epidermis

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epidermis
1. (in zoology) The outermost layer of cells of the body of an animal. In invertebrates the epidermis is normally only one cell thick and is covered by an impermeable cuticle. In vertebrates the epidermis is the thinner of the two layers of skin (compare dermis). It consists of a basal layer of actively dividing cells (see Malpighian layer), covered by layers of cells that become impregnated with keratin (see keratinization). The outermost layers of epidermal cells (the stratum corneum) form a water-resistant protective layer. The epidermis may bear a variety of specialized structures (e.g. feathers, hairs).

2. (in botany) The outermost layer of cells covering a plant. It is overlaid by a cuticle and its functions are principally to protect the plant from injury and to reduce water loss. Some epidermal cells are modified to form guard cells (see stoma) or hairs of various types (see piliferous layer). In woody plants the functions of the shoot epidermis are taken over by the periderm tissues (see cork cambium) and in mature roots the epidermis is sloughed off and replaced by the hypodermis.

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ep·i·der·mis / ˌepiˈdərmis/ • n. Biol. the outer layer of cells covering an organism, in particular: ∎  Zool. & Anat. the surface epithelium of the skin of an animal, overlying the dermis. ∎  Bot. the outer layer of tissue in a plant, except where it is replaced by periderm. DERIVATIVES: ep·i·der·mal / -ˈdərməl/ adj. ep·i·der·mic adj. ep·i·der·moid adj.

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epidermis (epi-der-mis) n. the outer layer of the skin, which is divided into four layers (see illustration overleaf). The top three layers are continually renewed as cells from the continuously dividing Malpighian layer are gradually pushed outwards and become progressively impregnated with keratin (see keratinization).
epidermal adj.

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epidermis In animals, outer layer that contains no blood vessels. In many invertebrates, it is only one cell thick. In vertebrates, it may comprise several layers and forms part of the skin. In plants, the epidermis is the outermost layer of a leaf or of an unthickened stem or root; it is usually coated in a waxy layer, the cuticle, which reduces water loss.

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epidermis The outermost layer or layers of cells in an animal. It is one cell thick in many invertebrates, but many cells thick in vertebrates. In land-dwelling vertebrates its surface layer is formed from dead, hardened (keratinized) cells. See also INTEGUMENT.

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epidermis XVII. — late L. — Gr. epidermís, f. EPI- +dérma skin.

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epidermis The outermost layer or layers of cells in a plant or animal. It is one cell thick in plants.

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