Lists of diseases: List of mental disorders as defined by the DSM and ICD, List of genetic disorders, List of neurological disorders, List of diseases, List of notifiable diseases, List of cutaneous conditions, List of dog diseases

Source: Wikipedia. Pages: 121. Chapters: List of mental disorders as defined by the DSM and ICD, List of genetic disorders, List of neurological disorders, List of diseases, List of notifiable diseases, List of cutaneous conditions, List of dog diseases, List of fictional diseases, List of hematologic conditions, List of eponymous diseases, List of parasites of humans, Eye disease, List of systemic diseases with ocular manifestations, List of cancer types, Nutrition disorder, List of circulatory system conditions, List of diseases caused by insects, List of disorders, List of childhood diseases and disorders. Excerpt: Many conditions affect the human integumentary system¿the organ system covering the entire surface of the body and is composed of skin, hair, nails, and related muscle and glands. The major function of this system is as a barrier against the external environment. The skin weighs an average of four kilograms, covers an area of two square meters, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. There are two main types of human skin: glabrous skin, the nonhairy skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin. Within the latter type, there are hairs in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle. In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues. 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. Nourishment is provided to these layers via diffusion from the dermis, since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis. This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface. In normal skin, the rate of production equals the rate of loss; it takes about two weeks for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum. The dermis is the layer of skin between the epidermis