Lacrimal gland

The lacrimal glands are paired 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.

Anatomy
Each lacrimal gland is divided into orbital and palpebral portions by the aponeurosis of the Levator palpebrae superioris muscle, the portions are continuous with each other.


 * The orbital portion is the largest of the portions, and its convex superior surface is lodged in the lacrimal fossa of the orbit.
 * For the smaller palpebral portion, its inferior surface lies close to the eye; 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.

Structure
The lacrimal gland is a tubuloacinar gland, it is made up of many lobules separated by connective tissue, each lobule contains many acini.

Each acinus consists of a grape-like mass of cells with their apices pointed to a central lumen.

The central lumen of many of the units united to form intralobular ducts, and then unite to from interlobular ducts.

Innervation
The sensory innervation to the lacrimal gland is from the lacrimal nerve of the trigeminal nerve.

The parasympathetic nerve supply originates from the lacrimal nucleus of the facial nerve in the pons. Just before reaching the geniculate ganglion, the facial nerve gives off the greater petrosal nerve. This nerve carries the parasympathetic secretomotor fibers through the pterygoid canal to the pterygopalatine ganglion. Here the fibers synapse and postganglionic fibers join the inferior orbital nerve, which travels through the inferior orbital fissure. Once it has traversed this opening, the parasympathetic secretomotor fibers join a branch of this inferior orbital nerve, namely the zygomatic nerve, part of which innervates the lacrimal gland.

The sympathetic postganglionic fibres originates from the superior cervical ganglion. They travel as a periarteriolar plexus with the middle meningeal 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. However they join the parasympathetic fibers, hence from this point on the routes of the parasympathetic and sympathetic fibers for the lacrimal gland are the same (inferior orbital nerve -> inferior orbital fissure -> zygomatic nerve -> lacrimal gland).

Blood supply
The lacrimal artery, derived from the ophthalmic artery supplies the lacrimal gland. Venous blood returns via the superior ophthalmic vein.

Pathology

 * Dacryoadenitis
 * Sjögren's syndrome