L3*-Secretions of the stomach Flashcards
(15 cards)
Name 4 functions of the stomach
-secretions - different cell types
-motility - paralysis
-digestion - carbohydrate, protein, fat
-Absorption
What does the ingested food enter the stomach THROUGH?
Ingested food (now BOLUS) enter the stomach through the lower oesophageal sphincter.
Describe the anatomy of the stomach in brief terms.
-Cardia = near gastroesophageal sphincter, top part of cardia is for storage, bottom part is for enhancing digestion.
-Oxyntic mucosa = fundus and body
- pyloric = antrum(has a larger pit to secrete more mucus) and pyloric sphincter
Lumen of the stomach is covered by 7 types of cells. Name them and what they secrete into the stomach.
-Mucous > mucous
-Neck cell > Bicarbonate
-Parietal cell > acid and intrinsic factor
-EC like cell > Histamine
-Chief cell > Pepsinogen & lipase
-D cell > Somatostatin
-G cell > Gastrin
Name 4 gastric secretions by the stomach lining to aid digestion.
1). HCl
2). Pepsin
3). Mucus
4). Intrinsic factor(IF)
Describe the steps for acid secretion by parietal cells. 1).HCl
- Cl- transported from the cytoplasm of the parietal cells into the lumen.
- Na+ transported from the canaliculus(deep folding in the membrane of the parietal cell) into the cytoplasm of the parietal cell.
- Water dissociates into H+ and OH- in the cytoplasm of the cell.
- The H+ are secreted into the canaliculus in exchange for K+.
- CO2 combines with OH- to form bicarbonate ions (HCO3-) using carbonic anhydrase.
*CA is an antiporter so more Cl- comes in. - HCO3- diffuse out of the cell cytoplasm into the extracellular fluid in exchange for Cl- (alkaline tide).
- Na goes into help Cl- diffuse in. Na+ later then exits the membrane, through Na+K+ pump.
What regulates acid secretion? 1)HCl
-Vagus nerve - indirect - Ac ton G cell by releasing gastrin releasing peptide 👉 secrete gastrin 👉 act on CCKB receptor of parietal cell 👉 👆se in HCL secretion
-Paracrine - Histamine - Act on H2 receptor of parietal cell👉 HCL secretion
What inhibits acid secretion ? NOT a 😔 thing bc need to inhibit acid secretion once food leaves the stomach.
-Enterogastrones: are hormones secreted by the duodenum that inhibits peristalsis and secretions in the stomach. The hormone is stimulated by fat.
Examples: Somatostatin, CCK, Prostaglandins and Secretin.
- Secretin: (released by S cells in duodenum) stimulated by fat and acid in duodenum can inhibit acid secretion, by inhibiting Antral gastrin release and Somatostatin
release. - CCK is produced by I-cells of the duodenum and jejenum in response to fat. It directly reduces parietal-cell acid secretion.
- Proton pump inhibitors(Omeprazole): Direct action on the proton pump itself.
- H2 receptor antagonists (cimetidine & ranitidine)- old hat. The H2 antagonists are competitive antagonists of histamine at the
parietal cell H2 receptor. - Certain medications can inhibit the Na+K+ pump.
What are the 4 phases of Gastric(stomach) secretion ?
- Basal > Follows a circadian rhythm. Acid secretion is low (am) and high (pm).
- Cephalic (30% of acid secretion) >Initiated by smell, sight, taste, thought, and swallowing
of food. Mediated by Vagus nerve → acid secretion. - Gastric (50-60% of acid secretion) >
Stimulated by distention(swelling or expansion due to internal pressure 👆sing) of stomach
(mechanoreceptors) and partially digested proteins. (gastrin release). - Intestinal (5-10% of acid secretion) > Stimulated by digested peptides in proximal part of the small intestine (gastrin release from duodenal G cells).
2). Describe the function of Pepsin as a gastric secretion.
-Pepsin initiate protein digestion
-Pepsin is obtained from pepsinogen( secreted by chief cells)
-ACh is the major trigger for pepsinogen secretion.
-Interlinked with acid secretion bc of similar trigger (ACh) and resulting peptides trigger antral G-cell gastrin secretion.
3). Describe the function of mucus as a gastric secretion
- Thick mucus, which contains trapped bicarbonates (HCO3-), is secreted by mucus cells.
- The mucus layer formed, protects the stomach lumen from its harsh (acidic; pH < 1) contents.
- Prostaglandins are important in maintaining the mucosal diffusion barrier. They in part do this by inhibiting acid secretion, stimulating
HCO3- secretion and mucus secretion.
*? Importance of Prostaglandins exemplified by the effects of NSAIDS on gastric mucosa.
4). Describe the function of IF as a gastric secretion
-Intrinsic factor (IF) is produced by the parietal cells.
-Necessary for the absorption of vitamin B12 in terminal ileum.
- In the stomach, IF binds to vit. B12 in food and protects it from degradation by acid.
What is the outcome if parietal cells are damaged in terms of no IF produced?
-Damaged parietal cells → no IF produced → no vit. B12 → effect on red blood cells synthesis → Pernicious (megaloblastic) anaemia.
- Pernicious anaemia is an autoimmune atrophic gastritis, in which auto-antibodies are directed against parietal cells and results in their destruction.
Give details on the peptic ulcer
-Peptic ulcer is a open sore(break in the skin or the mucous membrane) that forms on the lining of the stomach or the upper part of the small intestine.
-Cause - Helicobacter pylori
-H.Plyori is an acid loving, gram -ve, bacteria that colonises the stomach of about 40% of humans.
-H.pylori causes acid production and barrier damage.
Treatment for peptic ulcer
-In the antrum, H. pylori infection causes G-cells to hypersecrete(more) gastrin and decrease antral D-cell somatostatin release → ↑ acid → hypergastrinemia → duodenal cancer.
-In the corpus, H. pylori infection leads to reduced acid secretion and Hypochlorhydria → gastric ulcers.
- Urease produced by HP converts
- Urea → NH3 + CO2+ H2O → NH4+ + HCO3- → neutralizes the stomach acid.
- Treatment-Triple therapy consisting of the antibiotics amoxicillin and clarithromycin, and a proton pump inhibitor.
👇
amoxicillin > destroys bacterial cell wall
clarithromycin > affect protein synthesis
proton pump inhibitor > 👇ses acid secretion
