huidepitheel

Huidepitheel, or epidermis, is the outermost layer of the skin. It is a stratified squamous epithelium that rests on a basement membrane and is avascular, obtaining nutrients by diffusion from the underlying dermis. Thickness varies, with thick skin on the palms and soles and thinner skin elsewhere.

The epidermis consists of several layers: stratum basale, stratum spinosum, stratum granulosum, and, in thick skin, stratum lucidum, ending with the stratum corneum. The major cell type is the keratinocyte, which produces keratin as it migrates toward the surface. Other cells include melanocytes (pigment producers), Langerhans cells (immune defenders), and Merkel cells (mechanoreceptors).

Functions include forming a protective barrier against mechanical damage, pathogens, and chemical exposure, preventing transepidermal water loss, and participating in immune responses and vitamin D synthesis. The stratum corneum provides the waterproof outer surface, while keratinocyte renewal maintains epidermal integrity. Renewal typically cycles about every 28 days in adults.

Developmentally, the epidermis arises from ectoderm. It also forms skin appendages such as hair, nails, and glands (eccrine, apocrine, and sebaceous) that originate from epidermal invaginations.

Clinical relevance includes disorders that compromise barrier function, such as dermatitis and psoriasis, as well as ichthyosis and epidermolysis bullosa, which involve abnormalities in keratinization or cell adhesion. Diagnosis and understanding of epidermal conditions often rely on histology and clinical examination.