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The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the stratum disjunctum and stratum compactum. The skin's protective acid mantle and lipid barrier sit on top of the stratum disjunctum. [5] The stratum disjunctum is the uppermost and loosest layer of skin.
The lipids ultimately form the lamellar lipid bilayer that surrounds corneocytes and also contributes to the permeability barrier homeostasis of the stratum corneum. [12] The homeostasis function is regulated by the calcium gradient in the epidermis. [17] Usually the calcium level is very low in stratum corneum, but high in stratum granulosum.
The stratum corneum is the outermost layer of the epidermis and the rate-limiting barrier in absorption of an agent. [4] Thus, how quickly something passes through this thicker outer layer determines the overall absorption. The stratum corneum is primarily composed of lipophilic cholesterol, cholesterol esters and ceramides. Thus lipid-soluble ...
In normal skin, the rate of keratinocyte production equals the rate of loss, [4] taking about two weeks for a cell to journey from the stratum basale to the top of the stratum granulosum, and an additional four weeks to cross the stratum corneum. [2] The entire epidermis is replaced by new cell growth over a period of about 48 days. [13]
After reaching the top layer stratum corneum they are eventually 'sloughed off', or desquamated. This process is called keratinization and takes place within weeks. It was previously believed that the stratum corneum was "a simple, biologically inactive, outer epidermal layer comprising a fibrillar lattice of dead keratin". [9]
Stratum corneum's function includes prevention of water loss in skin and inhibit the penetration of foreign molecules into the dermal layers. [8] Hence, it also prevents the hydrophilic molecules to get absorbed into the skin since it is made out of bilayered lipids. [9] With this barrier, stratum corneum affects
A calcium gradient, with the lowest concentration in the stratum basale and increasing concentrations until the outer stratum granulosum, where it reaches its maximum. Calcium concentration in the stratum corneum is very high in part because those relatively dry cells are not able to dissolve the ions. [10]
They form several layers of the skin. Life for a keratinocyte begins at the stratum basale layer. Cells here proliferate and move through the stratum spinosum and stratum granulosum. The topmost layer is called the stratum corneum. During sloughing, it is this layer that is removed. [1]