retinal pigment epithelium

epithelium

pl. epithelia [Gr.] the cellular covering of internal and external surfaces of the body, including the lining of vessels and other small cavities. It consists of cells joined by small amounts of cementing substances. Epithelium is classified into types on the basis of the number of layers deep and the shape of the superficial cells. Standard classifications include ciliated (cilia attached), columnar (taller than wide), cuboidal (same height as width), pseudostratified (single layer but because of varying cell height appears to be more than one), simple (one cell layer), squamous (flattened, plate-like cells), stratified (more than one layer), transitional (variable number of layers apparent). Other types are listed below.

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anterior epithelium

the thin layer of stratified squamous cells that form the outermost layer of the cornea.

corneal epithelium

see anterior epithelium (above).

germinal epithelium

thickened peritoneal epithelium covering the gonad from earliest development; formerly thought to give rise to germ cells.

glandular epithelium

that composed of secreting cells.

lens epithelium

cuboidal epithelium covering the lens.

pigmentary epithelium, pigmented epithelium

that made of cells containing granules of pigment.

posterior epithelium

the single layer of epithelial cells on the back of the cornea, between stroma and aqueous humour; the corneal endothelium.

retinal pigment epithelium

see retina.

sense epithelium, sensory epithelium

see neuroepithelium (1).

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retinal pigment epithelium (RPE) 

A brown monolayer of cells of the retina situated next to the choroid composed of cells joined by tight junctions and filled with pigment, mainly melanin and lipofuscin (Fig. R9). Depending upon the amount of pigment, the fundus will appear dark or light. The main functions of the RPE are: control of the flow of fluid and nutrients entering the retina (blood-retina barrier), absorption of scattered light, visual pigment metabolism, vitamin A metabolism which contributes to visual pigment regeneration, ingestion and digestion of photoreceptor discs (phagocytosis), retinal adhesion and synthesis of growth factors of adjacent tissues. A dysfunction of this tissue can be detected with the electrooculogram. See Bruch's membrane; Usher's syndrome.

Fig. R9  Schematic representation of the cells and layers of the central primate retina (1: retinal pigment epithelium; 2: layer of rods and cones; 3: external limiting membrane; 4: outer nuclear layer; 5: outer plexiform layer; 6: inner nuclear layer; 7: inner plexiform layer; 8: ganglion cell layer; 9: nerve fibre layer; 10: internal limiting membrane)