What is the primary hormonal secretion associated with carcinoid tumors leading to symptoms?

Carcinoid tumors are neuroendocrine tumors that most commonly arise in the gastrointestinal tract, particularly the small intestine. One of the hallmark features of these tumors is their ability to secrete serotonin, a neurotransmitter that plays various roles in the body, including the regulation of mood, appetite, and digestion.

The overproduction of serotonin by carcinoid tumors leads to a range of symptoms collectively known as the carcinoid syndrome. This syndrome is characterized by symptoms such as flushing of the skin, diarrhea, and wheezing, which occur due to the effects of excess serotonin on blood vessels and the gastrointestinal tract. In particular, serotonin can cause vasodilation, leading to flushing, and stimulates intestinal motility, causing diarrhea.

The other choices do not fit as primary hormonal secretions associated with carcinoid tumors. Epinephrine is associated with adrenal medullary function and is not secreted by carcinoid tumors. Cortisol is a steroid hormone secreted by the adrenal cortex, primarily involved in metabolism and the stress response. Insulin, produced by the pancreas, regulates glucose metabolism and does not play a significant role in the pathology of carcinoid tumors.

Thus, serotonin is the primary hormone that causes the characteristic symptoms of carc