GASTRIC SECRETION Dr Shridhar Savadatti.pptx

GASTRIC SECRETION Dr Shridhar Savadatti.pptx

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  GASTRIC SECRETION Dr ShridharSavadatti Professor and HOD DEPARTMENT OF KRIYA SHARERA SCPM Ayurvedic Medical College and Hospital Gonda Uttar Pradesh
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  Structure of Stomachwall  Gastric Glands and its Structure Composition of Gastric Juice Secretion of Gastric Juice  Regulation of Gastric Juice
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  Structure of StomachWall OUTER SEROUS LAYER Formed By Peritoneum MUSCULAR LAYER – Smooth Muscle 1. Inner Oblique 2. Middle Circular 3. Outer Longitudinal Layers Sub Mucus Layer Areolar Tissue , Blood Vessels, Lymph Vessels and Meissner Nerve Plexus Inner Muscus layer Formed by Mucus Secreting Columnar Epithelial Cells. The Gastric Glands are situated in this layer
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  1. Fundic glandsor main gastric glands or oxyntic glands 2. Pyloric glands 3. Cardiac glands
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  Structure Of GastricGlands Fundic glands are considered as the typical gastric glands. These glands are long and tubular. Each gland has three parts, viz. body, neck and isthmus. Cells of fundic glands 1. Chief cells or pepsinogen cells 2. Parietal cells or oxyntic cells 3. Mucus neck cells 4. Enterochromaffin (EC) cells 5. Enterochromaffin like (ECL) cells.
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  Pyloric Glands Pyloric glandsare short and tortuous in nature. These glands are formed by G cells, mucus cells, EC cells and ECL cells. Cardiac Glands Cardiac glands are also short and tortuous in structure, with many mucus cells. EC cells, ECL cells and chief cells are also present in the cardiac glands Enteroendocrine Cells Enteroendocrine cells are the hormone secreting cells present in the glands or mucosa of gastrointestinal tract, particularly stomach and intestine. The enteroendocrine cells present in gastric glands are G cells, EC cells and ECL cells
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  PROPERTIES OF GASTRICJUICE Volume : 1200 mL/day to 1500 mL/day. Reaction : Gastric juice is highly acidic with a pH of 0.9 to 1.2. Acidity of gastric juice is due to the presence of hydrochloric acid. Specific gravity : 1.002 to 1.004
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  Secretion of GastricJuice SECRETION OF PEPSINOGEN Pepsinogen is synthesized from amino acids in the ribosomes attached to endoplasmic reticulum in chief cells. Pepsinogen molecules are packed into zymogen granules by Golgi apparatus. When zymogen granule is secreted into stomach from chief cells, the granule is dissolved and pepsinogen is released into gastric juice. Pepsinogen is activated into pepsin by hydrochloric acid.
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  Secretion of HydrochloricAcid ◦ According to Davenport theory, hydrochloric acid secretion is an active process that takes place in the canaliculi of parietal cells in gastric glands. The energy for this process is derived from oxidation of glucose. ◦ CO2 + H2O + NaCl → HCl + NaHCO3
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  Regulation of Gastric Secretion
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  CONTROL OF GASTRICACID SECRETION
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  CEPHALIC PHASE Secretion ofgastric juice by the stimuli arising from head region (Cephalus) is called cephalic phase which is regulated by nervous mechanism.
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  GASTRIC PHASE
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  ◦ Secretion ofgastric juice when food enters the stomach is called gastric phase. ◦ This phase is regulated by both nervous and hormonal control. ◦ Gastric juice secreted during this phase is rich in pepsinogen and hydrochloric acid.
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  ◦ Mechanisms involvedin gastric phase are: 1. Nervous mechanism through LOCAL MYENTERIC REFLEX AND VAGOVAGAL REFLEX 2. Hormonal mechanism through GASTRIN Stimuli, which initiate these two mechanisms are: • Distention of stomach • Mechanical stimulation of gastric mucosa by bulk of food • Chemical stimulation of gastric mucosa by the food contents.
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  NERVOUS MECHANISM LOCAL MYENTERICREFLEX ◦ Local myenteric reflex is the reflex elicited by stimulation of MYENTERIC NERVE PLEXUS in stomach wall. After entering stomach, the food particles stimulate the local nerve plexus present in the wall of the stomach. ◦ These nerve fibers release ACETYLCHOLINE, which stimulates the gastric glands to secrete a large quantity of gastric juice. ◦ Simultaneously, acetylcholine stimulates G cells to secrete gastrin VAGOVAGAL REFLEX AFFERENT AND EFFERENT VAGAL fibers.
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  HORMONE MECHANISM Gastrin isa gastrointestinal hormone secreted by the G cells which are present in the pyloric glands of stomach. Small amount of gastrin is also secreted in mucosa of upper small intestine. In fetus, it is also secreted by islets of Langerhans in pancreas. Gastrin is released when food enters stomach. Mechanism involved in the release of gastrin may be the local nervous reflex or vagovagal reflex.  Nerve endings release the neurotransmitter called gastrin releasing peptide, which stimulates the G cells to secrete gastrin.
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  ◦ Actions ofGastrin on gastric secretion : Gastrin stimulates the secretion of pepsinogen and hydrochloric acid by the gastric glands. ◦ Other Actions as follows : i. Stimulates gastric glands to secrete gastric juice with more pepsin and hydrochloric acid. ii. Accelerates gastric motility. iii. Promotes growth of gastric mucosa. iv. Stimulates secretion of pancreatic juice, which is rich in enzymes. v. Stimulates islets of Langerhans in pancreas to release pancreatic hormones.
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  INTESTINAL PHASE ◦ Intestinalphase is the secretion of gastric juice when chyme enters the intestine . There are two intestinal Phase : Initial Stage and Later Stage. INITIAL STAGE OF INTESTINAL PHASE ◦ Chyme that enters the intestine stimulates the duodenal mucosa to release gastrin, which is transported to stomach by blood. There it increases gastric secretion.
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  LAST STAGEOF INTEST INAL PHASE 1. Enterogastric reflex Enterogastric reflex inhibits the gastric secretion and motility. It is due to the distention of intestinal mucosa by chyme or chemical or osmotic irritation of intestinal mucosa by chemical substances in the chyme. It is mediated by myenteric nerve (Auerbach) plexus and vagus. 2. Gastrointestinal hormones Presence of chyme in the intestine stimulates the secretion of many GI hormones from intestinal mucosa and other structures. All these hormones inhibit the gastric secretion. Some of these hormones inhibit the gastric motility also.
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  GI hormones whichinhibit gastric secretion: i. Secretin: Secreted by the presence of acid chyme in the intestine ii. Cholecystokinin: Secreted by the presence of chyme containing fats and amino acids in intestine iii. Gastric inhibitory peptide (GIP): Secreted by the presence of chyme containing glucose and fats in the intestine iv. Vasoactive intestinal polypeptide (VIP): Secreted by the presence of acidic chyme in intestine v. Peptide YY: Secreted by the presence of fatty chyme in intestine.
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  Applied physiology ◦ GASTRITIS ◦GASTRICATROPY ◦PEPTIC ULCER ◦ZOLLINGER ELLISON SYNDROME
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  Thank you