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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 epidermal 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.
The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue guarding muscles, bones, ligaments and internal organs. Human skin is similar to most of the other mammals' skin, and it is very similar to pig skin.
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 tonofibrils go on to form the desmosomes, which allow for strong connections to form between adjacent keratinocytes. The stratum spinosum also contains Langerhans cells, which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer. [6] [7] [8]
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 ...
Some skin secretions are associated with body hair. Skin secretions originate from glands that in dermal layer of the epidermis. Sweat, a physiological aid to body temperature regulation, is secreted by eccrine glands. Sebaceous glands secrete the skin lubricant sebum. Sebum is secreted onto the hair shaft and it prevents the hair from splitting.
Layers of corneocytes produce high mechanical strength which allows epidermis of the skin to perform its function as a physical, chemical and immunological barrier. For example, corneocytes act as UV barrier by reflecting the scattered UV radiation, protecting cells inside the body from apoptosis and DNA damage. [ 8 ]
Skin sloughing is the process of shedding dead surface cells from the skin. It is most associated with cosmetic skin maintenance via exfoliation , but can also occur biologically or for medical reasons.