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The stratum lucidum (Latin, 'clear layer') is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is readily visible by light microscopy only in areas of thick skin , which are found on the palms of the hands and the soles of the feet.
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.
In normal skin, the rate of keratinocyte production equals the rate of loss, [4] taking about two weeks for a cell to journey from the stratum basale to the top of the stratum granulosum, and an additional four weeks to cross the stratum corneum. [2] The entire epidermis is replaced by new cell growth over a period of about 48 days. [13]
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. It consists mostly of lipids.
The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. [8] Nourishment is provided to these layers by diffusion from the dermis since the epidermis is without direct blood supply.
Eleidin is clear intracellular protein which is present in the stratum lucidum of the skin. Eleidin is a transformation product of the amino acid complex keratohyalin, the lifeless matter deposited in the form of minute granules within the protoplasm of living cells. Eleidin is then converted to keratin in the stratum corneum.
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] Basal cells in the basal layer (stratum basale) of the skin are sometimes referred to as basal keratinocytes. [2]
Apocrine glands produce a fatty secretion, thus giving away an odorous smell. These are located in the inguinal and axillary regions of the body, and include the mammary glands. These are located in the inguinal and axillary regions of the body, and include the mammary glands.