Melanocytes

Under the Melanocytes Medicine understands the pigment-producing cells in the basal cell layer of the skin. They synthesize melanins, which give skin and hair their color. The most well-known disease associated with melanocytes is black skin cancer.

What are melanocytes?

In the embryonic development phase, the melanocytes migrate from the neural crest and thus into the skin as derivatives of the neuroectoderm. This migration occurs during the third month of the fetal. In the basal cell layer, the cells are located on the basement membrane and are connected to the membrane through hemidesmosomes. Each melanocyte has about six keratinocytes, which are loosely connected to one another.

All melanocytes contain multiple mitochondria and are equipped with a Golgi apparatus and a rough endoplasmic reticulum. The cells lie on the actual skin as well as on the oral mucosa, the choroid and the iris. In addition, melanocytes are located in the bulb and in the root sheath of the hair follicle. The density of these cells is around 1,300 per square millimeter of tissue.

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Anatomy & structure

In the embryonic development phase, the melanocytes migrate from the neural crest and thus into the skin as derivatives of the neuroectoderm. This migration occurs during the third month of the fetal. In the basal cell layer, the cells are located on the basement membrane and are connected to the membrane through hemidesmosomes.

Each melanocyte has about six keratinocytes, which are loosely connected to one another. All melanocytes contain multiple mitochondria and are equipped with a Golgi apparatus and a rough endoplasmic reticulum. The cells lie on the actual skin as well as on the oral mucosa, the choroid and the iris. In addition, melanocytes are located in the bulb and in the root sheath of the hair follicle. The density of these cells is around 1,300 per square millimeter of tissue.

Function & tasks

The job of melanocytes is to produce melanins. This process is also known as melanogenesis. The first step in this is to synthesize tyrosinase. This is an enzyme that contains copper. The enzyme is synthesized in the rough endoplasmic reticulum of the melanocytes. The synthesized enzyme is collected in the Golgi apparatus. The synthesized enzymes are released from the device in the form of round bubbles.

The enzyme has so far been inactive. It is only activated on contact with UV light. The vesicles continue to mature and form crystalline inclusions. These inclusions turn the vesicles into premelanosomes. The amino acid tyrosine migrates into the premelanosomes, which converts the interior into a precursor of melanin as part of a tyron kinase. With the help of the protein Trp-1, the conversion is completed and the premelanosome becomes a mature melanosome. These cells immigrate into the cytoplasmic extensions of the melanocytes and from here are given off to the five to eighth surrounding keratinocytes.

The keratinocytes take up the mature melanosome and store it in their cytoplasm. The UV radiation plays a major role in this process.The fact that human skin is tanned under the sun is due to the increased activity of melanocytes due to UV radiation. Like UV radiation, the hormone melanotropin also stimulates the melanocytes and tans the skin. The melanocytes thus have a direct connection to solar radiation. In this context, pigments have a protective effect. For example, darker skin tones lower the risk of skin cancer. Fair-skinned people are generally more sensitive to UV radiation and more likely to develop black skin cancer.

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Diseases

Hypopigmentation is a below-average coloration of the skin and is usually due to either a low number of melanocytes or a decreased melanin synthesis. In vitiligo, for example, there is patchy hypopigmentation of the skin. The melanocytes are simply missing on the pigmentless areas of the skin. A more well-known phenomenon associated with hypopigmentation is albinism. This is a congenital disorder in the biosynthesis of melanins, which is associated with an unusually light skin and hair color.

Hyperpigmentation of the skin can also occur in the context of various diseases. For example, Addison's disease produces too much melanotropin. This overproduction of the stimulating hormone leads to increased activity of the melanocytes and thus to a dark skin color. Even better known hyperpigmentation occurs in the context of birthmarks. For example, nevus cell nevi are clearly delineated patches of nevus cells. The nevus cells are similar to the melanocytes and can form pigments just like them. Due to the lack of dendrites, however, they cannot release the pigment they produce to the surrounding skin cells.

Dysplastic birthmarks are associated with a certain risk of degeneration and can develop into malignant melanoma. Melanomas can occur on the conjunctiva, on the choroid membrane, on the skin, in the mucous membranes, in internal organs or in the central nervous system. This cancer corresponds to black skin cancer and is an extremely malignant tumor of the melanocytes. Melanomas spread metastases via the lymphatic system or bloodstream at an early stage. Dysplastic birthmarks are therefore removed as early as possible to prevent degeneration. Regular birthmarks, on the other hand, are not considered a threat.