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The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. [1] The epidermal layer provides a barrier to infection from environmental pathogens [2] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.
Micrograph of keratinocytes, basal cells and melanocytes in the epidermis Keratinocytes (stained green) in the skin of a mouse. Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. [1]
The main type of cells that make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in palms of hands and bottoms of feet), granulosum, spinosum, and basale. Cells are ...
The clear epidermal cells exist in a single layer and do not contain chloroplasts, because the onion fruiting body (bulb) is used for storing energy, not photosynthesis. [3] Each plant cell has a cell wall, cell membrane, cytoplasm, nucleus, and a large vacuole. The nucleus is present at the periphery of the cytoplasm.
Others serve to anchor the epidermis glabrous skin (hairless), and hyper-proliferative epidermis (from a skin disease). [1] They divide to form the keratinocytes of the stratum spinosum, which migrate superficially. [2] Other types of cells found within the stratum basale are melanocytes (pigment-producing cells) and Merkel cells (touch receptors).
The stratum corneum (Latin for 'horned layer') is the outermost layer of the epidermis. Consisting of dead tissue, it protects underlying tissue from infection, dehydration, chemicals and mechanical stress. It is composed of 15–20 layers of flattened cells with no nuclei and cell organelles.
Histologic image showing a section of epidermis. Stratum spinosum labeled slightly below center. The stratum spinosum (or spinous layer/prickle cell layer) [1] is a layer of the epidermis found between the stratum granulosum and stratum basale. [2] This layer is composed of polyhedral keratinocytes. [3] [4] These are joined with desmosomes. [3]
The stratum granulosum (or granular layer) is a thin layer of cells in the epidermis lying above the stratum spinosum and below the stratum corneum (stratum lucidum on the soles and palms). [1] Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in this layer.