Final answer:
The small intestine is responsible for secreting cholecystokinin (CCK), a hormone that assists in lipid digestion by stimulating the pancreas and gallbladder. The pancreas produces most of the fat-digesting enzymes.
Step-by-step explanation:
The structure that secretes cholecystokinin (CCK) is the small intestine. CCK is a hormone crucial for the digestive process, particularly in the digestion of fats. It stimulates the pancreas to release pancreatic lipase and the gallbladder to contract, releasing bile salts into the small intestine to aid in lipid digestion. Additionally, most fat-digesting enzymes are produced by the pancreas, which then secretes these enzymes into the small intestine to break down fats into smaller molecules that can be absorbed.