Skin, hair and nails: the integumentary system

The integumentary system is the body's outer covering, made up of the skin together with structures derived from it such as hair, nails and various glands. As the largest organ of the body, the skin forms a protective barrier against injury, water loss and infection, helps regulate body temperature, and contains the receptors that provide the sense of touch. The medical study of the skin and its disorders is called dermatology.

The skin has two main layers. The outer layer, the epidermis, is composed largely of cells called keratinocytes that produce keratin, a tough protein that makes the surface water-resistant and resilient. The epidermis constantly renews itself: new cells form at its base and are pushed outward, dying and flaking off at the surface. Scattered among the basal cells are melanocytes, which produce the pigment melanin that gives skin its colour and helps shield deeper tissue from ultraviolet light. Beneath the epidermis lies the dermis, a thicker layer of connective tissue containing blood vessels, nerves, hair follicles and the glands of the skin, including the sweat and oil glands.

Hair and nails are specialised products of the skin, both built mainly from keratin. Each hair grows from a follicle rooted in the dermis, where dividing cells push the hair shaft outward. Nails grow from a region called the matrix at the base of the nail, and the same keratin that hardens them gives them their strength. Together the layers and appendages of the integumentary system protect the body, sense the environment, and help maintain a stable internal state.

Frequently asked questions

What are the two main layers of skin?

The outer layer is the epidermis, which forms the protective surface, and beneath it lies the dermis, a thicker layer holding blood vessels, nerves, glands and hair follicles.

What does melanin do?

Melanin is the pigment made by melanocytes that gives skin and hair their colour and helps protect deeper cells from ultraviolet radiation.

What is keratin?

Keratin is a tough, fibrous protein that makes up the surface of the skin and forms the bulk of hair and nails, giving them strength and water resistance.