Which gastric secretion is considered an intrinsic secretion because it is delivered directly to the bloodstream?

Gastrin is the secretion that is considered intrinsic because it is released directly into the bloodstream. It is a hormone produced by G cells in the gastric mucosa, particularly in the antrum of the stomach. Once released into the bloodstream, gastrin plays a key role in promoting gastric acid secretion by stimulating parietal cells in the stomach to produce hydrochloric acid (HCl) and by encouraging gastric motility.

In contrast, mucous, HCl, and pepsinogen are primarily considered extrinsic secretions because they are secreted into the lumen of the stomach rather than directly into the bloodstream. Mucous helps protect the gastric lining, HCl aids in digestion and creates an acidic environment, and pepsinogen is an inactive enzyme that converts to pepsin in the presence of acid for protein digestion. Thus, while all are important for digestion, gastrin's direct hormonal action in the bloodstream classifies it as an intrinsic secretion.