The skin is far more than just the outer covering of human beings; it is an organ just like the heart, lung, or liver. Besides providing a layer of protection from pathogens, physical abrasions, and radiation from the sun, the skin serves many functions. It plays a vital role in homeostasis by maintaining a constant body temperature via the act of sweating or shivering and by making you aware of external stimuli through information perceived within the touch receptors located within the integumentary system. It only takes one visit to a burn unit to see the value of skin and the many complications that arise when this organ is compromised.
The skin, or integument, is considered an organ because it consists of all four tissue types. The skin also consists of accessory organs, such as glands, hair, and nails, thus making up the integumentary system. A section of skin with various accessory organs is shown in Figure 1.
Figure 1 .A section of skin with various accessory organs.
The skin consists of two layers, the epidermis and the underlying dermis. Although technically not part of the skin, the hypodermis (subcutaneous layer, or superficial fascia) lies beneath the dermis.
The skin performs a variety of functions:
- Protection is provided against biological invasion, physical damage, and ultraviolet radiation.
- Sensation is provided by nerve endings for touch, pain, and heat.
- Thermoregulation is supported through the sweating and regulation of blood flow through the skin.
- Synthesis of vitamin D occurs in the skin.
- Blood within the skin can be shunted to other parts of the body when needed.
- Excretion of salts and small amounts of wastes (ammonia and urea) occurs with the production of sweat.