Gastrin works on the parietal cells of the gastric glands, causing them to secrete more hydrogen ions into the stomach lumen. In addition, gastrin acts as a trophic factor for parietal cells, causing parietal cell hyperplasia. Normally, hydrogen ion secretion is controlled by a negative feedback loop by gastric cells to maintain a suitable pH, however, the neuroendocrine tumor that is present in individuals with<unk>  has no regulation, resulting in excessively large amounts of secretion. Thus, there is an increase in the number of acid-secreting cells, and each of these cells produces acid at a higher rate. The increase in acidity contributes to the development of peptic ulcers in the stomach, duodenum (first portion of the small bowel) and occasionally the jejunum (second portion of the small bowel), the last of which is an 'atypical' ulcer.
Zollinger–Ellison syndrome
Toriello–Carey syndrome
Naegeli–Franceschetti–Jadassohn syndrome
Johanson–Blizzard syndrome
Meigs's syndrome
Whipple's disease
HIDEA syndrome
Löffler's syndrome