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Most of the barrier functions of the epidermis localize to this layer. [12] clear/translucent layer (stratum lucidum, only in palms and soles) This narrow layer is found only on the palms and soles. The epidermis of these two areas is known as "thick skin" because with this extra layer, the skin has 5 epidermal layers instead of 4.
The epidermis, "epi" coming from the Greek language meaning "over" or "upon", is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface, which also serves as a barrier to infection and is made up of stratified squamous epithelium with an underlying basal lamina.
The epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialized parenchyma cells, [1] but the established modern preference has long been to classify the epidermis as dermal tissue, [2] whereas parenchyma is classified as ground tissue. [3]
In general, it is found where absorption and filtration occur. The thinness of the epithelial barrier facilitates these processes. [3] In general, epithelial tissues are classified by the number of their layers and by the shape and function of the cells. [1] [3] [4] The basic cell types are squamous, cuboidal, and columnar, classed by their shape.
The epidermis is regenerated from the stem cells found in the basal layer that develop into the corneum. The epidermis itself is devoid of blood supply and draws its nutrition from its underlying dermis. [5] Its main functions are protection, absorption of nutrients, and homeostasis.
Keratinized epithelium has keratin deposited on the surface which makes it impermeable and dry. Examples of keratinized stratified squamous epithelium include skin, the epidermis of the palm of the hand, and the sole of the foot, [3] and the masticatory mucosa.
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 mammalian epidermis always possesses at least a stratum germinativum and stratum corneum, but the other intermediate layers found in humans are not always distinguishable. Hair is a distinctive feature of mammalian skin, while feathers are (at least among living species) similarly unique to birds .