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#AnatomyFactoid: Did you know that the epidermis is the outer layer of skin (the inner layer is the dermis). The epidermis acts as a barrier to infection from environmental pathogens and regulates the amount of water lost from the body through evaporation (or transepidermal water loss). The epidermis is thinnest on the eyelids and thickest on the palms of the hands and soles of the feet. The epidermis is composed of five layers known as strata. Thus, from the top down, the layers are: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale.

The stratum corneum (i.e., cornified layer) is composed of many (10-30) layers of flattened, anucleated corneocytes surrounded by keratin (a protective protein). [Your hair and nails are also made of keratin.] Most of the barrier function of the epidermis comes from the stratum corneum.

The stratum lucidum (i.e., clear layer) is the translucent layer. [This layer is found only in the palms and soles.]

The stratum granulosum (i.e., granular layer) consists of anuclear keratinocytes. The cytoplasm of these cells appears granular (hence the name of this layer).

The stratum spinosum (i.e., spinous layer) contains active immune (i.e., Langerhans) cells.

The stratum basale (i.e., basal/germinal layer) is composed of large numbers of melanocytes containg the protein melanin. [Melanin is the pigmented protein that gives your skin its color.] New keratinocytes are produced (i.e., "germinate") in this layer and these cells migrate upwards to eventually replace the cells in the other layers. The columnar cells of the stratum basale are anchored to the basement membrane and are associated with cutaneous nerves to provide the sensation of light touch.

Many anatomy topics are best remembered through the use of mnemonics. Here is an effective mnemonic for remembering the layers of the epidermis: "Careless Loungers Get Sun Burned."