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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.
Human skin pigmentation varies substantially between populations; this has led to the classification of people(s) on the basis of skin colour. [3] In terms of surface area, the skin is the second largest organ in the human body (the inside of the small intestine is 15 to 20 times larger).
It forms the outermost layer of the skin and the inner lining of the mouth, esophagus and vagina. [2] In the epidermis of skin in mammals, reptiles, and birds, the layer of keratin in the outer layer of the stratified squamous epithelial surface is named the stratum corneum. Stratum corneum is made up of squamous cells which are keratinized and ...
Histologic image showing a section of epidermis. Stratum spinosum labeled slightly below center. The stratum spinosum (or spinous layer/prickle cell layer) [1] is a layer of the epidermis found between the stratum granulosum and stratum basale. [2] This layer is composed of polyhedral keratinocytes. [3] [4] These are joined with desmosomes. [3]
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 ...
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.
Histologic image of the epidermis with its layers named in white text.. The Malpighian layer (stratum mucosum or stratum malpighii) of the epidermis is generally defined as both the stratum basale (basal layer) and the thicker stratum spinosum (spinous layer/prickle cell layer) immediately above it as a single unit, [1] [2] although it is occasionally defined as the stratum basale specifically ...
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.