lacrimal gland

Thelacrimal glandsare paired almond-shaped glands, one for each eye, that secrete the aqueous layer of the tearfilm. They are situated in the upper, outer portion of each orbit, in the lacrimal fossaof 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 ductinto the nose. Anatomists divide the gland into two sections. The smallerpalpebral portionlies close to the eye, along the inner surface of the eyelid; if the upper eyelidis everted, the palpebral portion can be seen. The orbital portion contains fine interlobular ductsthat 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 canaliculion to the lacrimal sac, in turn to the nasolacrimal duct, which dumps them out into the nose. [ 2 ] Microanatomy The lacrimal gland is a compound tubuloacinar gland, it is made up of many lobulesseparated 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 oflacrimal gland cellswith 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 parasympatheticnerve supplyoriginates from the lacrimal nucleusof the facial nervein the pons. Just distal to the geniculate ganglion, the facial nerve gives off the greater petrosal nerve. This nerve carries the parasympathetic secretomotor fibers through the pterygoid canal, 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, which travels through the inferior orbital fissure. Once it has traversed this opening, the parasympathetic secretomotor fibers branch off with the zygomatic nerveand 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 sympatheticpostganglionic fibersoriginate 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 nervein 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 arterysupplies the lacrimal gland. Venous blood returns via the superior ophthalmic vein.