Digestive Enzymes and Hormones: Functions and Roles in Human GI Tract

Gastrin

Stimulates parietal cells to release HCl, which lowers stomach pH and helps activate pepsinogen; increases stomach motility

Secretin

Released when acidic chyme enters small intestine; stimulates pancreas to secrete bicarbonate-rich fluid to neutralize acid so intestinal enzymes can work. Also dilutes chyme

CCK

Released in response to fats/proteins; stimulates pancreas to release digestive enzymes and gallbladder to release bile for fat digestion. Also dilutes chyme

Pepsin

Breaks large proteins into smaller peptides in acidic stomach environment

Salivary amylase

Begins starch digestion in mouth by breaking polysaccharides into maltose/shorter sugars

Pancreatic amylase

Continues carbohydrate digestion in small intestine, converting starch to maltose/oligosaccharides

Trypsin

Digests proteins into smaller peptides; also activates other pancreatic proteases

Chymotrypsin

Breaks peptide bonds in proteins, especially near aromatic amino acids

Carboxypeptidase

Removes amino acids one at a time from the carboxyl end of peptides

Pancreatic lipase

Breaks triglycerides into monoglycerides + free fatty acids for absorption

Lysozyme

Breaks bacterial cell walls in food, helping protect GI tract from microbes

Perforin

Not digestive; helps immune cells destroy infected/abnormal cells in gut tissues