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 th ...

of the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

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 nas ...

. The duct begins in the

eye socket In anatomy, the orbit is the cavity or socket/hole 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 ...

between the

maxilla In vertebrates, the maxilla (: maxillae ) 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 two maxil ...

ry and

lacrimal bone The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...

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 physical pain. Emotions that can lead to crying include sadness, anger, joy, and fear. Crying can also be caused by relief from a period ...

or has watery eyes from an allergy, and why one can sometimes taste eye drops. 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 Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin 2 in the lower gastrointestinal tract, and mucin 5AC in the respiratory tract. The goblet cells mainly use the merocrine method of secretion, secreting ...

, and is surrounded by connective tissue.

Nasolacrimal canal

The canal containing the duct is called the nasolacrimal canal. It is formed by indentations in the

inferior nasal concha The inferior nasal concha (inferior turbinated bone or inferior turbinal/turbinate) is one of the three paired nasal conchae in the human nose, nose. It extends horizontally along the lateral wall of the nasal cavity and consists of a wikt:lam ...

and

. The canal drains into the

through the anterior portion of the

inferior 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 ...

, which is between the inferior concha and the floor of the nasal cavity.

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 or ''Timo cyst''. Persons with dry eye conditions can be fitted with

punctal plug A punctal plug, also known as tear duct plug or lacrimal plug, is a small medical device that is inserted into the Nasolacrimal duct, tear duct (puncta) of an human eye, eye to block the duct. This prevents the drainage of liquid from the eye. They ...

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

infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

, excess mucus may drain through the nasolacrimal duct in the opposite way tears drain. In

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

, 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'' (''WSJ''), also referred to simply as the ''Journal,'' is an American newspaper based in New York City. The newspaper provides extensive coverage of news, especially business and finance. It operates on a subscriptio ...

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

Fox News The Fox News Channel (FNC), commonly known as Fox News, is an American Multinational corporation, multinational Conservatism in the United States, conservative List of news television channels, news and political commentary Television stati ...

, May 5, 2011.

Additional image

Image:Gray196.png, Roof, floor, and lateral wall of left nasal cavity File:Orbital bones.png, The seven bones which articulate to form the orbit. File:Gray1199.png, Outline of bones of face, showing position of air sinuses.

References

External links

* * - "Orbits and Eye: Orbital openings and related anatomical features" * {{DEFAULTSORT:Nasolacrimal Duct Human eye anatomy

Nasolacrimal canal

Clinical significance

Additional image

See also

References

External links