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The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. [1] The epidermis layer provides a barrier to infection from environmental pathogens [2] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.
In the process, however, keratinocytes are killed. If the keratinocytes that apoptose are in the lowest layer of the skin, this can be an issue. Typically, however, keratinocytes in higher layers are able to slough away normally. The skin peeling that occurs as sunburns heal is due to this process.
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 dermis is composed of three major types of cells: [3] fibroblasts, macrophages, and mast cells.. Apart from these cells, the dermis is also composed of matrix components such as collagen (which provides strength), elastin (which provides elasticity), and extrafibrillar matrix, an extracellular gel-like substance primarily composed of glycosaminoglycans (most notably hyaluronan ...
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] It is now understood that this is not true, and that the stratum corneum should be considered to be a live tissue ...
The skin weighs an average of four kilograms, covers an area of two square metres, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. [1] The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. [3]
In the event of an injury that damages the skin's protective barrier, the body triggers a response called wound healing. After hemostasis, inflammation white blood cells, including phagocytic macrophages arrive at the injury site. Once the invading microorganisms have been brought under control, the skin proceeds to heal itself.
This layer is composed of polyhedral keratinocytes. [3] [4] These are joined with desmosomes. [3] Their spiny (Latin, spinosum) appearance is due to shrinking of the microfilaments between desmosomes that occurs when stained with H&E. Keratinization begins in the stratum spinosum, [5] although the actual keratinocytes begin in the stratum ...