Dr. Mohammad Akkawe. The lacrimal glands are paired almond- shaped glands, one for each eye, that...

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Transcript of Dr. Mohammad Akkawe. The lacrimal glands are paired almond- shaped glands, one for each eye, that...

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  • Dr. Mohammad Akkawe
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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.
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  • 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.
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  • The lacrimal gland is tubuloacinar gland derived from surface ectoderm with ducts lined by a low columnar or cuboidal epithelium (often bilayered). The secretory cells in the acini have a predominance of dense granules, suggesting that most are of a serous nature However, some cells are mucus producing
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  • The lobules of the orbital portion of the lacrimal gland are near the orbital septum but lie under the levator muscle. The fornix of the upper eyelid lies immediately adjacent to the accessory lacrimal gland of Krause
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  • The glands of Krause are accessory lacrimal glands having the same structure as the main gland. They are placed deeply in the subconjunctival connective tissue (mainly) of the upper fornix between the tarsus and the inferior lacrimal gland, of which they are offshoots. There are some 42 in the upper and 6 to 8 in the lower fornix.
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  • Glands of Wolfring are also accessory lacrimal glands, but larger than the glands of Krause. There are 2 to 5 in the upper lid situated actually in the upper border of the tarsus about its middle between the extremities of the tarsal glands or just above the tarsus.
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  • The postganglionic secretomotor fibres (which arise from the pterygopalatine ganglion) hitch-hike on the zygomaticotemporal and lacrimal nerves to the gland
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  • The accessory lacrimal tissue found at various sites in the conjunctiva is histologically identical to the main lacrimal gland, as are the secretions it produces
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  • Tear secretion can be classified as basal secretion and reflex secretion the concept of basal tear production is a redundant one, as even minimal tear production in the undisturbed eye is thought to be secondary to light or temperature stimulation or both
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  • Reflex tearing is mediated via parasympathetic nerves that stimulate the myoepithelial cells lining lacrimal acini, causing them to contract These fibers originate in the superior salivatory nucleus and lesions in this region will reduce reflex tearing Sympathetic nerves may influence tear production by altering the blood flow to the lacrimal glands
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  • The underlying mechanism of psychogenic tearing is not clearly understood, but it is always bilateral
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  • The original model of the precorneal tear film described a trilayered film composed of: anterior lipid layer, middle aqueous layer an inner hydrophilic mucin layer produced by the goblet cells
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  • lipidAqueousMucoid [email protected] the corneal epithelium Thickness 0.1 m10 m30 m Secreted byMeibomian glands, glands of Zeis Lacremal glands, accessory lacremal gland Conjunctiva Function Reduces evaporation. Prevents overflow from lid margin Contains nutrients. Uptakes O2 from cornea Allows the tear film to spread evenly on a hydrophopic corneal surface
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  • Until recently it was thought that the mucin layer is