The lacrimal apparatus is the physiological system containing the
orbital structures for
tear production and drainage.
[Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company, 1990.] It consists of:
* The
lacrimal gland
The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each or ...
, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the
human eye; it is a j-shaped serous gland located in lacrimal fossa.
* The
lacrimal canaliculi, 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 ...
, and the
nasolacrimal duct
The nasolacrimal duct (also called the tear duct) carries tears from the lacrimal sac of the eye into the nasal cavity. The duct begins in the eye socket between the maxillary and lacrimal bones, from where it passes downwards and backwards. T ...
, by which the fluid is conveyed into the cavity of the
nose
A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes ...
, emptying anterioinferiorly to the
inferior nasal conchae from the nasolacrimal duct;
* The
innervation of the lacrimal apparatus involves both the a
sympathetic supply through the
carotid plexus of nerves around the internal carotid artery, and
parasympathetically from the
lacrimal nucleus of the
facial nerve
The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste ...
.
The blood supply to the lacrimal gland is provided by the ophthalmic artery with its branch - the lacrimal artery, while the venous blood is drained from this region via the superior ophthalmic vein. The
lacrimal system is made up of a secretory system, which produces tears, and an excretory system, which drains the tears. The lacrimal gland is primarily responsible for producing emotional or reflexive tears. As tears are produced, some fluid evaporates between blinks, and some is drained through the
lacrimal punctum
The lacrimal punctum (plural ''puncta'') or lacrimal point, is a minute opening on the summits of the lacrimal papillae, seen on the margins of the eyelids at the lateral extremity of the lacrimal lake. There are two lacrimal puncta in the medial ...
. The tears that are drained through the punctum will eventually be drained through the nose. Any excess fluid that did not go into the punctum will fall over the eyelid, which produces tears that are cried.
References
External links
Diagram at hixie.ch
Human eye anatomy
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