Skin is the largest organ in the human body, thus resulting in it having millions of cells that die and divide every day and even every second. In this section I will discuss the upper layers of skin, how skin is formed and melanin production and function. The cutis (scientific name for skin) is divided into three sub layers that all have different cellular reactions happening constantly. The three layers of cutis are epidermis, dermis and subcutaneous layer. Skin is the frontline of your body preventing any liquids or foreign objects entering your body.
The three layers of skin mentioned above contain cells that all do different jobs resulting in one functioning organ. The topmost layer of skin is the epidermis. This is where millions of cells are shed of daily. The rate that skin cells (keratinocytes) die and are shed off is about 30-40 thousand cells per minute in a fully-grown adult. The epidermis consists of two dominant types of cells keratinocytes and melanocytes. About 95% of skin consists of keratinocytes that divide in the basal layer (Stratum Basale). The epidermis is divided into five different layers biggest being the basal layer. The basal layer is the site of the formation keratinocytes.
Keratinocytes arise from epidermal stem cells that are situated at the bottom of the epidermal layer. When new keratinocytes are formed they withdraw the cell cycle and thus start their way moving up to the stratum corneum. When the cell passes through different layers of the epidermis it loses contact to blood vessels that used to provide energy to the formation of the cell. In result of the differentiation process the keratinocyte becomes flatter, shedding its nucleus and cytoplasm.
The process of the keratinocytes flattening and loss of nucleus and cytoplasm results in the keratinocyte becoming an ceratinocyte. When the ceratinocyte has reached the stratum corneum the cell flattens and is shed off. The epidermis, more specifically the Stratum Basale contains another type of cell that produces melanin. Melanin pigmentation defines your skin tone since the color of the pigment varies according to many factors that I will discuss later. Melanocytes are the cells that produce melanin.
Every human being has almost the same number of Melanocytes, but skin color is affected by factors such as DNA, UV exposure and diseases. Melanin production starts by the melanocyte analyzing your DNA and produce enzymes which act like catalyst that boost chemical reactions. The melanocyte also produces tyrosine acordingly to your DNA, it is an amino acid that is used to convert to melanin. The tyrosine is transported into melanosomes (organelle) where it is converted into melanin. When the tyrosine is converted into melanin it is then transported out by the melanocyte into the basal layer where the melanin then makes its way to the top. Melanin related diseases are rare but possible.
One of the diseases is albinism, it is when a mutated gene restricts production of melanin. Melanin is an essential pigment that shields our skin from dangerous UV-B rays.