The lacrimal glands are paired , one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tears 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 orbital lobe of the gland, contains fine interlobular ducts that connect the orbital lobe and the palpebral lobe.["eye, human."Encyclopædia Britannica. 2010. Encyclopædia Britannica 2010 Ultimate Reference Suite DVD 2010]
Lacrimal glands are also present in other , 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
Acinus. 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
parasympathetic innervation to the lacrimal gland is a complex pathway which traverses through numerous structures in the head. Ultimately this two-neuron pathway involving both a preganglionic and postganglionic parasympathetic neuron increases the secretion of lacrimal fluid from the lacrimal gland. The preganglionic parasympathetic neurons are located in the superior salivatory nucleus. They project axons which exit the brainstem as part of the
facial nerve (CN VII). Within the
facial canal at the geniculate ganglion the axons branch from the facial nerve forming the greater petrosal nerve. This nerve exits the facial canal through the hiatus for the greater petrosal nerve in the petrous part of the temporal bone. It emerges to the middle cranial fossa and travels anteromedially to enter the
foramen lacerum. Within the foramen lacerum it joins to the deep petrosal nerve to form the 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.
[Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 153.]
In addition, the following can be associated with lacrimal gland pathology:
Additional images
See also
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Lacrimal apparatus
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Preorbital gland
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Accessory lacrimal glands
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List of distinct cell types in the adult human body
External links
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()
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Diseases of the lacrimal gland at http://www.academy.org.uk/lectures/barnard11.htm
