Where is enterokinase secreted from?

• A. Pancreas
• B. Brush border of small intestine
• C. Stomach
• D. Liver

Answer: (B)

Enterokinase is a brush-border enzyme of the small intestine. It sits on the luminal surface of enterocytes, mainly in the duodenum, where it activates pancreatic trypsinogen to trypsin. This initial activation step is required to start the cascade that activates other digestive proteases. It is not produced by the pancreas, stomach, or liver, which is why the brush border of the small intestine is the correct source.