These melanocytes or ¡°melanin factories¡± are located just below a layer of surface skin cells called keratinocytes.
1. Activation Phase (Stage¥°-Stage¥±)
·The melanocyte stimulating hormone (MSH) activates melanin production.
·MSH binds to a hormone receptor on the melanocyte.
·This binding activates the melanocyte to turn on the synthesis of melanin.
In the initial phase (activation) of the pigmentation process, a hormone initiates melanin production within the melanocyte. Other factors such as stress, hormones, and UV damage can also initiate melanin production.
2. Synthesis Phase (Stage¥²)
Three main chemical reactions exist within the synthesis phase:
·Tyrosinase, an enzyme essential to melanin synthesis, functions to convert tyrosine, an amino acid, to another amino acid called DOPA.
·Tyrosinase then converts DOPA into dopaquinone, a secondary chemical.
·Dopaquinone, in a final reaction, is converted into one of two types of melanin: light melanin (phaeo-melanin) or dark melanin (eu-melanin).
All three reactions occur inside the melanosome located within the melanocyte.
Light melanin (phaeo-melanin) is produced when the environment is abundant in certain amino acids. Dark melanin (eu-melanin) is produced in the absence of these amino acids.
In the production phase (synthesis), melanocytes produce melanin inside an even smaller factory called a melanosome. After a series of complex chemical reactions, the melanosomes are full of melanin and ready for delivery.
3. Expression Phase (Stage ¥³)
Expression is the process through which ¡°packaged¡± melanin is brought to the surface of the skin and made visible to the eye.
·Once melanin has been produced and packaged into melanosomes, the melanocyte initiates a delivery process and pushes the melanosomes out to the ends of its numerous dendrite-like arms.
·As melanosomes reach the ends of these dendrite-like arms, they are transferred from the melanocyte to the adjacent layer of keratinocytes.
·These melanin-filled keratinocytes then make their way to the surface of the skin and melanin becomes visible.
In a final distribution phase (expression), melanosomes are transported to the keratinocytes and to the surface of the skin where the melanin is visible to the naked eye.
|