Sunday, January 6

Basal cell layer of epidermal skin - Stratum basale (germinativum)

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Basal cell layer of skin (aka stratum basale or germinativum) is the lowermost sublayer of epidermis. This layer of basal cells is made up of one row of constantly dividing columnar or cubical undifferentiated keratinocytes.
This region is separated from the lower dermis by basement membrane and is attached to the basement membrane through hemidesmosomes.

Structure of basal cell layer

Stratum basale is usually one keratinocyte deep with melanocytes and Langerhans or immune cells dispersed in between. These melanocytes synthesize melanin pigment, giving color and hue to the skin and the hair. The amount of melanin produced though predetermined genetically, is affected by sun exposure levels leading to increase or decrease in production. The Merkel nerve endings (neuroectodermal origin) which have tactile or touch sensation function are also dispersed in this germinativum epidermis. As this basal stratum is in close contact with dermis, it is nurtured with oxygen and nutrients by dermis by diffusion process.

Functions of basal cell layer

High degree of mitosis or cell proliferation activity is found in this basal region and hence the name 'germinativum' (germinating). This cuboid keratinocyte divides into two daughter keratinocytes and the upper keratinocyte migrates towards outer epidermal layers undergoing progressive transformation called keratinisation. After moving into stratum spinosum, these keratinocytes change shape and become polygonal and start synthesizing keratin. Keratinocytes produce more and more keratin and eventually undergo programmed death (apoptosis). In humans, it is estimated that basal stratum turnover from epidermal proliferation units to desquamation every 40–56 days.

The lower basal daughter keratinocyte remains in the stratum basale and undergoes growth and maturation for the next mitosis. As the stratum cornium is continuously sloughed off, the mitosis and replacement activity at basal region should continuously go on. The proliferation and differentiation of basal epidermal region is regulated by Vitamin D3 (cholecalciferol).

Any chemical, physical, physiological, radiological or pathgenic disturbance of this cell proliferation activity at basal germinativum brings about dermal ailments.
Reference:
Harding, C. R. (2004), The stratum 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:Epidermal_layers.png
Author:Mikael Häggström, based on work by Wbensmith
License: CC BY-SA 3.0

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