RT Book, Section
A1 Kubo, Akiharu
A1 Amagai, Masayuki
A2 Kang, Sewon
A2 Amagai, Masayuki
A2 Bruckner, Anna L.
A2 Enk, Alexander H.
A2 Margolis, David J.
A2 McMichael, Amy J.
A2 Orringer, Jeffrey S.
SR Print(0)
ID 1161321454
T1 Skin Barrier
T2 Fitzpatrick's Dermatology, 9e
YR 2019
FD 2019
PB McGraw-Hill Education
PP New York, NY
SN 9780071837798
LK accessmedicine.mhmedical.com/content.aspx?aid=1161321454
RD 2024/04/19
AB AT-A-GLANCEOne  of  the  most  important  functions  of  the  skin  is  to  form  a  barrier  between  the  organism  and  the  external  environment.The  skin  protects  our  bodies  from  physical  damage  caused  by  desiccation,  physical  stress,  infection,  overheating  or  heat  loss,  and  ultraviolet  (UV)  irradiation.The  skin  is  covered  by  the  epidermis,  a  cornified,  stratified  epithelial  cellular  sheet  that  is  equipped  with  a  barrier  formed  by  the  stratum  corneum  and  tight  junctions.The  stratum  corneum  is  an  air–liquid  interface  barrier  on  the  body  surface  that  prevents  excessive  water  loss  (inside–outside  barrier)  and  the  entry  of  harmful  substances  from  the  environment  (outside–inside  barrier).The  stratum  corneum  barrier  is  composed  of  corneocytes  and  intercorneocyte  water-impermeable  lipid  lamellae.  Corneocytes  are  wrapped  with  cornified  cell  envelope  and  corneocyte  lipid  envelope  and  contain  keratin  filaments  associated  with  filaggrin,  which  is  degraded  to  natural  moisturizing  factors.The  tight  junctions  seal  the  intercellular  space  between  neighboring  cells  at  the  second  layer  in  the  stratum  granulosum  and  form  a  liquid–liquid  interface  barrier  that  limits  molecular  movement  through  the  paracellular  pathway.Langerhans  cells  are  located  in  the  epidermis  under  the  tight  junction  barrier  in  steady  state  but  extend  their  dendrites  to  the  outside  tight  junction  barrier  upon  activation  to  capture  external  antigens  at  the  tips  of  the  dendrites.Antimicrobial  peptides,  lipids,  the  acidic  pH  of  the  stratum  corneum,  and  continuous  daily  desquamation  (daily  detachment  of  dead  skin  cells)  control  the  skin  microbiota  and  protect  us  from  infection  by  bacteria,  yeasts,  fungi,  and  virusesUV  light  is  reflected  from  the  stratum  corneum  and  absorbed  by  urocanic  acid  and  melanin  molecules,  which  protect  genomic  DNA  from  UV  irradiation  damage.Sweating,  blood  flow  control,  and  heat  storage  in  subcutaneous  adipose  tissue  protect  us  from  cold  and  overheating.