Lacrymal secretion

The comeal epithelium is made of stratified and keratinless scale-like and junction-like cells. These cells are arranged on 4-6 layers at the central part and 4-8 layers on the edge of the cornea. Their combined thickness is about 50-60 pm representing about 10% of the whole thickness of the cornea. The structure and function of the epithelium strictly depends on the lacrymal secretion that covers it and plays a big part in the preservation of the cells and in their transparency. 

We will now study, from edge to center, the lacrymal secretion and the layers of the comeal epithelium. 

It cannot be dissociated from the epithehum because they share optic and metabolic functions. The lacrymal secretion is made up of three layers, from outside to inside ... 

A deep layer rich in mucus and the origin of which is to be found in the conjunctival calyciform cells. This mucus is in relation with the apical epithelial cells via the glycocalyx. This interface between the lacrymal secretion and the epithelium influences the quality of the corneal surface. Indeed, the stability of the lacrymal secretion and the epithelial absorption of its metabolites both depend on the mucin and the apical expansions of the epithelial cells [2]. 

Thanks to specular microscopy and electron scanning microscopy, some cells with various aspects have been identified it could be different stages of differentiation and maturation of the superficial cells preceding their desquamation. Along their evolution, the metabolic activity of the superficial cells slows down until it stops. They are then evacuated into the lacrymal secretion. 

Their cytoplasmic membrane is bristled up with microvillosities and micropilis. They increase the exchange surface with the lacrymal secretion and enable its fixing. Their lateral and basal cytoplasmic membranes have got junctional complexes uniting these superficial cells together. There are three types of junctional complexes ... 

AO. 1 ptm thick superficial lipidic layer with a main function of reducing the speed of evaporation of the lacrymal secretion. This lipidic film can only be... 

The Harderian gland, wrapped behind the eyeball, is especially prominent in rodents. It produces a variable, primarily lipid secretion and drains through the Harderian-lacrymal tract and the external nares. In Mongolian gerbils, the secretion is spread over the body during grooming (Thiessen ct ah, 1976). A pheromonal function has not been clearly established. 

A middle 7-pm thick aqueous layer secreted by the lacrymal glands, with an average debit of... 

Inner layer, a mucus layer secreted by the conjuc-tiva goblet cells and the lacrymal gland. This layer is important for wetting the corneal and conjuctival epithelia. 

By naufea. 7. By averfico- %. By catenation voith Jlimulating fubfiances in the ear. II. i. Secretion of tears lefs in fleep., Brom fiimulation of their excretory duct. 2. Lacrymal fack is a... 

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