Monday, January 21

Epidermis parts - Five layers of epidermal skin in order

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Epidermis is the outermost of the two layers of skin. Epidermal skin is made up of five parts (sublayers).
Its structure is made up of keratinocytes, melanocytes, Langerhans cells and Merkel cells and the majority of them (about 90%) being keratinocytes.

Five layers of epidermis in descending order

Starting from outermost region it is divided into the following five parts or strata in the following order:
  1. Stratum corneum
  2. Stratum lucidum
  3. Stratum granulosum
  4. Stratum spinosum
  5. Stratum basale (also called "stratum germinativum")
Epidermis is avascular (having no blood vessels) and is nourished  by the dermis by diffusion. There is continuous mitotic cell division process going on in keratinocytes in the deepest part of this layer. Each keratinocyte divides into two identical daughter cells of which one remains to carry on the next mitotic cell division and the other one migrates upwards. The older cells are pushed upward and in this process move away from the nourishing dermis. With the loss of nourishment they die and get flattened to form many layers of dead cells, eventually getting sloughed off.

The melanocytes are present in the deepest part and they produce and transfer the skin pigment to the surrounding keratinocytes. Langerhans cells detect the intruding foreign bodies and transport them to lymphocytes present in dermis. Merkel cells present at the deepest part of epidermis function as mechanoreceptors.
Reference:
1.Harding, C. R. (2004), The st. corneum: structure and function in health and disease. Dermatologic Therapy, 17: 6–15. doi: 10.1111/j.1396-0296.2004.04S1001.x
Image source:
http://en.wikipedia.org/wiki/File:Skinlayers.png
Author: Serephine
License: Public domain

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