<Li> Acinar cells: Mainly responsible for production of the inactive pancreatic enzymes (zymogens) that, once present in the small bowel, become activated and perform their major digestive functions by breaking down proteins, fat, and DNA / RNA . Acinar cells are stimulated by cholecystokinin (CCK), which is a hormone / neurotransmitter produced by the intestinal cells (I cells) in the duodenum . CCK stimulates production of the pancreatic zymogens . </Li> <P> Pancreatic juice, composed of the secretions of both ductal and acinar cells, is made up of the following digestive enzymes: </P> <Ul> <Li> Trypsinogen, which is an inactive (zymogenic) protease that, once activated in the duodenum into trypsin, breaks down proteins at the basic amino acids . Trypsinogen is activated via the duodenal enzyme enterokinase into its active form trypsin . </Li> <Li> Chymotrypsinogen, which is an inactive (zymogenic) protease that, once activated by duodenal enterokinase, turns into chymotrypsin and breaks down proteins at their aromatic amino acids . Chymotrypsinogen can also be activated by trypsin . </Li> <Li> Carboxypeptidase, which is a protease that takes off the terminal amino acid group from a protein </Li> <Li> Several elastases that degrade the protein elastin and some other proteins . </Li> <Li> Pancreatic lipase that degrades triglycerides into fatty acids and glycerol . </Li> <Li> Sterol esterase </Li> <Li> Phospholipase </Li> <Li> Several nucleases that degrade nucleic acids, like DNAase and RNAase </Li> <Li> Pancreatic amylase that breaks down starch and glycogen which are alpha - linked glucose polymers . Humans lack the cellulases to digest the carbohydrate cellulose which is a beta - linked glucose polymer . </Li> </Ul> <Li> Trypsinogen, which is an inactive (zymogenic) protease that, once activated in the duodenum into trypsin, breaks down proteins at the basic amino acids . Trypsinogen is activated via the duodenal enzyme enterokinase into its active form trypsin . </Li>

Each of the following is an example of mechanical digestion except