Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis.
The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Nourishment is provided to these layers by diffusion from the dermis since the epidermis is without direct blood supply. 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. 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. Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle.
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The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin.
The skin weighs an average of four kilograms, covers an area of two square metres, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue. The major function of this system is as a barrier against the external environment. “It is very interesting to me to see the range of the fields that can benefit from application of memristor theory.Many conditions affect the human integumentary system-the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands. Williams, meanwhile, is gratified by the interest in memristors.
Resistance to alternating current is already used to diagnose skin abnormalities, says Johnsen’s colleague Andrew Lütken. The involvement of skin in regulatory processes can be considered a form of primitive intelligenceĪ new understanding of skin’s electrical properties could have implications for medicine. Whether this behaviour helps skin function isn’t clear but Yuriy Pershin of the University of South Carolina in Columbia, who has studied memristive behaviour in amoebas, describes the skin’s role in processes such as temperature regulation as “primitive intelligence”. Conversely, a positive potential pushes the ions back, thinning the layer of sweat lining the pore walls and increasing the skin’s resistance to current. The longer skin is exposed to a negative potential, the lower the subsequent resistance, until it maxes out when sweat fills the pore. As sweat is highly conductive, extra fluid rising to the surface increases skin’s surface conductivity and thereby lowers its resistance if a subsequent potential is applied. Although a thin layer of fluid always coats the inside of the cylindrical pore, this layer thickens as the sweat rises. When skin is exposed to a negative potential, the fluid at the bottom of the sweat pores is drawn upward. Sweat contains positively charged ions such as sodium. The researchers attribute skin’s memristor behaviour to sweat pores.
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