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Lacrimal gland

Exocrine gland, one for each eye, that secrete tears

Summary

Exocrine gland, one for each eye, that secrete tears

Field	Value
Name	Lacrimal gland
Latin	glandula lacrimalis
Image	Gray896.png
Caption	Lacrimal apparatus of the right eye. The lacrimal gland is to the upper left. The right side of the picture is towards the nose.
Image2	Tear system.svg
Caption2	Tear system.
a = lacrimal gland
b = superior lacrimal punctum
c = superior lacrimal canal
d = lacrimal sac
e = inferior lacrimal punctum
f = inferior lacrimal canal
g = nasolacrimal canal
Artery	Lacrimal artery
Vein	Superior ophthalmic vein
Nerve	Lacrimal nerve

a = lacrimal gland b = superior lacrimal punctum c = superior lacrimal canal d = lacrimal sac e = inferior lacrimal punctum f = inferior lacrimal canal g = nasolacrimal canal The lacrimal glands (American) or lachrymal glands (English) 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 orbit, in the lacrimal fossa of the orbit formed by the frontal bone. Inflammation of the lacrimal glands is called dacryoadenitis. The lacrimal gland produces tears which are secreted by the lacrimal ducts, and flow over the ocular surface, and then into canals that connect to the lacrimal sac. From that sac, the tears drain through the lacrimal duct into the nose.

Anatomists divide the gland into two sections, a palpebral lobe, or portion, and an orbital lobe or portion. The smaller palpebral lobe lies close to the eye, along the inner surface of the eyelid; if the upper eyelid is everted, the palpebral portion can be seen.

The orbital lobe of the gland, contains fine interlobular ducts that connect the orbital lobe and the palpebral lobe. They unite to form three to five main secretory ducts, joining five to seven ducts in the palpebral portion before the secreted fluid may enter on the surface of the eye. Tears secreted collect in the fornix conjunctiva of the upper lid, and pass over the eye surface to the lacrimal puncta, small holes found at the inner corner of the eyelids. These pass the tears through the lacrimal canaliculi on to the lacrimal sac, in turn to the nasolacrimal duct, which dumps them out into the nose.

Lacrimal glands are also present in other mammals, including horses.

Structure

Histology

The lacrimal gland is a compound tubuloacinar gland, it is made up of many lobules separated by connective tissue, each lobule contains many acini. The acini composed of large serous cells which, produce a watery serous secretion, serous cells are filled with lightly stained secretory granules and surrounded by well-developed myoepithelial cells and a sparse, vascular stroma. Each acinus consists of a grape-like mass of lacrimal gland cells with their apices pointed to a central lumen.

The central lumen of many of the units converge to form intralobular ducts, and then they unite to form interlobular ducts. The gland lacks striated ducts.

Blood supply

The lacrimal gland receives blood from the lacrimal artery, which is a branch of the ophthalmic artery. Blood from the gland drains to the superior ophthalmic vein.

Lymphatic drainage

No lymphatic vessels have been observed draining the lacrimal gland.

Nerve supply

The lacrimal gland is innervated by the lacrimal nerve, which is the smallest branch of the ophthalmic nerve, itself a branch of the trigeminal nerve (CN V). After the lacrimal nerve branches from the ophthalmic nerve it receives a communicating branch from the zygomatic nerve. This communicating branch carries postganglionic parasympathetic axons from the pterygopalatine ganglion. The lacrimal nerve passes anteriorly in the orbit and through the lacrimal gland providing parasympathetic and sympathetic innervation to it.

Parasympathetic innervation

nerve of the pterygoid canal]] and then passes through this canal. It emerges in the pterygopalatine fossa and enters the pterygopalatine ganglion where the preganglionic parasympathetic axons synapse with the postganglionic parasympathetic neurons. The postganglionic neurons then send axons which travel with the zygomatic nerve to enter the inferior orbital fissure. As the zygomatic nerve travels anteriorly in the orbit it sends a communicating branch to the lacrimal nerve which carries the postganglionic parasympathetic axons. The lacrimal nerve completes this long pathway by travelling through the lacrimal gland and sending branches to which it provides parasympathetic innervation to increase the secretion of lacrimal fluid.

Sympathetic innervation

Sympathetic innervation to the lacrimal gland is of less physiologic importance than the parasympathetic innervation, however there are noradrenergic axons found within the lacrimal gland. Their cell bodies are located in the superior cervical ganglion.

Clinical significance

In contrast to the normal moisture of the eyes or even crying, there can be persistent dryness, scratching, itchiness and burning in the eyes, which are signs of dry eye syndrome (DES) or keratoconjunctivitis sicca (KCS). With this syndrome, the lacrimal glands produce less lacrimal fluid, which mainly occurs with aging or certain medications. The Schirmer test, conducted by placing a thin strip of filter paper at the edge of the eye, can be used to determine the level of dryness of the eye. Many medications or diseases that cause dry eye syndrome can also cause hyposalivation with xerostomia. Treatment varies according to aetiology and includes avoidance of exacerbating factors, tear stimulation and supplementation, increasing tear retention, eyelid cleansing, and treatment of eye inflammation.

In addition, the following can be associated with lacrimal gland pathology:

Dacryoadenitis
Sjögren's syndrome

Additional images

File:Gray514.png|The ophthalmic artery and its branches. File:Gray776.png|Nerves of the orbit. Seen from above. File:Gray841.png|Sympathetic connections of the sphenopalatine and superior cervical ganglia. File:Gray895.png|The tarsal glands, etc., seen from the inner surface of the eyelids. File:Gray897.png|Alveoli of lacrimal gland.

References

(2012). "Evolution's Witness : How Eyes Evolved".
Moore, Keith. (2018). "Clinically oriented anatomy". Wolters Kluwer.
Machiele, R. (November 2018). "Anatomy Head and Neck". StatPearls [Internet].
Machiele, R. (November 2018). "Anatomy, Head and Neck, Eye Lacrimal Gland". StatPearls(Internet).
"eye, human."Encyclopædia Britannica. 2010. [[Encyclopædia Britannica 2010 Ultimate Reference Suite DVD]] 2010
Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 153.

Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

human-eye-anatomy exocrine-system otorhinolaryngology ophthalmology

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