Lacrimal gland

Tear organs are part of the accessory apparatus of the eye, which protects the eyes from external influences and protects the conjunctiva and the cornea from drying out. Lacrimal organs produce and divert tear fluid into the nasal cavity; they consist of a lacrimal gland, additional small lacrimal glands and tear ducts. The lacrimal fluid produced by the lacrimal glands is of great importance for the normal function of the eye, since it moisturizes the cornea and conjunctiva. The ideal smoothness and transparency of the cornea, the correct refraction of the light rays at its anterior surface are due to, among other factors, the presence of a thin layer of tear fluid covering the anterior surface of the cornea. Lacrimal fluid also helps purify the conjunctival cavity from microorganisms and foreign bodies, prevent the drying of the surface, and ensure its nutrition.

The orbital part of the lacrimal gland is laid in the embryo at the age of 8 weeks. By the time of birth tear fluid is almost not released, as the lacrimal gland is not yet developed enough. In 90% of children, only the second month of life begins active tearing. The teardrop device is formed from the 6th week of embryonic life. From the orbital angle of the nasolacrimal groove in the connective tissue, the epithelial cord is sinking, which is gradually loosened from the original epithelial cover of the face. By the 10th week this line reaches the epithelium of the inferior nasal passage and at the 11th week it turns into a channel lined with epithelium, which at first terminates blindly and opens at 5 months to the nasal cavity. About 35% of children are born with a membrane closed by the outlet of the nasolacrimal influx. If in the first weeks of a child's life this membrane does not resolve, dacryocystitis of the newborns may develop, requiring manipulation to create patency of the tear along the canal to the nose.

The lacrimal gland consists of 2 parts: the upper part, or the orbital (orbital) part and the lower, or the secular (palpebral) part. They are separated by a wide tendon of the muscle that lifts the upper eyelid. The glaucous part of the lacrimal gland is located in the fossa of the lacrimal gland of the frontal bone on the lateral-upper wall of the orbit. Sagittal size is 10-12 mm, frontal - 20-25 mm, thickness - 5 mm. Normally, the orbital part of the gland is inaccessible to external examination. It has 3-5 excretory canals, passing between the lobes of the secular part, opening in the upper arch of the conjunctiva from the side 4-5 mm from the upper edge of the tarsal plate of the upper cartilage of the eyelid. The secular part of the lacrimal gland is much smaller than the ophthalmic gland, located beneath it under the upper arch of the conjunctiva from the temporal side. The size of the secular part is 9-11 x 7-8 mm, the thickness is 1-2 mm. A number of excretory canals of this part of the lacrimal gland discharge into the excretory canals of the orbital part, and the 3-9 canals open independently. Multiple excretory canals of the lacrimal gland create a kind of a kind of "soul", from the holes of which the tear enters the conjunctival cavity.

The lacrimal gland belongs to the complex tubular serous glands; its structure is similar to the parotid gland. The terminal tubules of greater caliber are lined with a two-layered cylindrical epithelium, and of a smaller caliber, by a single-layered cubic epithelium. In addition to the main lacrimal gland, there are small additional tubular lacrimal glands: in the arch of the conjunctiva are the conjunctival glands of Krause and at the upper edge of the cartilage of the eyelids, in the orbital part of the conjunctiva are the glands of Valdeier. In the upper arch of the conjunctiva, there are 8-30 additional glands, in the lower - 2-4. The ligament gland is retained by its own ligaments that attach to the periosteum of the upper wall of the orbit. The ligament is also strengthened by Lockwood's ligament, suspending the eyeball, and the muscle lifting the upper eyelid. The lacrimal gland is supplied with blood from the tear duct - the branch of the orbital artery. Outflow of blood occurs through the lacrimal vein. The lacrimal gland is innervated by the branches of the first and second branches of the trigeminal nerve, the branches of the facial nerve and sympathetic fibers from the upper cervical node. The main role in the regulation of the secretion of the lacrimal gland belongs to parasympathetic fibers that are part of the facial nerve. The center of reflex tearing is in the medulla oblongata. In addition, there is a number of vegetative centers, the irritation of which intensifies tearing.

The tear ducts start with a teardrop. This is the capillary gap between the posterior rib of the lower eyelid and the eyeball. A tear streams down the stream to the teary lake, located at the medial node of the eye gap. At the bottom of the lacrimal lake there is a small elevation - a teardrop. The lower and upper lacrimal points are immersed in the lacrimal lake. They are on the tops of the lachrymal papillae and normally have a diameter of 0.25 mm. The lower and upper lacrimal canals start from the dots, which first go up and down respectively 1.5 mm, and then, bending at right angles, go to the nose and flow into the lacrimal sac, more often (up to 65%) in the common mouth. On the place of their confluence in the bag, a sinus is formed on top - the sine of Mayer; there are folds of the mucosa: from below - the valve Gushke, from above - the valve of Rosenmuller. The length of the lacrimal tubules is 6-10 mm, the lumen is 0.6 mm.

The lacrimal sac is located behind the inner ligament of the eyelids in the tear fovea formed by the frontal process of the upper jaw and the tear bone. Surrounded by loose fiber and a fascial case, a sack rises 1/3 above the inner ligament of the eyelids with its arch, and below it passes into the nasolacrimal duct. The length of the lacrimal sac is 10-12 mm, the width is 2-3 mm. The walls of the bag consist of elastic and interwoven muscle fibers of the age-old part of the circular muscle of the eye - Gorner's muscle, the contraction of which contributes to the suction of tears.

Nasolacrimal duct, the upper part of which is enclosed in the bony nasolacrimal canal, passes in the lateral wall of the nose. The mucous membrane of the lacrimal sac and the nasolacrimal duct is tender, has the character of an adenoid tissue, is lined with a cylindrical, sometimes ciliated epithelium. In the lower sections of the nasolacrimal duct, the mucous membrane is surrounded by a dense venous network like a cavernous tissue. Nasolacrimal duct is longer than the bone nasolacrimal canal. At the exit to the nose there is a fold of the mucous membrane - the tear valve of Gasner. A nasolacrimal duct opens under the anterior end of the inferior nasal concha at a distance of 30-35 mm from the entrance to the nasal cavity in the form of a wide or sagged opening. Sometimes the nasolacrimal duct passes in the form of a narrow tubule in the nasal mucosa and opens away from the opening of the bone nasolacrimal canal. The last two variants of the structure of the nasolacrimal duct can cause rhinogenic disorders of tearing. The length of the nasolacrimal duct is from 10 to 24 mm, width is 3-4 mm.

[1], [2], [3], [4], [5], [6], [7], [8],

The lacrimal apparatus of the eye

The lacrimal apparatus (lacrimalis) includes a lacrimal gland with its excretory canals opening into the conjunctival sac, and the tear ducts. The lacrimal gland (glandula lacrimalis) is a complex alveolar-tubular gland of the lobate structure, lies in the epithelial pit in the lateral corner, in the upper wall of the orbit. The tendon of the muscle that lifts the upper eyelid divides the gland into a large upper orbital part (pars orbitalis) and a smaller lower secular part (pars palpebralis) lying near the upper arch of the conjunctiva.

Under the arch of the conjunctiva, sometimes additional tear glands (glandulae lacrimales accessoriae) are of small size. The outflow canals (ductuli excretorii) of the lacrimal gland in an amount of up to 15 open into the conjunctival sac in the lateral part of the superior arch of the conjunctiva. Exiting the tubules, a tear (tear fluid) washes the anterior part of the eyeball. Next, a tear fluid along the capillary gap near the edges of the eyelids along the lacrimal stream (rivus lacrimals) flows into the medial corner of the eye, into the lacrimal lake. In this place, short (about 1 cm) and narrow (0.5 mm) curved upper and lower lacrimal canals (sialiculi lacrimales) originate. These tubules open into the lacrimal sac separately or connected to each other. The lacrimal sac (saccus lacrimalis) lies in the eponymous pit in the lower medial corner of the orbit. He goes over to a rather wide (up to 4 mm) nasolacrimal duct (ductus nasolacrimalis) ending in the nasal cavity, in the anterior part of the lower nasal passage. With the front wall of the lacrimal sac, the lacrimal part of the circular muscle of the eye is fused, which, when contracted, expands the lacrimal sac, which contributes to sucking tear fluid into it through the tear ducts.