One or more layers of cells forming the outermost portion of the skin or integument
In humans, the skin is the largest organ of the integumentary system. The role of the skin is vital as it protects the body (especially the underlying tissues) against pathogens and excessive water loss. It is also involved in providing insulation, temperature regulation and sensation. The skin of humans and other mammals is composed of two major layers: (1) epidermis and (2) dermis. The epidermis is the outer, waterproofed layer of the skin and the dermis is the layer below the epidermis. In between the two layers is a thin sheet of fibers called the basement membrane.
The epidermis is a protective outer covering of many plants and animals. It may be comprised of a single layer, as in plants, or of several layers of cells on top of the dermis, as in those of vertebrate animals. The primary role of the epidermis is to protect the more susceptible layers of the skin.
In plants, the epidermal cells secrete further protective substance (called cuticle) to prevent desiccation (water loss). A plant leaf is lined with two layers of epidermis (i.e. upper and lower): one on top of and another one below the mesophyll layer.
In animals, such as vertebrates, the epidermis is made up of several layers to protect the underneath layers from physical damage, infection, and water loss. In humans, for instance, the epidermis consists of layers (strata) such as the following:
- stratum corneum
- stratum lucidum
- stratum granulosum
- stratum spinosum
- stratum basale (or stratum germinativum)
Word origin: epi– (on top of) + derma (skin)
- epidermal (adjective, of, pertaining to, or characterized by epidermis)
- epidermic adjective, relating to the (outermost) skin