What is the characteristic of Zollinger-Ellison syndrome?

Zollinger-Ellison syndrome is primarily characterized by the production of gastrin-secreting tumors, known as gastrinomas, typically found in the pancreas or the duodenum. The overproduction of gastrin leads to excessive gastric acid secretion, which can cause recurrent peptic ulcers and other gastrointestinal symptoms. This syndrome is classified as a type of gastrin-secreting tumor disease, emphasizing the pivotal role of gastrin in its pathology.

In contrast, the other options relate to different endocrine disorders. Excessive cortisol production is associated with Cushing's syndrome, which involves adrenal tumors or hyperplasia. Excessive insulin secretion is characteristic of insulinomas or conditions like hypoglycemia and not related to Zollinger-Ellison syndrome. Large production of growth hormone pertains to acromegaly or gigantism, conditions resulting from growth hormone-secreting tumors typically in the pituitary gland. Therefore, the defining feature of Zollinger-Ellison syndrome is indeed the excessive production of gastrin.