The nasolacrimal duct (also called tear duct, latin: ductus nasolacrimalis) is a channel that is directly continuous with the lacrimal sac and opens into the nasal cavity, forming the final part of the tear drainage system of the lacrimal apparatus.
The nasolacrimal duct is about 1.2 to 2.4 cm long. It passes through the nasolacrimal canal, which is formed by the lacrimal bone and maxilla, and opens into the inferior nasal meatus of the nasal cavity with an opening - the aperture of the nasolacrimal duct. The aperture is located beneath the inferior nasal concha and provided with a flap-like mucosal fold that partly covers it called the lacrimal fold, also known as the valve of Hasner.
The membranous wall of the nasolacrimal duct consists of connective tissue and stratified columnar epithelium. The flattened lumen of the nasolacrimal duct is lined by a mucous membrane containing two or more layers of columnar epithelium that has cilia at some sites and also contains mucous-secreting goblet cells.
The nasolacrimal duct drains excess tears from the nasolacrimal sac into the nasal cavity, which explains the phenomenon of a running nose when a person is crying.