The hormone gastrin is secreted by

The correct option is stomach.

Step-by-Step Explanation:

1. Understanding Gastrin:
Gastrin is a peptide hormone that plays a crucial role in the digestive system. Its primary function is to stimulate the parietal cells in the stomach to secrete gastric acid (hydrochloric acid or HCl), which is essential for digesting food and activating digestive enzymes like pepsinogen.

2. Site of Secretion:
Gastrin is synthesized and secreted mainly by specialized endocrine cells called G cells. These G cells are located in the mucosa of the antrum (the lower portion) of the stomach. Some gastrin is also secreted in the duodenum (the first part of the small intestine), but the primary and most significant site of secretion is the stomach.

3. Evaluating the Options:
- Pancreas: Primarily secretes insulin, glucagon, and pancreatic juices containing digestive enzymes, not gastrin under normal physiological conditions.
- Stomach: Contains the G cells in the pyloric antrum that are the primary source of gastrin secretion. Therefore, this is the correct organ.
- Liver: Produces bile and performs metabolic functions, but does not secrete gastrin.
- Intestine: While minor amounts of gastrin can be released by the duodenum, the primary and classic site of gastrin secretion is the stomach.

Thus, gastrin is primarily secreted by the stomach.