The skin is the largest organ of the human body. The skin consists of three layers. The top layer is formed by the epidermis. The middle layer is called the dermis. The bottom layer is the subcutaneous connective tissue. The epidermis consists mainly of special skin cells called the keratinocytes. The keratinocytes are formed in the lower layer (the basal layer) and slowly slide upwards from there. Gradually they transfer to a dead keratinized cell layer, the horny layer, where the cells lie loosely against each other.
Melanocytes are present in the epidermis, in addition to the keratinocytes. Melanocytes are pigment cells that lie between the cells of the basal cell layer and make the pigment grains that are transferred via offshoots to the keratinocytes. The pigment of the pigment granules, the melanin, determines to a large extent the color of the skin and protects us from sunlight. The more pigment grains, the darker the skin. Pigment is a brown dye that is produced by the pigment cells in the lower layer of the epidermis. Pigment cells lay therefore relatively superficial in the skin. In the pigment cell, the pigment is packaged in pigment granules, and thus delivered to the upper epidermal cells. Only when the pigment is in the epidermal cells the skin is visibly pigmented.
The functions of pigment cells are besides determining the skin color also protecting the skin against harmful ultraviolet (UV) rays. Under the influence of UV radiation, the number of active pigment cells and pigment production increases. The result is a brown discoloration of the skin.
With thanks to Dr. Eddie Wisse and Frank van Campen, members of the Royal Antwerp Society for Micrography.
Prepared slide by Lieder www.lieder.com
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