epidermis

—epidermal, epidermic, adj. —epidermically, adv.

/ep'i derr"mis/, n.

1. Anat. the outer, nonvascular, nonsensitive layer of the skin, covering the true skin or corium.

2. Zool. the outermost living layer of an animal, usually composed of one or more layers of cells.

3. Bot. a thin layer of cells forming the outer integument of seed plants and ferns.

[1620-30; < LL: surface skin < Gk epidermís upper skin. See EPI-, DERMA]

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▪ anatomy

  in zoology, protective outermost portion of the skin. There are two layers of epidermis, the living basal layer, which is next to the dermis, and the external stratum corneum, or horny layer, which is composed of dead, keratin-filled cells that have migrated outward from the basal layer. The melanocytes, responsible for skin colour, are found in the basal cells. The epidermis has no blood supply and depends on diffusion from the dermal cells for its metabolic needs. The dead-cell layer of the stratum corneum provides the protection from water loss that allows vertebrates to dwell on land. keratin, produced in migrating epidermal cells, forms the basis of nails, feathers, beaks, and other epidermal derivatives. In humans, epidermal fragments are constantly shed, but the “skin,” or stratum corneum, of a snake is ordinarily shed all at once in a period of ecdysis.

▪ plant tissue

      in botany, outermost, protoderm-derived layer of cells covering the stem, root, leaf, flower, fruit, and seed parts of a plant. The epidermis and its waxy cuticle provide a protective barrier against mechanical injury, water loss, and infection. Various modified epidermal cells regulate transpiration, increase water absorption, and secrete substances.

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