The Stomach Flashcards
What are the two patterns of motility of the stomach?
Receptive relaxation - as food travels down the oesophagus, a neural reflex carried out by the vagus nerve triggers the relaxation of muscle in the stomach’s wall so pressure doesnt increase as it fills - preventing reflux - and allowing us to consume large meals
Rhythmic contractions - the stomach has longitudinal and circular muscle that is driven by a pacemaker in the cardiac region.
The pacemaker fires 3 times per minute causing regular, accelerating peristaltic contractions from cardia to pylorus.
These contractions + the stomach’s funnel shape mixes the contents of the stomach and the accelerating peristaltic waves move liquid chyme into the pyloric region as the waves overtakes the larger lumps, driving them back to the fundus.
What happens to the process of ingestion and digestion with damage to vagus nerve
Lost of neural reflex causing stomach to relax means that we lose the ability to consume large meals - reflux problems
What is the process of gastric emptying?
Chyme enters the pyloric region and a small squirt is ejected before the peristaltic wave reaches the pylorus and shuts it, so the rest of the chyme returns to the stomach.
How is the process of gastric emptying controlled?
Three peristaltic waves lead to three ejected squirts of chyme per minute - the volume of which is affected by rate of acceleration of peristaltic wave and hormones from the intestine.
Gastric emptying is slowed by fat, low pH and hypertonicity in the DUODENUM
What is gastric emptying slow be?
Fat, low pH and hypertonicity in the duodenum
What are the functions of the stomach’s defences? Why are they needed?
To protect mucosa from luminal pH of 2 which would otherwise dissolve.
Defences include mucus which is secreted by neck cells, and forms an unstirred layer through which ions cannot move through easily. H+ ions slowly diffuse in and react with basic groups on mucus and with HCO3- that is also secreted by the neck cells.
What is the pH of the surface cells and how is this achieved?
ph>6 due to unstirred layer, so HCO3- stays close to the surface cells.
What stimulates mucus and HCO3- secretion
Prostaglandins -> neck cells: mucus, and HCO3-
What substances/organisms can breach stomahc’s defences
Alcohol - dissolves mucus allowing the acid to attack the stomach
H. pylori infect surface cells inhibiting mucous and HCO3- production
NSAIDs inhibit prostaglandins, reducing defences but some NSAIDs like asipirin are converted to a non-ionised form by stomach acid, allowing them to pass through the mucus layer into cells before they re-ionise
Why does aspirin not affect the stomach’s defences
It gets converted into a non-ionised form by the stomach acid allowing it to diffuse through the mucus layer into cells before re-ionisation occurs
What results with breach of the stomach’s defences. Treatment?
Peptic ulcers - treat by reducing acid secretion and if present, eliminate H. pylori infection with triple therapy
What is the triple therapy treatment for H. Pylori infection
PPI - omeprazole, amoxicillin, clarithromycin
Pharmacologically, how can we reduce acid production?
PPI - omeprazole - inhibits proton pumps in canaliculi of parietal cells so that H+ can not be pumped out of cells
H2 antagonists - Cimetidine – removes the amplification of Gastrin/Ach signal usually provided by histamine
What are the 3 phases of control of gastric secretion
cephalic, gastric and intestinal
What is the cephalic phase
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