List of abbreviations

Vocabulary of micros- copic anatomy specialist terms explained in English + German

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite Editor: Dr. med. H. Jastrow

Conditions of use

pigment epithelium of the iris (monkey)	melanocyte with a long process human skin	detail therof basal process	melanosom 1 human skin	melanosom 2 human skin	phagocyted melanosomes in a keratinocyte from human skin

melanosomes 1 human melanocyte	melanosomes 2 human melanocyte	pigment epithelium + rod outer segments (monkey)	cells of the pigment epithelium behind retina Bruch'smembrane + choroidea (monkey)	detail on the left (monkey)	detail on the right (monkey)

There are different cells that synthesise pigments and there are also different kinds of pigments. However, most well known are melanocytes of the skin with their pigment melanin.
Melanocytes (Terminologia histologica: Melanocyti) show intensely branched processes which are free of desmosomes and reach from the Stratum basale to the middle of Stratum spinosum (spinous cell layer) of the skin. By means of the UV-ray induceable enzyme tyrosinase melanocytes produce brown-black eumelanin and/or yellow to red phaeomelanins in their cytoplasm. A mixture of these pigments is synthesised in the RER passes the Golgi-apparatus and gets included into vesicles. The latter are called melanosomes (Terminologia histologica: Melanosomae) and further concentrate pigments in 4 stages while they get darker and darker. The melanin containing vesicles (no granules since the are bordered by a membrane) have dimensions of ~100 x 300 nm when cut. They are extruded in toto (i.e. with their membranes) by the melanocytes and incorporated by neighbouring keratinocytes (epithelial cells of the skin) via phagocytosis which then results in melanin-containing heterophagolysosomes.
While maturing melanosomes pass the following stages:
1. premelanosome (stage 1 melanosome; Terminologia histologica: Status 1 Melanosomae, Premelanosomae) have diameters about 100 x 300 nm and are slightly electron-dense since they derive from several fused lysosomes that originated in the Golgi-apparatus. As soon as the homogeneity of the matrix of premelanosomes shows first condensation the latter become
2. stage 2 melanosome vesicles (which erroneously often are called premelanosomes; Terminologia histologica: Status 2 Melanosomae, Vesiculae striatae). The interior of these special lysosomes shows one or several more electron-dense areas with ribbon-like aggregated electron-dense granules. The melanin proper, however, still is NOT formed since the tyrosinase still is inactive.
3. stage 3 melanosomes (Terminologia histologica: status 3 Melanosomae) have an active tyrosinase and thus now show melanin which gets attached to matrix filaments. The number of these granules increases and the areas filled with them grow while the organelles become
4. stage 4 melanosomes (Terminologia histologica: status 4 Melanosomae) are mature melanosomes. Sine the matrix here is full of melanin the activity of the tyrosinase gets more and more reduced. The interior of the mature melanosome is extremely electron-dense.
The number of melanosomes per keratinocyteis genetically determined. The paler the skin, the lower their amount. In Europeans the number varies between 16 – 132 while in people originating from countries near the equator it is between 80 – 160.

An English page with more detailed information and further images is only available in the professional version of this atlas.

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