Epidermis
This is the top layer of skin made up of epithelial cells. It does not contain blood vessels. Its main function is protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized stratified squamous epithelium comprising four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans' cells. The major cell of the epidermis is the keratinocyte, which produces keratin. Keratin is a fibrous protein that aids in protection. Keratin is also a water-proofing protein. Millions of dead keratinocytes rub off daily. The majority of the skin on the body is keratinized, meaning waterproofed. The only skin on the body that is non-keratinized is the lining of skin on the inside of the mouth. Non-keratinized cells allow water to "stay" atop the structure.
The protein keratin stiffens epidermal tissue to form fingernails. Nails grow from thin area called the nail matrix; growth of nails is 1 mm per week on average. The lunula is the crescent-shape area at the base of the nail, this is a lighter color as it mixes with the matrix cells.
Read more about this topic: Integumentary System, Layers of The Skin
Famous quotes containing the word epidermis:
“Allusion has been made to [Proust’s] contempt for the literature that “describes,” for the realists and naturalists worshipping the offal of experience, prostrate before the epidermis and the swift epilepsy, and content to transcribe the surface, the façade, behind which the Idea is prisoner.”
—Samuel Beckett (1906–1989)