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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.
The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue guarding muscles, bones, ligaments and internal organs. Human skin is similar to most of the other mammals' skin, and it is very similar to pig skin.
Some skin secretions are associated with body hair. Skin secretions originate from glands that in dermal layer of the epidermis. Sweat, a physiological aid to body temperature regulation, is secreted by eccrine glands. Sebaceous glands secrete the skin lubricant sebum. Sebum is secreted onto the hair shaft and it prevents the hair from splitting.
In humans, they constitute 90% of epidermal skin cells. [1] Basal cells in the basal layer ( stratum basale ) of the skin are sometimes referred to as basal keratinocytes . [ 2 ] Keratinocytes form a barrier against environmental damage by heat , UV radiation , water loss , pathogenic bacteria , fungi , parasites , and viruses .
Sampling of human stratum corneum using a tape-stripping method [1] 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 ...
Histologic image showing a section of epidermis. Stratum basale labeled near bottom. The stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest layer of the five layers of the epidermis, the external covering of skin in mammals. The stratum basale is a single layer of columnar or cuboidal basal cells.
In humans, for example, the skin located under the eyes and around the eyelids is the thinnest skin on the body at 0.5 mm thick and is one of the first areas to show signs of aging such as "crows feet" and wrinkles. The skin on the palms and the soles of the feet is the thickest skin on the body at 4 mm thick.
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.