Nasolacrimal duct

Nasolacrimal duct

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The nasolacrimal duct carries tears
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....

 from the lacrimal sac
Lacrimal sac
The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla...

 into the nasal cavity
Nasal cavity
The nasal cavity is a large air filled space above and behind the nose in the middle of the face.- Function :The nasal cavity conditions the air to be received by the other areas of the respiratory tract...

. Excess tears flow through nasolacrimal duct which drains into the inferior nasal meatus. This is the reason the nose starts to run when a person is crying or has watery eyes from an allergy, and why one can sometimes taste eye drops.

Like the lacrimal sac, the duct is lined by stratified columnar epithelium
Stratified columnar epithelium
Stratified columnar epithelia is a rare type of epithelial tissue composed of column shaped cells arranged in multiple layers.Stratified columnar epithelia are found in the ocular conjunctiva of the eye, in parts of the pharynx and anus, the female's uterus, the male urethra and vas deferens...

 containing mucus-secreting goblet cells, and is surrounded by connective tissue.

Obstruction of the nasolacrimal duct, known as dacryostenosis, leads to the excess overflow of tears called epiphora
Epiphora (medical)
Epiphora is overflow of tears onto the face. A clinical sign or condition that constitutes insufficient tear film drainage from the eyes in that tears will drain down the face rather than through the nasolacrimal system.-Etiology:...

. A congenital obstruction can cause cystic expansion of the duct and is called a dacrocystocele
Dacrocystocele
A dacryocystocele is a benign, bluish-gray mass in the inferomedial canthus that forms as a result of a narrowing or obstruction of the nasolacrimal duct, usually during prenatal development....

 or Timo cyst. Persons with dry eye conditions can be fitted with punctal plug
Punctal plug
A punctal plug is a small medical device that is inserted into the tear duct of an eye to block the duct. This prevents the drainage of liquid from the eye. They are used to treat dry eye....

s that seal the ducts to limit the amount of fluid drainage and retain moisture.

The canal containing the nasolacrimal duct is called the nasolacrimal canal
Nasolacrimal canal
The canal containing the nasolacrimal duct is called the nasolacrimal canal.It is formed by indentations in the inferior nasal conchae, maxilla and lacrimal bone...

.