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Card 12
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Applied anatomy and physiology


The skin, nails, hair, glands, and associated nerve endings make up the ‘integumentary system’.
Skin.The skin acts as a physical, biochemical, and immunological barrier between the outside world and the body. It also has a role in temperature regulation, synthesis of vitamin D, prevention of water loss, antigen presentation, and sensation.
It is important to remember that the skin also has an important psychosocial function. When we look at another person, we are in fact looking at their skin. As our skin represents our outward appearance to the world, unsightly blemishes, despite their small size, can have a significant impact on a person’s self-esteem.
The skin is made up of three layers - epidermis, dermis, and hypodermis.
Almost 90% of epithelial cells are keratinocytes. These cells are produced in the basal layer and then rise to the surface as more are produced below and the outer cells are shed. The time taken from forming in the basal layer to shedding is usually about three months.
Melanocytes reside in the basal layer and secrete melanin into surrounding keratinocytes via long projections. This, along with the underlying fat and blood, gives the skin its color. In this way, skin tone is determined by the size and number of melanin granules and not by the number of melanocytes.