Skin Facts – Functions
The human skin is an amazing organ; it is the largest organ in the human body, and equates to approximately 15% of our total body weight; it is our outer covering, and protects the underlying muscles, bones and internal organs. Because it is our barrier to the environment it plays an important role in ensuring that we remain protected from pathogens and that we do not lose too much water.
Our skin performs the following functions:
- Protection: Our skin is the anatomical barrier between the internal and external environment and aids our bodily defences to protect us from pathogens and damage; Langerhans cells (part of the bodies adaptive immune system) are located in the epidermis and the dermis. They monitor the surface of the skin for attacks from bacteria, viruses and also help to fight off injuries.
- Sensation: The skin has a multitude of sensory receptors (nerve endings) that react to different stimuli such as touch, pressure, temperature, vibration or pain. The density of these receptors varies from one part of the body to another; there are 2,500 receptors per cm2 just on the fingertips.
- Heat regulation: The skin in effect is your bodies’ thermostat, and contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. During hot weather the skin induces sweating, this dilates blood vessels in the skin to increase blood flow, which further increases perfusion and therefore heat loss. During cold weather the skin induces shivering, which contracts blood vessels in the skin to decrease blood flow, this prevents unnecessary heat loss to conserve body warmth.
- Aesthetics and communication: Our skin can communicate to others our mood or the way we are feeling. For instance, when we experience a sudden and strong emotion, such as embarrassment or stress, this causes the sympathetic nervous system to widen blood vessels in the face. This increases the blood flow to the skin, producing the redness associated with blushing. Others assess our attractiveness in a number of ways, and one important factor is our skin. How others see us is a very personal thing, and what is attractive to one is not necessarily attractive to another.
- Storage and synthesis: The skin acts as a storage centre for lipids (fat) and water. Water is held to prevent the skin from drying out, while the lipids help to form a natural skin barrier, which holds in moisture and keeps out dirt and impurities. Exposing the skin to sunlight is the primary source of vitamin D for most people. Solar ultraviolet-B radiation (UVB) stimulates the production of vitamin D3 from 7-dehydrocholesterol (7-DHC) in the epidermis of the skin.
- Excretion: Our sweat is composed of about 98 percent water and about 2 percent dissolved salts and nitrogenous wastes, such as urea and uric acid. Excretion by sweating is at most a secondary function to temperature regulation.
- Absorption: Skin absorption is a term that describes the transport of a substance from the outer surface of the skin into both the deep skin layers and the circulation system. Absorption is used to administer medicine into the body by the use of ointments or adhesive patch, such as the nicotine patch. It is important to note that if the skin is exposed to substances that are deemed a risk, then various methods to reduce absorption (such as protective clothing) can be undertaken.
- Water resistance: The skin acts as a water barrier by using a thin layer of lipids (fat) found between the outermost layers of skin cells. These lipids have a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails, and are arranged in a bilayer (two-layered sheet). This uniquely structured fatty layer prevents any water from getting past in either direction – except where the skin layer is modified to form pores.