Gastric function tests Flashcards
Gastrin
Peptide hormone that stimulates secretion of gastric juice (HCl) from the walls of the stomach
What secretes gastrin
gastric antrum mucosa (G cells) in response to food in stomach or smell, sight, thoughts e.t.c of food
Two ways the body regulates stomach acid secretion
Gastrin (negative feedback loop)
Histamines (most potent method)
Components of gastric juice
Water: 97 - 99%
HCL
Organic constituents
Inorganic constituents
What are the organic constituents of gastric juice
Rennin, pepsin, intrinsic factor, mucin, gastric lipase, albumin and globulin
Inorganic constituents of gastric juice
Sulphate, phosphate, sodium, calcium, potassium, magnesium, chloride
Ph of gastric juice
1.0 - 1.5
Color of gastric juice
Colourless-grey
Normal volume of gastric juice
2 - 4 litres per day
Cells of the gastric mucosa
Parietal cells (secretes HCl)
Chief cells (secretes enzymes)
Surface epithelial cells (secretes mucus)
Uses of gastric function tests
For creating suitable therapies for different gastro-oesophageal diseases
For drug development and delivery
For disease diagnoses
Stimulants of gastric juice production
Oatmeal
Tea and toast
7% alcohol
Histamines
Pentagastrin
Four main gastric function tests
Examination of resting content
Fractional gastric analysis using test meals
Examination of content after stimulation
Tubeless gastric analysis
Procedure for examination of resting content
After an overnight fast, the contents of the stomach are aspirated using a size 14 Ryle’s tube and a syringe. This is analyzed for different qualities for diagnoses of diseases
What qualities are the resting contents analyzed for
Volume
Consistency
Color
Mucus
Bile
Blood
Free and total acidity
Organic acids
Resting content- volume
Normal is between 20 - 50 ml
More can be caused by 3 factors- Overproduction of gastric juice, Slow gastric clearance, regurgitation from duodenum
Resting content- consistency
Normal is fluid-like with no food particles. May contain small amounts of mucus.
Presence of food particles are indicative of gastric carcinomas
Resting contents - colour
Normal is usually colourless. May be slightly green or yellow due to regurgitation of duodenal bile.
Red or brown colour is indicative of bleeding and may be present as a result of trauma, carcinomas or ulcers.
Resting content- mucus
Mucus is usually found in small amounts.
Large amounts may be indicative of gastric carcinomas, excess mucus swallowed from saliva and low HCl secretion.
Resting content - blood
Blood is not normal and may be present as a result of trauma, carcinomas or ulcers.
Resting content - bile
Bile may be present in small amounts due to duodenal regurgitation.
Large amounts are indicative of intestinal obstruction or ileal stasis
Resting content - Organic acids
A large amount of organic acids such as lactic and butyric acid are indicative of low gastric juice secretion (Achlorhydria and hypochlorhydria) as it is not sufficient to destroy the micro-organisms present and they end up fermenting the food. This is indicative of carcinomas.
Resting contents- Free and total acidity
Estimated by titration using NaOH. Methyl orange or phenolphthalein as indicators (yellow to red to signify endpoint)
Free acidity is the amount of HCl present
Total acidity is the free acidity plus the amount of organic acid present
Normal free acidity is 0 - 30mEq/L
Normal total acidity is 10 - 40 mEq/L
Procedure for fractional gastric analysis using test meals
Ingestion of test meal and 5-6 ml of gastric content is collected immediately after, using a Ryle’s tube and syringe
Then more 10ml samples are collected at 15 minute intervals.
If the stomach is not cleared after 3 hours, the entire stomach content is aspirated and the volume measured.
Each sample is filtered and the filtrate is analyzed for free and total acidity. The residue is checked for blood, starch, bile and mucus
Normal results of fractional gastric analysis
In normal health, free acid is found about 15-45 minutes after test meal ingestion. It then rises steadily to maximum at around 60mins to one and a half hours. At maximum, free acid is around 15 - 45 mEq/L and total acidity is usually 10 units higher. No blood, small amount of bile
Clinical significance of results of fractional gastric analysis
Hyperchlorhydria: Free acidity is higher than 45mEq/L. Found in gastric, duodenal, jejunal, gastro-jejunal ulcers and gastric carcinomas
Hypochlorhydria: Low acidity. Found in gastric carcinoma and atonic dyspepsia. Free HCl absent in pernicious anemia.
Achlorhydria: No free Hcl, pepsin is present in gastric secretion
Achylia gastrica: No gastric secretion at all
4 tests that fall under gastric stimulation test
Standard histamine stimulation test
Augmented histamine stimulation test
Insulin stimulation test
Pentagastrin stimulation test
Standard histamine stimulation test procedure
Stomach contents are aspirated after overnight fast and analyzed
0.01 mg/kg body weight histamine is administered subcutaneously, then 10 ml of stomach contents are aspirated periodically, every 10 minutes for an hour. These samples are analyzed for free and total acidity, peptic activity and presence of blood, bile and mucus
Standard histamine stimulation test result interpretation
No free HCl is indicative of achylia gastrica
More juice is secreted in duodenal ulcer
Augmented histamine stimulation test procedure
Overnight fast, stomach contents are aspirated at 20 mins intervals for an hour for analysis. At half this time, 4ml anthisan is injected intramuscularly
At the end of this hour, histamine is injected (0.04mg/kg body weight) subcutaneously and the stomach contents are aspirated at 15 mins intervals for an hour for analysis
Augmented histamine stimulation test result interpretation
No free acid produced in pernicious anemia
Higher acid seen in duodenal ulcer.
Insulin stimulation test procedure
Blood sugar must be below 45mg% to get reliable results
Overnight fast, stomach is emptied.
15 units of soluble insulin is injected intravenously and 10ml of stomach content is collected at 15mins intervals for 2 and a half hours. The contents are analysed for free and total acidity, peptic activity, blood, bile and starch. Starch should not be present.
Insulin stimulation test result interpretation
Duodenal ulcer means more acid is produced
Pentagastrin stimulation test procedure
Overnight fast, stomach is cleared
Basal secretion is obtained via two 15mins interval samples
Pentagastrin is injected subcutaneously and samples are collected over 15 mins intervals for an hou
Pentagastrin stimulation test result interpretation
Normal basal secretion rate is 1 - 2.5 mEq/hour
After pentagastrin injection, 20 - 40 mEq/hour
In duodenal ulcer, increase after pentagastrin is between 15 - 83 mEq/hr
Zollinger-Ellison syndrome presents with higher basal rate and no change with pentagastrin injection.
Tubeless gastric analysis
DiagnexBlue is administered. This contains Azur A, an indicator. When acted on by stomach acid, this indicator is released and shows up in the urine. The released amount is then matched with a standard to get the result.
Useful as a screening test only as negative does not signify true achlorhydria.
