After a period of fasting, gastric residue is all that remains in the stomach. This fluid can be removed via a tube inserted through the esophagus.
To test the capacity of the parietal cells in the stomach to secrete acid, gastrin may be injected subcutaneously (just under the skin), intramuscularly, or intravenously. The stomach contents are then removed and analyzed.
Another test involves insulin-induced hypoglycemia. Enough insulin is given subcutaneously or intravenously to cause the blood sugar to decrease, which causes the vagus nerve to stimulate the release of gastrin. After a short time, the stomach contents are removed and analyzed.
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