Epidermis

Definition

The outermost cellular layer of the integument, lying above the dermis or basement membrane, that serves as the primary interface between an organism and its environment. In arthropods, the epidermis (often called the hypodermis in older literature) is a single layer of epithelial cells that secretes the overlying cuticle, coordinates molting through apolysis and ecdysis, and contains sensory and glandular structures. The term is also used for the analogous outer epithelial layer in vertebrates and other animal phyla.

Etymology

Greek epi- (upon, over) + derma (skin)

Example

In a caterpillar preparing to molt, the epidermis detaches from the old cuticle (apolysis), secretes molting fluid to digest the old endocuticle, and then generates a new cuticle beneath before ecdysis.

Synonyms

• hypodermis (arthropods, historical usage)
• integumentary epithelium

Related Terms

• Cuticle
• dermis
• hypodermis
• apolysis
• Ecdysis
• Exoskeleton
• Integument
• Basement membrane
• epicuticle

Usage Notes

In vertebrate anatomy, 'epidermis' refers to the keratinized outer skin layer; in arthropodology, the same cell layer is frequently termed 'hypodermis' in older texts, though modern usage increasingly standardizes on 'epidermis' for the secretory epithelium beneath the cuticle. The arthropod epidermis is not itself the hard exoskeleton, but the living tissue that produces it. Contrast with 'dermis' (connective tissue layer in vertebrates) and 'hypodermis' (subcutaneous fat layer in vertebrates; or the epidermal layer itself in some arthropod literature).