Lacrimal gland
| Lacrimal gland | |
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Lacrimal apparatus of the right eye. The lacrimal gland is to the upper left. The right side of the picture is towards the nose.
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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 |
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| Details | |
| Latin | glandula lacrimalis |
| lacrimal artery | |
| lacrimal nerve, Zygomatic nerve via Communicating branch, greater petrosal nerve | |
| Identifiers | |
| Dorlands /Elsevier |
g_06/12392431 |
| TA | Lua error in Module:Wikidata at line 744: attempt to index field 'wikibase' (a nil value). |
| TH | {{#property:P1694}} |
| TE | {{#property:P1693}} |
| FMA | {{#property:P1402}} |
| Anatomical terminology
[[[d:Lua error in Module:Wikidata at line 863: attempt to index field 'wikibase' (a nil value).|edit on Wikidata]]]
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The lacrimal glands are paired almond-shaped glands, one for each eye, that secrete the aqueous layer of the tear film. They are situated in the upper, outer portion of each orbit, in the lacrimal fossa of the orbit formed by the frontal bone.[1] Inflammation of the lacrimal glands is called dacryoadenitis. The lacrimal gland produces tears which then flow into canals that lead to the lacrimal sac. From this sac, the tears drain through the lacrimal duct into the nose.
Anatomists divide the gland into two sections. The smaller palpebral portion 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 portion contains fine interlobular ducts that unite to form 3–5 main excretory ducts, joining 5–7 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.[2]
Contents
Microanatomy
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 contain only serous cells and produce a watery serous secretion.
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 unite to from interlobular ducts. The gland lacks striated ducts.
Innervation
The parasympathetic nerve supply originates from the lacrimatory nucleus of the facial nerve in the pons. From this nucleus preganglionic parasympathetic fibres run in the nervus intermedius (small sensory root of facial nerve) to the geniculate ganglion but do not synapse here. Then from the geniculate ganglion, the preganglionic fibres run in the greater petrosal nerve, a branch of the facial nerve. This nerve carries the parasympathetic secretomotor fibers through the foramen lacerum, where it joins the deep petrosal nerve (containing postganglionic sympathetic fibers from the superior cervical ganglion) to form the nerve of the pterygoid canal (vidian nerve). This nerve travels through the pterygoid canal to the pterygopalatine ganglion. Here the fibers synapse and postganglionic fibers join the fibers of the maxillary nerve. In the pterygopalatine fossa itself, the parasympathetic secretomotor fibers branch off with the zygomatic nerve and then branch off again, joining with the lacrimal branch of the ophthalmic division of CN V, which supplies sensory innervation to the lacrimal gland along with the eyelid and conjunctiva.
The sympathetic postganglionic fibers originate from the superior cervical ganglion. They travel as a periarteriolar plexus with the internal carotid artery, before they merge and form the deep petrosal nerve, which joins the greater petrosal nerve in the pterygoid canal. Together, greater petrosal and deep petrosal nerves form the nerve of the pterygoid canal (vidian nerve) and reach the pterygopalatine ganglion in the pterygopalatine fossa. In contrast to their parasympathetic counterparts, sympathetic fibers do not synapse in the pterygopalatine ganglion, having done so already in the sympathetic trunk. However, they continue to course with the parasympathetic fibers innervating the lacrimal gland.
Blood supply
The lacrimal artery, derived from the ophthalmic artery supplies the lacrimal gland. Venous blood returns via the superior ophthalmic vein.
Lymphatic drainage
The glands drain into the superficial parotid lymph nodes.[3]
Nerve supply
The lacrimal nerve, derived from the ophthalmic nerve, supplies the sensory component of the lacrimal gland. The greater petrosal nerve, derived from the facial nerve, supplies the parasympathetic autonomic component of the lacrimal gland. The greater petrosal nerve travels alongside branches of the V1 and V2 divisions of the trigeminal nerve. This proximity of the greater petrosal nerve to branches of the trigeminal nerve explains the phenomenon of lesions to the trigeminal nerve causing impaired lacrimation although the trigeminal nerve does not supply the lacrimal gland.
Pathology
In contrast to normal moisture of the eyes or even crying, there can be persistent dryness, scratching, 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. A thin strip of filter paper placed at the edge of the eye, the Schirmer test, can 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 etiology and includes avoidance of exacerbating factors, tear stimulation and supplementation, increasing tear retention, eyelid cleansing, and treatment of eye inflammation.[3]
In addition, the following can be associated with lacrimal gland pathology:
Additional images
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The ophthalmic artery and its branches.
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Nerves of the orbit. Seen from above.
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Sympathetic connections of the sphenopalatine and superior cervical ganglia.
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The tarsal glands, etc., seen from the inner surface of the eyelids.
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Alveoli of lacrimal gland.
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Extrinsic eye muscle. Nerves of orbita. Deep dissection.
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Extrinsic eye muscle. Nerves of orbita. Deep dissection.
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Extrinsic eye muscle. Nerves of orbita. Deep dissection.
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Extrinsic eye muscle. Nerves of orbita. Deep dissection.
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Extrinsic eye muscle. Nerves of orbita. Deep dissection.
See also
References
- ↑ Clinically Oriented Anatomy, Moore, Dalley & Agur.
- ↑ "eye, human."Encyclopædia Britannica. 2010. Encyclopædia Britannica 2010 Ultimate Reference Suite DVD 2010
- ↑ 3.0 3.1 Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 153.
External links
- lesson3 at The Anatomy Lesson by Wesley Norman (Georgetown University) (orbit2)
- Diseases of the lacrimal gland at http://www.academy.org.uk/lectures/barnard11.htm
