Complex sentence: When the pancreas is stimulated by cholecystokinin, It is then secreted into the small intestine, where the enzyme enteropeptidase activates it into trypsin by proteolytic cleavage.
Split into simpler sentences: When the pancreas is stimulated by cholecystokinin, it is then secreted into the small intestine. Once in the small intestine, the enzyme enteropeptidase activates it into trypsin by proteolytic cleavage.