American Board of Pathology (ABPath) Practice Test

The correct answer is chymotrypsin, as it is not produced by the duodenum. Instead, chymotrypsin is an enzyme that is synthesized and secreted by the pancreas as a proenzyme (chymotrypsinogen) and then activated in the small intestine. Its primary function is to aid in the digestion of proteins.

In contrast, the duodenum plays a crucial role in the digestion and absorption processes. It secretes hormones such as cholecystokinin (CCK) and secretin, which are vital for regulating digestive enzyme secretion from the pancreas and bile release from the gallbladder. Additionally, acetylcholine is a neurotransmitter that is involved in stimulating digestive activities but is produced by neurons rather than the duodenum itself.

Thus, when considering the functions and origins of these substances, it is clear that chymotrypsin is the exception in this context, as it originates from the pancreatic secretions rather than being produced in the duodenum.