TY  - CHAP
M1  - Book, Section
TI  - Pigmentary Disorders
A1  - Nezafati, Kaveh A.
A1  - Romero, Roger
A1  - Pandya, Amit G.
A2  - Ali, Asra
PY  - 2015
T2  - McGraw-Hill Education Specialty Board Review Dermatology: A Pictorial Review, 3e
AB  - Epidermal  melanocytes  are  dendritic  cells  derived  from  neural  crest  cellsTheir  migration  and  differentiation  is  influenced  by  a  number  of  signaling  molecules:  steel  factor  (stem  cell  factor,  c-Kit  ligand),  Wnt,  bone  morphogenic  proteins  (BMPs),  and  hepatocytes  growth  factorProvide  melanin  for  36  neighboring  basal  and  spinous  layer  keratinocytes  =  one  epidermal  melanin  unitNumber  and  distribution  are  the  same  in  all  skin  types  and  ethnicitiesConcentration  and  distribution/retention  of  melanosomes  in  keratinocytes  cause  different  skin  colorsTypes  of  melanin:Pheomelanin:  red-yellowEumelanin:  brown-blackMelanosomesMembrane-bound  organelles,  site  of  melanin  synthesis  and  storageFound  in  melanocytes;  they  move  from  melanocytes  to  keratinocytesTypes  of  melanosomes:Eumelanosomes:  large,  elliptical  in  shape  and  contain  organized  fibrillar  glycoprotein  matrix  needed  for  eumelanin  synthesisPheomelanosomes:  smaller,  spherical  in  shape,  loose  fibrillar  glycoprotein  matrixFour  stages  of  melanosome  maturation:–  Stage  I  melanosomes  (premelanosomes)▴  Found  in  the  cytoplasm  of  melanocytes▴  Amorphous  matrix;  contain  unprocessed  glycoprotein  known  as  Pmel17  (gp100)–  Stage  II  melanosomes▴  Found  in  the  cytoplasm  of  melanocytes▴  Fully  formed  melanosome  matrix,  fibrils  elongate  and  assemble  into  parallel  sheets▴  Contain  tyrosinase▴  No  active  melanin  synthesis  in  eumelanosomes;  melanin  synthesis  (not  melanogenesis)  in  pheomelanosomes–  Stage  III  melanosomes▴  Found  in  the  cytoplasm  or  dendrites  of  melanocytes▴  Tyrosinase  activity  becomes  positive  and  round  or  oval,  electron  dense,  deposits  of  melanin  found  on  the  internal  filament  network▴  Melanization  begins  at  this  stage–  Stage  IV  melanosomes▴  Found  in  the  cytoplasm  or  dendrites  of  melanocytes▴  Round  or  oval,  electron  opaque▴  Fully  melanized▴  Possess  melanin,  no  enzymatic  activityTyrosinaseCofactor:  copper  (Cu2+)Catalyzes  two  reactions–  Hydroxylation  of  tyrosine  to  DOPA  (dihydroxyphenylalanine)—this  is  the  rate  limiting  step–  Oxidation  of  DOPA  to  DOPAquinone  
SN  - 
PB  - McGraw-Hill Education
CY  - New York, NY
Y2  - 2024/04/19
UR  - dermatology.mhmedical.com/content.aspx?aid=1176106105
ER  -