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Anatomy and Functions
This Sqadia video demonstrates about Gastric Secretion. Anatomically stomach has 2 major parts body and Antrum. And Physiologically it also has two parts Orad Portion and Caudad portion. The stomach is a J-shaped dilated portion of the alimentary tract situated in the epigastric, umbilical and left hypochondriac regions of the abdominal cavity. The stomach is continuous with the oesophagus at the cardiac sphincter and with the duodenum at the pylocric sphincter. It has two curvatures, the lesser curvature is short, lies on the posterior surface of the stomach and is the downwards continuation of the posterior wall of the oesophagus. Just before the pyloric sphincter it curves upwards to complete the J shape. Where the oesophagus joins the stomach, the anterior region angles acutely upwards, curves downwards forming the greater curvature the slightly upwards towards the pyloric sphincter. Motor functions of stomach involves 1. Storage function and 2. Digestive function. Gastric juice is Mixture of secretions from all glands of stomach. It is Thin, acidic and colorless. Its essential constituents are Hcl, mucous, rennin and pepsin.
Gastric glands involve Single cell mucous glands (Located in whole stomach cabinet), Oxyntic glands (Located in body and fundus) and Pyloric glands (Located in antrum of stomach). Functions of mucous are Thick secretion of water, electrolytes, mixture of glycoproteins, Adheres to food and spreads as a thin film over the surface, Coats gut wall, prevents actual contact of food particles with mucosa. Lubricates passage of food particles through GIT, Adheres fecal particles, forms fecal masses, Resistant to digestion by GIT enzymes. Mucous gylcoproteins buffer acids or alkalis. It Contains HCO3 - ions which neutralize acids.
Secretion of HCL, Pepsinogen and Intrinsic Factor
In Mechanism of HCL secretion Chloride actively transported from cytoplasm of parietal cell into canaliculi. -40 to -70 mV in canaliculi. K+ passively passes to canaliculi. H2O dissociates into hydroxyl ions in cell cytoplasm. H+ actively secreted into canaliculi in exchange for K+, catalyzed by ATPase, passes by osmosis into canaliculi to dilute HCL. CO2 in in oxyntic cell cytoplasm combines with H2O to form H2CO3 which dissociates into H+ and HCO3 -. H+ combines with OH- of step 2 to form H2O. HCO- 3 diffuses out into blood in exchange for Cl-. Pepsin functions as an active proteolytic enzyme in a highly acid medium (1.8 to 3.5). Intrinsic factor is secreted by parietal cells along with Hcl. IF is essential for absorption of vit B12 in the ileum. If acid producing parietal cells destroyed (chronic gastritis), person develops anchlorhydria and pernicious anemia.
Stimulation, Inhibition and Phases of Gastric Secretion
Vagal stimulation has Direct pathway in which Vagus N innervates parietal cells, stimulates H+ secretion. Neurotransmitter is Ach, receptor is muscarinic M3, and second messengers for cck are IP3 and Ca2+. Vagal Stimulation has Indirect pathway in which vagus N innervates G cells and stimulates gastrin secretion which stimulates H+ secretion by endocrine action. Neurotransmitter is GRP. Atropine, cholinergic muscarinic antagonist inhibits H secretion by blocking the direct pathway, which uses Ach. Gastrin is released in response to eating a meal. It stimulates H+ secretion by interacting with CCKb receptor on parietal cells. Second messenger for gastrin on parietal cell is IP3/Ca+. Gastrin stimulates ECL cells and histamine secretion, which stimulates H+ secretion. Histamine is released from ECL cells in gastric mucosa and diffuses to nearby parietal cells.
Regulation, Diseases and Analysis of Gastric Secretion
Regulation of Gastric Secretion is stimulated by Gastrin, Acetylcholine and histamine, and it is Inhibited by Somatostatin, Prostaglandin E2 and I2 and Enteric Hormones. Peptic Ulcer Disease (PUD) is break in the lining of the stomach, first part of the small intestine or occasionally the lower esophagus. Zollinger – Ellison Syndrome: Gastrin-secreting tumour or hyperplasia of the islet cells in the pancreas causes overproduction of gastric acid, resulting in recurrent peptic ulcers. Purpose of Gastric Analysis is to evaluate gastric function by measuring the contents of a fasting patient's stomach the for acidity, appearance, and volume.