Formation of stratum corneum and desquamationEpidermis is the outermost layer of skin and it consists of five sublayers. Its main function is to protect underlying tissues and organs from pathogens, toxic agents, oxidants, dehydration, chemicals, environment, ultraviolet radiation and physical stress. Epidermis functions very dynamically and renews continuously.
A continuous process of cell proliferation takes place in the lowermost layer of epidermis known as basale layer. These cells moving outwards undergo maturation and after a number of changes become keratinocyte cells . Eventually these cells die and form the stratum corneum to function as a barrier and get replaced and shed by the desquamation process.
Desmosomes (corneodesmosomes) which are molecular complexes of cell adhesion proteins and cell linking proteins, bind these corneocytes in the outer st. corneum. As these protein complexes move towards outer region of st. corneum, protein degrading proteases, break them up which leads to desquamation.
Function of stratum corneumThis layer functions as a barrier protecting the inner layer of epidermis from dehydration and also from invasion of pathogens. Stratum corneum contain a dense network of a protein known as keratin. Keratin keeps the epidermis hydrated by absorbing moisture as well as by preventing water evaporation.
The st. corneum by the nature of its structure, makes the epidermis elastic and a glutenous protein bond pulls the epidermis back to its original natural shape.
Another important action of S. corneum is in providing protection from mechanical injuries. To carry out this action, this layer is typically thicker in palms and soles. To some extent it helps in the absorption of moisturizers, holding them back from immediate loss.
Effects of defects in stratum corneumThe formation of corneocytes and their desquamation in a regulated manner is very essential for the maintenance of healthy skin. Any failure or set back in these regulated processes can give rise to skin disorders and ailments. A collection of low-molecular-weight water-soluble components, known as the natural moisturizing factor (NMF) present in st. corneum act as a humectant absorbing moisture by direct contact and also from atmosphere.
These barrier and moisturizing properties can be deranged by intrinsic factors like skin diseases and excessive sebum production or xerosis. Extrinsic factors like weather, temperature, low humidity, surfactants and chemicals can also impair the moisturizing barrier. Mental and physical stress can also have effects on the function of stratum corneum cell layers by the increase in the circulating stress hormones in the skin.
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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
Author: Mikael Häggström, based on work by Wbensmith
License: CC BY-SA 3.0
Current topic: Function of the stratum corneum layer cells in skin.