in what structural layer of the skin and by what cells is melanin produced
Melanocyte Melanocytes (/məˈlænəˌsaɪt, -noʊ-/ ( listen) or /ˈmɛlənəˌsaɪt, -noʊ-/[1][2]) are melanin-producing neural-crest derived[3] cells located in the bottom layer (the stratum basale) of the skin's epidermis, the middle layer of the eye (the uvea),[4] the inner ear,[5] meninges,[6] bones,[7] and heart.[8] Melanin is the pigment primarily responsible for skin color. Once synthesised, melanin is contained in a special organelle called a melanosome and moved along arm-like structures called dendrites, so as to reach the keratinocytes.
Stomach In classical anatomy, the human stomach is divided into four sections, beginning at the gastric cardia,[6] each of which has different cells and functions.
Iris (anatomy) The iris consists of two layers: the front pigmented fibrovascular known as a stroma and, beneath the stroma, pigmented epithelial cells.
Epidermis The stratified squamous epithelium is maintained by cell division within the stratum basale. Differentiating cell delaminate from the basement membrane and are displaced outwards through the epidermal layers, undergoing multiple stages of differentiation until, in the stratum corneum, losing their nucleus and fusing to squamous sheets, which are eventually shed from the surface (desquamation). Differentiated keratinocytes secrete keratin proteins which contribute to the formation of an extracellular matrix and is an integral part of the skin barrier function. In normal skin, the rate of keratinocyte production equals the rate of loss,[4] taking about two weeks for a cell to journey from the stratum basale to the top of the stratum granulosum, and an additional four weeks to cross the stratum corneum.[2] The entire epidermis is replaced by new cell growth over a period of about 48 days.[11]