Ductus: A duct or walled passageway suitable for the conveyance of air or, more often in the body, liquids.
The term "ductus" also refers a key arterial shunt (ductus) in fetal life. Before birth, blood pumped from the heart through the pulmonary artery toward the lungs is shunted into the aorta. This arterial shunt, a short vessel, is the ductus arteriosus. When the shunt is open, it is said to be patent. The ductus arteriosus usually closes at or shortly after birth, permitting blood from that moment on to course from the heart directly to the lungs. However, if the ductus arteriosus remains open (patent), flow reverses and blood from the aorta is shunted into the pulmonary artery and recirculated through the lungs. A patent ductus may close later spontaneously (on its own) or need to be ligated (tied off) surgically.
Our word "duct" is a contraction of the Latin word "ductus" meaning "leading". The Romans, however, preferred the word "canalis" meaning "a pipe or gutter" for a conduit.