The epidermis and its barrier(s)

Published on June 2, 2014   41 min

Other Talks in the Series: Skin Biology

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Hello. I am Gopi Menon, and I have been involved in research on skin barrier for over 25 years. And it's indeed a privilege and an honor to be presenting this topic for the Henry Stewart series of talks.
Let us start with why barrier is so important and interesting. The outermost layer of skin-- stratum corneum-- is impermeable to water. It prevents efflux and influx of water to and from the body. This barrier allows survival in the dessicating environment on land, while still allowing evaporative cooling. Unlike the other successful land-living organisms, like the insects, which have a rigid cuticle coated with hydrocarbons, mammals developed and evolved a flexible and highly responsive barrier, based on a protein lipid composite structure. The formation and maintenance of this barrier is regulated by a multitude of internal and external factors, and many aspects of these are still being discovered, even as we speak.
Usually, skin talks start with the largest-organ cliche, but, as this assumption has been contested recently, I would say it is perhaps the most important organ and hope that the rest of the presentation will justify that view.
Let me briefly outline the various layers of skin and the epidermis. Skin is formed of several cell types and has four compartments. The outermost epidermis, the basement membrane, the dermis-- that has papillary and reticular layers-- and hypodermis, which is predominantly adipose tissue. Epidermis is anchored to the basement membrane and is composed of keratinocytes, which make up about 95% of epidermis; the rest is melanocytes and dendritic cells, or Langerhans cells. The basal epidermal cells proliferate and differentiate progressively, moving up into the spinous, granular, and cornified layers, in that order, and cornified cells make up the outermost stratum corneum layer.