duodenum

This term refers specifically to the C-shaped initial section of the small intestine. It serves as the primary site for chemical digestion, where acidic chyme from the stomach is neutralized by bicarbonate and mixed with enzymes from the pancreas and bile from the gallbladder.

As a specialized anatomical term, it is used almost exclusively in medical, biological, and surgical contexts. It is a countable noun, though it is typically referred to in the singular since humans possess only one.