Epidermis

: The upper or outer layer of the two main layers of cells that make up the skin. The epidermis is mostly made up of flat, scale-like cells called squamous cells. Under the squamous cells are round cells called basal cells. The deepest part of the epidermis also contains melanocytes. These cells produce melanin, which gives the skin its color. The other main layer of the skin is the dermis, the inner layer of skin, that contains blood and lymph vessels, hair follicles, and glands. These glands produce sweat, which helps regulate body temperature, and sebum, an oily substance that helps keep the skin from drying out. Sweat and sebum reach the skin's surface through tiny openings called pores.

* * *

1. The superficial epithelial portion of the skin (cutis). The thick e. of the palms and soles contains the following strata from the surface : stratum corneum (keratin layer), stratum lucidum (clear layer), stratum granulosum (granular layer), stratum spinosum (prickle cell layer), and stratum basale (basal cell layer); in other parts of the body, the stratum lucidum may be absent. 2. In botany, the outermost layer of cells in leaves and the young parts of plants. SYN: cuticle (3), cuticula (2), epiderm, epiderma. [G. e., the outer skin, fr. epi, on, + derma, skin]

* * *

epi·der·mis -'dər-məs n

1) the outer epithelial layer of the external integument of the animal body that is derived from the embryonic epiblast specif the outer nonsensitive and nonvascular layer of the skin of a vertebrate that overlies the dermis

2) any of various animal integuments

* * *

n.

the outer layer of the skin, which is divided into four layers. The innermost Malpighian or germinative layer (stratum germinativum) consists of continuously dividing cells. The other three layers are continually renewed as cells from the germinative layer are gradually pushed outwards and become progressively impregnated with keratin (see keratinization). The outermost layer (stratum corneum) consists of dead cells whose cytoplasm has been entirely replaced by keratin. It is thickest on the soles of the feet and palms of the hands.

• epidermal adj.

* * *

epi·der·mis (ep″ĭ-durґmis) pl. epiderґmides [epi- + dermis] [TA] the outermost, nonvascular layer of the skin, derived from the embryonic ectoderm, varying in thickness from 0.07 to 0.12 mm, except on the palms and soles where it may be 0.8 to 1.4 mm. On the palms and soles it exhibits maximal cellular differentiation and layering, and comprises, from within outward, five layers: the stratum basale (basal layer); the stratum spinosum (prickle cell or spinous layer); the stratum granulosum (granular layer); the stratum lucidum (clear layer); and the stratum corneum (horny layer). In the thinner epidermis of the general body surface, the stratum basale, stratum spinosum, and stratum corneum are constantly present and the stratum granulosum is usually identifiable, but the stratum lucidum is usually absent.

Section of epidermis.