- Human skin is composed of three layers of tissue.
Human skin serves many purposes. It protects the inside of the body by providing a barrier against things that may hurt the organs, such as heat, germs, and injuries. Skin also helps control body temperature. Nerves in skin enable people to experience the sense of touch and to be able to tell hot from cold. All animals with backbones have skin. All skin does not look alike, though, because some species have features such as feathers or fur attached to their covering. In humans, cells known as melanocytes make a pigment called melanin that creates skin color differences among people. EpidermisThe outer layer of human skin is known as the epidermis. The cells at the surface of this thin layer are constantly being shed by everyday movements such as bathing and putting on clothes. To replace these lost cells, the base of the epidermis is always making new cells. These new cells gradually die as they fill up with a protein called keratin. As they die, they are moved up to the skin surface. It takes about a month for a cell to make its way from the base of the epidermis to the top. The main purpose of the epidermis is to be a protective barrier between the outside world and the inside of the body. Special cells called Langerhans in the epidermis help protect the body against infection. Nails are hardened, thickened epidermis. Likewise, hair is a special type of epidermis. DermisUnderneath the epidermis is the dermis. The main function of this thicker layer is to support and strengthen the epidermis. Fingerlike extensions of the dermis called papillae link the two layers and keep the epidermis in place. A network of blood vessels in the dermis provides nutrients to the epidermis. Most of the dermis consists of tough fiber known as collagen. A second type of fiber, known as elastic fiber, helps the skin to return to its original shape after it has been stretched. The dermis also contains sensory nerves. Subcutaneous fatty layerStoring energy, providing the body with insulation from cold, and cushioning the skin are three important functions of the subcutaneous (meaning “under the skin”) fatty layer. This deepest layer of skin is made up of fat cells, connective tissue, and blood vessels. It also contains hair roots, from which hair growth takes place. GlandsTwo types of glands discharge substances through the skin: sweat glands and oil glands. When the body is overheated, sweat glands send moisture up to pores on the skin's surface; as the sweat evaporates, the body cools. Oil glands, which arise from the walls of hair follicles, produce an oil called sebum that lubricates the skin and hair. Skin problemsVarious things can harm skin or cause it to become irritated. Viruses can cause skin blisters known as shingles. Extra oil production during the teenage years makes many in this age group suffer a skin inflammation known as acne. Allergic reactions to foods, chemicals, plants, and other substances may cause a person's skin to become red, bumpy, or itchy. Being in the sun for too long can cause the skin to burn and can be a factor in causing skin cancer. To avoid these problems, doctors recommend limiting the time one spends in the sun, covering the body with special lotion that blocks out harmful rays, and wearing a hat and other clothing that can keep the skin from being directly exposed to the sun. |