GI Flashcards
Briefly the urea breath test
Urea marked with a Carbon Isotope (usually 13 or 14) is ingested by the patient. Upon exhalation either mass spectrometry or scintillation will detect the isotope, indicating urea hydrolysis by urease in turn indication H.pylori infection.
What are four methods of detecting H.pylori infection other than the urea breath test?
- Biopsy/ histology
- Stool sample antigen
- Serology
- Micro culture(?)
What are their three principle stages of acid secretion?
Cephalic, gastric, intestinal.
Describe the cephalic phase of digestion.
The initial phase of gastric secretion caused by the site, smell or thought of food. It is more intense when you have been conditioned to a particular food (also known as Reflex Phase)
Describe the gastric phase of digestion.
Starts with the distention of stomach stretch receptors. Parasympathetic nerves release AcH which promotes the secretion of gastric juices.
A rising pH encourages the release of HCL, which cleaves pepsinogen to pepsin. HCL also leads to stomach contraction for movement of the bolus/ chyme.
Describe the intestinal phase of digestion.
Excitatory and inhibitory. Entry of chyme into the duodenum causes mucosal cells to release intestinal gastrin. Distention of the duodenum causes the entero-gastric reflex to close the pyloric sphincter. This mediates volume of food entering the duodenum.
Summarise H.pylori
Helicobacter pylori is a helical, gram -ve bacteria. May be commensal, and is asymptomatic amongst 80% of infections.
Colonisation of the pylorus by H.pylori can lead to chronic inflammation, hyper secretion of acid and ulceration of the gastric mucosa.
It survives acidic environments by the expression of urease, which promotes the production of ammonia which buffers acid.
Summarise Histamine 2 Receptor Antagonist action.
Therapeutic of upper GI disorders.
Binds H2R, which negates the effect of histamine secreted by ECL cells. The result is a reduced secretion of acid. Efficacy goers down over time.
Examples: Zantac (Ranitidine) or Tagamet (Cimetidine)
Summarise the action of Proton Pump Inhibitors.
Act on the final common pathway of acid section in parietal cells. The target is the proton pump H+/K+ATPase.
Migrate and concentrate in acidic vesicles of parietal cells, where they are protonated. Becoming highly reactive, they non-reversible bind to and denature proton pumps. No HCL can be synthesised.
95% efficacy. An example is omeprazole.
Give an example treatment regimen for a peptic ulcer caused by Helicobacter pylori.
Endoscopy, cauterisation, adrenaline injection. Fluid resus in case of severe blood loss.
Triple therapy consisting of:
Omeprazole (proton pump inhibitor)
Amoxicillin (Antibiotic), Clarithromycin (Antibiotic). - 8 weeks.
Urea Breath Test to monitor.
Give an example treatment regimen for a peptic ulcer caused by NSAID overuse.
Endoscopy, cauterisation, adrenaline injection. Fluid resus in case of severe blood loss.
Cessation of NSAID use.
Omeprazole (Proton Pump Inhibitor)
Misoprostiol (synthetic prostaglandin)
List the principle cell types in the stomach.
Simple columnar epithelium with:
Parietal Cells
Mucous Neck Cells
Parietal Cells
G Cells.
(D Cells, ECL Cells)
What are the two nerve plexuses of the stomach? (Superficial - deep).
Submucosal and mesenteric.
Which main artery serves the stomach?
Coeliac trunk.
What cell secretes Gastrin? What is its target? What are its effect?
Principally G Cells of the Pyloric Antrum in the presence of peptides and amino acids.
It targets the stomach (promotes gastric secretions), small intestine (peristalsis), ileocecal valve (relaxes the valve) and the large intestine (peristalsis).
