Final answer:
Cholecystokinin (CCK) is the hormone that is released when fats are present in the small intestine, leading to gallbladder contraction and the release of bile salts, as well as stimulating the production of pancreatic lipase.
Step-by-step explanation:
The hormone released in response to fats in the small intestine, which stimulates gallbladder contraction, is cholecystokinin (CCK). The presence of fat in the chyme in the small intestine triggers the intestinal mucosa to release CCK. In turn, CCK stimulates the contraction of the gallbladder, resulting in the release of stored bile salts into the intestine. Furthermore, CCK aids in lipid metabolism by stimulating the release of pancreatic lipase from the pancreas, which is crucial for breaking down fats into smaller molecules that the body can absorb.