The human skin is an organ that forms a protective barrier against germs (and other organisms), dirt and liquids and keeps the inside of your body inside your body, and keeps what’s outside of your body outside. Skin also helps maintain a constant body temperature. Human skin is only about 0.07 inches (2 mm) thick. It is extremely important that the skin stays in optimal condition. Two major causes are responsible for the majority of skin irritation and skin lesions: aging skin and excess of friction.
The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis. The main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells.
Cells are formed through mitosis at the basale layer. The daughter cells move up the strata, changing shape and composition. They eventually reach the stratum corneum and slough off (desquamation). This process is called keratinization and takes place within about 27 days. The keratinized layer of skin acts like a shield and protects the human body. divided into the following 5 sublayers:
Stratum germinativum (also called “stratum basale”)
The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane.
It also harbors many nerve endings that provide the sense of touch and heat. It contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels.
The dermis is structurally divided into two areas: a superficial area adjacent to the epidermis, called thepapillary region, and a deep thicker area known as the reticular region. The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue and receives its name from the dense concentration of collagenous, elastic and reticular fibers. These protein fibers give the dermis its properties of strength, extensibility and elasticity.
The hypodermis lies below the dermis. Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue, elastin and fat. Fat serves as padding and insulation for the body.