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The Melanocyte
Melanocyte Structure and Function
| Question | Answer |
|---|---|
| Where are melanocytes located in the epidermis? | basal layer |
| What is the ratio of melanocytes to keratinocytes? | 1:10 |
| What is the epidermal melanin unit? | approx 36 keratinocytes in contact with 1 melanocyte |
| What factors stimulate melanocytes? | FGF-beta, TGF-beta |
| What factors inhibit melanocytes? | IL-1, IL-6, TGF-beta |
| What does tyrosinase require as a cofactor? | copper |
| What are the steps in melanin synthesis? | Tyrosine - DOPA - Dopaquinone - Pheomelanin/Eumelanin |
| What enzyme is required to convert tyrosine to DOPA and DOPA to Dopaquinone? | Tyrosinase |
| Which form of melanin is brown/black in color? | Eumelanin |
| Which form of melanin is red/yellow in color? | Pheomelanin |
| What is the function of P protein? | involved in tyrosine transfer |
| P protein is defective in what disorder? | OCA2 |
| What is the precursor protein to MSH (melanocyte-stimulating hormone)? | POMC |
| POMC forms which two hormones? | ACTH and MSH |
| What is the receptor to which MSH binds on the melanocyte? | MC1R (melanocortin 1 receptor) |
| What is the result of loss of function mutation in MC1R? | pheomelanin production and red hair/fair skin |
| What is the spectrum of UV light? | 280-400nm |
| What are the shape of pheomelanin melanosomes? | spheroid/circular with microvesicular internal structure |
| What are the shape of eumelanin melanosomes? | elliptical/oval with lamellar internal structure |
| What are the 4 stages of melanosomes? | 1) spherical 2) episoidal 3) matrix is melanized 4) melanization is complete |
| What cell organelle is the melanosome related to? | lysosome |
| Binding of MSCH to MC1R generates what intracellular response? | G protein activation and increase cAMP |
| What is apocapation? | name for the process of transfer of melanosomes via phagocytosis of the dendritic tips of the melanocytes by the keratinocytes |
| In what part of the epidermis is melanin preferentially distributed? | basal layer |
| What is the gene defect in OCA1? | Tyrosinase |
| What is the gene defect in OCA2? | P protein |
| How are melanosomes different in people with darker skin? | -greater production of melanosomes -larger melanosomes -higher degree of melanization -higher degree of dispersion of the melanosomes -slower rate of degradation -melanosomes are transferred as individual organelles |
| What is the difference in melanosome transfer between patients with light and dark skin? | in light skin, melanosomes transferred as membrane-bound clusters -in dark skin, melanosomes transferred as individual organelles |
| What is a melanin unit composed of? | One melanocyte to five keratinocytes |
| Where in the hair follicle does the melanin unit exist? | proximal anagen bulb |
| What is the MOA of hydroquinone? | inhibits tyrosinase |
| Why does hair graying occur? | gradual decline in the number of follicular melanocytes |
Created by:
criddel