| Melanin |
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MELANIN IN HUMANS In humans, melanin is found in Skin , Hair , the pigmented tissue underlying the Iris , the Medulla and Zona Reticularis of the Adrenal Gland , the Stria Vascularis of the Inner Ear , and in pigment bearing neurons of certain deep brain nuclei such as the Locus Ceruleus and the Substantia Nigra . Melanin is the primary determinant of Human Skin Color . Dermal melanin is produced by Melanocyte s, which are found in the Stratum Basale of the Epidermis . Although human beings generally possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups more frequently or less frequently Express the melanin-producing Gene s, thereby conferring a greater or lesser concentration of skin melanin. Some individual animals and humans have very little or no melanin in their bodies, a condition known as Albinism . Because melanin is an aggregate of smaller component molecules, there are a number of different types of melanin with differing proportions and bonding patterns of these component molecules. Both pheomelanin and eumelanin are found in human skin and Hair , but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in Albinism . Eumelanin Polymer s have long been thought to comprise numerous cross-linked 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) polymers; recent research into the electrical properties of eumelanin, however, has indicated that it may consist of more basic Oligomer s adhering to one another by some other mechanism. Thus, the precise nature of eumelanin's molecular structure is once again the object of study. Eumelanin is found in hair and skin, and colors hair grey, black, yellow, and brown. In humans, it is more abundant in peoples with dark skin. There are two different types of eumelanin, which are distinguished from each other by their pattern of polymer bonds. The two types are black eumelanin and brown eumelanin. Black eumelanin is the darkest, brown eumelanin is lighter than black eumelanin. black eumelanin is in mostly non-Europeans and aged Europeans, while brown eumelanin is in mostly young Europeans. A small amount of black eumelanin in the absence of other pigments causes grey hair. A small amount of brown eumelanin in the absence of other pigments causes yellow (blond) color hair. Pheomelanin is also found in hair and skin and is both in lighter skinned humans and darker skinned humans. But women have more pheomelanin than men hence women's skin is more reddishness than men's. Pheomelanin imparts a pink to red hue and, thus, is found in particularly large quantities in red hair. Pheomelanin is particularly concentrated in the lips, nipples, glans of the penis, and vagina. Pheomelanin also may become Carcinogenic when exposed to the ultraviolet rays of the sun. Chemically, pheomelanin differs from eumelanin in that its oligomer structure incorporates the amino acid L-cysteine, as well as DHI and DHICA units. Neuromelanin is the dark pigment present in pigment bearing neurons of four deep brain nuclei: the Substantia Nigra (in Latin , literally "black substance") - Pars Compacta part, the Locus Ceruleus ("blue spot"), the dorsal motor nucleus of the Vagus Nerve (cranial nerve X), and the median Raphe Nucleus of the Pons . Both the Substantia Nigra and Locus Ceruleus can be easily identified grossly at the time of autopsy due to their dark pigmentation. In Humans , these nuclei are not pigmented at the time of birth, but develop pigmentation during maturation to adulthood. Although the functional nature of neuromelanin is unknown in the brain, it may be a byproduct of the synthesis of Monoamine Neurotransmitters for which the pigmented Neurons are the only source. The loss of pigmented Neurons from specific nuclei is seen in a variety of Neurodegenerative Disease s. In Parkinson's Disease there is massive loss of Dopamine producing pigmented neurons in the Substantia Nigra . A common finding in advanced Alzheimer's Disease is almost complete loss of the Norepinephrine producing pigmented neurons of the Locus Ceruleus . Neuromelanin has been detected in Primate s and in Carnivore s such as Cat s and Dog s. MELANIN IN OTHER ORGANISMS |
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