Biochemical aspect of gastric secretions Flashcards
What is the action of pepsinogen?
Activated to pepsin via HCl which then digests proteins into amino acids or dipeptides)
What are the main constituents of the gastric secretions?
1) HCl (Secreted by the parietal cells, triggered by gastrin)
2) Pepsinogen (secreted by the chief cells)
3) Intrinsic factor “glycoproteins” (required for B12 absorption)
4) Alkaline mucous (secreted by the mucous cells, it coats the gastric cells and acts as a lubricant)
- Sometimes bile can be present
What are the causes of hyposecretion of the gastric juices?
1) Pernicious anemia (immunological disorder where the antibodies attacks the intrinsic factor proteins, cells)
2) Extensive carcinoma in the stomach
3) Chronic gastritis
- However in such cases gastrin levels are increased due to the reduced acid secretion (as a feed-back mechanism)
What are the different conditions of the stomach that can be investigated using biochemistry?
1) Gastroesophageal reflux disease
2) Peptic ulcer
3) Vitamin B12 deficiency
4) Gastrinomas (Zollinger ellison syndrome)
5) Effectiveness of vagotomy
What is GERD?
- Acid reflux
- It is the backflow of the acid and the stomach contents into the esophagus, which can lead to the irritation of the lining of the esophagus
- Common sign and symptoms include (heartburn “usually after eating and can be worse at night”, Chest pain, Difficulty swallowing, vomiting of food or a bitter taste, sensation of a lump in the throat), it might also cause chronic cough, disrupted sleep if there is night reflux
What are the different investigations that can be used to diagnose GERD?
1) pH monitoring
2) GI endoscopy & Manometry
How do we monitor the pH of a GERD patient?
- During fasting, we insert a naso-esophageal catheter that has a acid-sensitive tip
- The catheter is kept in the nose for 24-hours while the patient is living his normal life
- PPI, H2 blocker and antacids must be stopped
- An advanced method is a wireless pH testing (radiotelemetry pH sensing capsule)
What is meant by GI endoscopy?
Helpful to confirm the diagnosis of reflux by demonstrating the complication of reflux and it also helps in evaluating the anatomy if there is any mases or hernia
What is meant by GI manometry?
- Measures the pressure at the GI tract and the esophagus
- It evaluated the muscle and sphincter function, helping in the diagnosis of motility disorders and assessing the LES pressure for a possible surgery plan
What is a ulcer?
- A sore in the lining of the stomach, S.I or esophagus
- One of the main causes is helicobacter pylori infection
How does an infection with H.pylori causes peptic ulcer?
- Infection will deteriorate the stomach mucosal lining by causing inflammation which disrupts the mucous layer, allowing the HCl and pepsin to produce ulceration
- H.pylori can produce urease, which hydrolyze urea (diffused from the blood “produced from the catabolism of amino acids (urea cycle in the liver”), and then secreted in the urine) into ammonia and co2 and neutralizes acidity making the environment more favorable for H.pylori growth and infection
What are the different types of H.pylori tests?
1) Urea breath test
2) Serological helicobacter pylori IgG antibody
3) Faecal H.pylori antigen
What are the invasive method to test for H.pylori?
- Based on taking a biopsy by catheterization which is then analyzed by different procedures
1) Rapid urease test
2) Histology (use of microscope to detect the bacteria)
3) Culture and antimicrobial susceptibility testing
Describe the urea breath test
The patient is given urea but with the carbon part being an isotope (C13) along with a fruit drink or a capsule
- Breath sample is taken after 30 minutes
- High concentration of the labelled carbo isotope will indicate the presence of urease and thus H.pylori in the gastric mucosa
Describe the serological helicobacter pylori IgG antibody test
- This is an enzyme-linked immunosorbent assay (ELISA) which will detect IgG antibodies related to H.pylori from a blood, urine or sputum sample
Describe the fecal helicobacter pylori test
Sample of the feces is taken and we check the Prescence of H.pylori antigens in them
Describe the rapid urease test
- Biopsy from the gastric mucosa
- Add urea to the biopsy, and then if urease was present the pH would increase and thus using a pH-dependent color indicator we see its presence
What is gastrin?
- Released by the G-cells in the pyloric antrum, duodenum and the pancreas, gastrin is a peptide hormone which stimulates the secretion of gastric acid by the parietal cells, and it also aids in the gastric motility
- Gastrin release is inhibit when the pH of the stomach reaches 1
What is zollinger-Ellison syndrome?
It is a gastrin-secreting neoplasm located in the pancreatic islets (non-beta islet cells)
What are the different causes of hypersecretion of gastric acid?
1) Duodenal ulcers
2) Zollinger-ellison syndrome
What are the different causes for hyposecretion of gastric acid?
1) Enteric infections (Like e.coli, vibrio.cholers, etc)
2) Pernicious anemia
3) Atrophic gastritis
4) Gastric carcinoma
What are the types of gastric acid output?
1) Basal gastric acid output
2) Post stimulation (maximum acid output-MAO)
What are the different ways to measure basal gastric acid output?
- Represents the output of a fasting, unstimulated stomach
- Levels of BAO can fluctuate and it is obtained by aspiration of the gastric acid for an hour (4 times once every 15 min, from a fasted stomach)
- Overnight fast, Intubation, Collect secretion every 15 minutes for 1 hour as base line (base acid output)
Describe the maximum acid output test (post stimulation)
- Stomach is stimulated by a synthetic gastrin
- Collect gastric secretion every 15 minutes for 1 hour, after the administration of pentagastrin (synthetic gastrin)
- Then we measure the volume, pH, via titration and calculate the total acidity in the total volume for the basal and stimulated sample
- Pentagastrin stimulates the secretion of HCl
- Patient should be fasting and intubated
