The nasolacrimal duct (also called the tear duct) carries

tears Tears are a clear liquid secreted by the lacrimal glands (tear gland) found in the eyes of all land mammals. Tears are made up of water, electrolytes, proteins, lipids, and mucins that form layers on the surface of eyes. The different types of ...

from the

lacrimal sac The lacrimal sac or lachrymal 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. It connects the lacrimal canaliculi, which drain tears from the ...

of the eye into the

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal c ...

. The duct begins in the

eye socket In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is , of ...

between the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

ry and

lacrimal bone The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders. Several bony landmarks of ...

s, from where it passes downwards and backwards. The opening of the nasolacrimal duct into the inferior

nasal meatus In anatomy, the term nasal meatus can refer to any of the three meatuses (passages) through the skulls nasal cavity: the superior meatus (''meatus nasi superior''), middle meatus (''meatus nasi medius''), and inferior meatus (''meatus nasi inferio ...

of the nasal cavity is partially covered by a mucosal fold ( valve of Hasner or ''plica lacrimalis''). Excess tears flow through the nasolacrimal duct which drains into the inferior nasal meatus. This is the reason the nose starts to run when a person is

crying Crying is the dropping of tears (or welling of tears in the eyes) in response to an emotional state, or pain. Emotions that can lead to crying include sadness, anger, and even happiness. The act of crying has been defined as "a complex secr ...

or has watery eyes from an allergy, and why one can sometimes taste

eye drops Eye drops or eyedrops are liquid drops applied directly to the surface of the eye usually in small amounts such as a single drop or a few drops. Eye drops usually contain saline to match the salinity of the eye. Drops containing only saline ...

. This is for the same reason when applying some eye drops it is often advised to close the nasolacrimal duct by pressing it with a finger to prevent the medicine from escaping the eye and having unwanted side effects elsewhere in the body as it will proceed through the canal to the Nasal Cavity. Like the lacrimal sac, the duct is lined by

stratified columnar epithelium Stratified columnar epithelium is a rare type of epithelial tissue composed of column-shaped cells arranged in multiple layers. It is found in the conjunctiva, pharynx, anus, and male urethra. It also occurs in embryo. Location Stratified col ...

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

Clinical significance

Obstruction of the nasolacrimal duct may occur. This leads to the excess overflow of tears called '' epiphora'' (chronic low-grade nasolacrimal duct occlusion). A congenital obstruction can cause cystic expansion of the duct and is called a

dacryocystocele Dacryocystocele (Dacryocystitis) or timo cyst is a benign, bluish-gray mass in the inferomedial canthus that develops within a few days or weeks after birth. The uncommon condition forms as a result as a consequence of narrowing or obstruction of t ...

or ''Timo cyst''. Persons with dry eye conditions can be fitted with punctal plugs that seal the ducts to limit the amount of fluid drainage and retain moisture. During an ear infection, excess mucus may drain through the nasolacrimal duct in the opposite way tears drain. The canal containing the nasolacrimal duct is called the nasolacrimal canal. In

humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

, the tear ducts in males tend to be larger than the ones in females."Tears of Men and Women Are Different"
''

Wall Street Journal ''The Wall Street Journal'' is an American business-focused, international daily newspaper based in New York City, with international editions also available in Chinese and Japanese. The ''Journal'', along with its Asian editions, is published ...

'', mirrored a
"Why Men and Women Shed Different Tears"

Fox News The Fox News Channel, abbreviated FNC, commonly known as Fox News, and stylized in all caps, is an American multinational conservative cable news television channel based in New York City. It is owned by Fox News Media, which itself is owne ...

, May 5, 2011.

Additional images

Image:Gray196.png, Roof, floor, and lateral wall of left nasal cavity

References

External links

* * {{DEFAULTSORT:Nasolacrimal Duct Human eye anatomy

Clinical significance

Additional images

See also

References

External links