Endoplasmic reticulum Composition Peptide syntesis Water Golgi complex Electrolytes Peptide process Polysaccharides Vesicles Properties Storage Adherent Release To the wall Calcium mediated Compact contents Exocytosis Coats the mucosa Slippy Resistant Amphoteric 4  Saliva Glands Contents Parotid Serous Serous secretion Ptyalin (amylase) Submandibular Mucus Mix secretion Mucin Sublingual Water Mix secretion Electrolytes Buccal glands Low ClNa Mucus High KHCO3 Other Antibodies Proteolytic enzymes Lysozyme Thiocyanate ions 5  Saliva: production control Daily production: 800-1500 ml. Parasympathetic Sympathetic Stimulus Little stimulation Taste (specially acid) Control centers Receptor at tongue, mouth & pharynx Tactile (smooth) Superior cervical ganglia Receptor at tongue, mouth & pharynx Efferents: Along blood vessel walls From CNS (+ or -) Smell Blood supply Appetite area Parasympathetic vasodilatation Anterior hypothalamus near Salivation itself causes vasodilatation parasympathetic centers Kallikrein breaks bradykinin Stomach & upper small intestine Control centers Superior & inferior salivatory nuclei Afferents: Glosopharingeal & facial nerves Efferents: Vagal nerve 6  Esophageal secretion Mucus Upper two thirds Simple mucous glands Protect from excoriation by food Lower third Compound mucous glands Protect from the gastric acid 7  Gastric secretion Glands Mucous cells Tubular glands Oxyntic or gastric glands Mucous neck cells Oxyntic or parietal cells ClH Intrinsic factor Peptic or chief cells Pepsinogen Pyloric glands Gastrin (G cells) Mucus 8 Acid secretion Enzymes involved H+-K+ ATPase Carbonic anhydrase Na+-K+ ATPase Anion exchanger Gastric fluid composition ClH 150-160 mEq/L ClK 15 mEq/L ClNa Gastric barrier Tight intercellular junctions Mucus 9  Other gastric secretions Pepsinogens (peptic glands) In acid environment it is split to pepsin and activated Inactive at ph>5. The best ph 1.8-3.5 Intrinsic factor (parietal glands) Necessary to absorb vitamin B12 Chronic gastritis causes pernicious anemia Mucus Create a 1 mm. wide alkaline barrier Gastrin (pyloric glands) 10  Control of gastric secretions Stimulation of acid secretion Enterochromaffin-like cells (ECL cells) Release histamine Controlled by gastrin and the enteric nervous system Stimulation of pepsinogen secretion Acetylcholine from vagus or enteric nervous system Response to acid in the stomach Inhibition of gastric secretion Reverse enterogastric reflex Both enteric nervous system and extrinsic sympathetic Hormonal inhibition Secretin, GIP, VIP, somatostatin 11  Phases of gastric secretions Cephalic phase (30% secretion) Neurogenic upper signals that respond to stimuli Conducted by the vagus nerves from the dorsal motor nuclei Gastric phase (60% secretion) Extrinsic long vasovagal reflex to the brain Local enteric reflexes Gastrin mechanism Intestinal phase (10% secretion) Small secretion caused by food in the duodenum Probably mediated by gastrin 12 The bilio-pancreatic complex 13  Pancreatic secretions Enzymes (Accini) Amylase Trypsin inhibitor Proteases Enterokinase Trypsinogen Trypsin Chymotrypsinogen Chymotrypsin Procarboxypeptidase Carboxypeptidase Lipases Pancreatic lipase Cholesterol esterase Phospholipase Bicarbonate & water (Ducts) 14 Bicarbonate secretion 15 Regulation of pancreatic secretions Acetylcholine From parasympathetic and enteric nervous system Stimulates the acini Cholecystokinin I cells at duodenal and proximal jejunal mucosa Proteoses & peptones and long-chain fatty acids Stimulates the acini Secretine S cells at duodenal and proximal jejunal mucosa Starts at ph 4.5-5.0 & raises at ph 3.0 Stimulates the ducts to produce HCO3+ Increases ph to 7.0-8.0 16  Phases of the pancreatic secretion Cephalic & gastric phases Conducted by parasympathetic system Initial & limited production of enzymes at the acini Intestinal Phase Production of secretin and CCK by chyme at the duodenum Copious production of pancreatic juice 17 The bilio-pancreatic complex Bile producers Hepatocites Ductal cells 18  Bile components Liver Gallbladder Water 97.5 g/dl 92 g/dl Biliary salts Bile salts 1.1 g/dl 6 g/dl Bilirubin 0.04 g/dl 0.3 g/dl Emulsify fats Cholesterol 0.1 g/dl 0.3-0.9 g/dl Help absorption Fatty acids 0.1 0.3-1.2 g/dl Lecithin 0.04 g/dl 0.3 g/dl of fats Na+ 145 mEq/L 130 mEq/L K+ 5 mEq/L 12 mEq/L Ca++ 5 mEq/L 23 mEq/L Cl- 100 mEq/L 25 mEq/L HCO3- 28 mEq/L 10 mEq/L 19  Regulation of bile excretion Enterohepatic Cholecystokinin circulation Stimulates the contractions of the gallbladder & opening of Sphincter of Oddi Secretine Stimulates the ducts cells to produce water and sodium bicarbonate Acetylcholine Parasympathetic and enteric nervous system Stimulates the gallbladder contractions 20  Small intestine secretions Brunner’s glands Lieberkühn cripts Alkaline mucus Globet cells Stimuli Mucus Tactile or irritating Enterocites Vagal stimulation Water & electrolytes (1800 ml/d) Secretin Digestive enzymes Sympathetic inhibition peptidases sucrase, maltase, lactase, isomaltase intestinal lipase Regulation Enteric nervous system 21  Colonic secretions Lieberkühn cripts (no villi) Globet cells Mucus Enterocites Water & electrolytes Regulation Parasympathetic Enteric nervous system Tactile stimulation 22