Module 4: Skin Physiology - What Is The Skin?

WHAT IS THE SKIN?

The skin is an interface between the individual and numerous different environments, physical, chemical and psychosocial. It is a living, constantly adapting and self-regenerating structure that has developed to function effectively at an air-liquid interface after birth.

Skin-environment interactions are crucial to understanding occupational skin disease.

Although the skin is the largest organ of the body and without a skin one would not survive, little attention is paid to the physiology of skin in undergraduate curricula and cursory attention given to the consequences of skin failure in the clinical years.

The three main functions of the skin are its role in homeostasis, communication and, most importantly for occupational skin disease, its barrier function.

Perhaps the best taught is the role of the skin in homeostasis. The skin is crucial for body temperature control. The many vascular shunts in the skin allow for increased or decreased blood flow to the skin surface and subsequent increased or decreased heat loss to the environment. Sweating is a vital factor in maintaining the core temperature within a narrow range of 37 ± 0.5 ºC as water evaporation from the surface of the skin cools the individual. Being the largest organ in the body and endowed with a vast network of blood vessels, the skin has an important role in haemodynamic homeostasis because large volumes of blood can be shunted from the skin to other areas when needed. An often forgotten homeostatic function of the skin is its metabolic role. It is vital for the synthesis of essential nutrients such as vitamin D and the metabolism of many products including drugs and toxins.

The barrier function of the skin is designed to maintain the high water content of the body while at the same time protect against exposure to many noxious environmental agents. The skin acts as a barrier to a multitude of infectious agents, the damaging effects of radiation and a large range of daily mechanical insults, such as, pressure, shear forces, vibration and extremes of temperature.

All of these functions will be discussed in more detail in the frames that follow.

The skin is essential for communication. The skin communicates information on whom one is and this has significant psychosocial implications for the individual. The skin also provides information on one’s environment and one’s relationship to it. The skin is endowed with many especially adapted nerve endings acting as transducers for the detection of the physical, mechanical and chemical insults referred to above. This information is then transmitted via a rich network of nerves to the central nervous system for processing.