The Human Skin - Function and Ageing

Published: 16th March 2011
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The human skin is an important organ system for protection of the body against external entities. Understanding its structural components, and functions is important while we take care of this organ in our day to day life. Not suprisingly, it is one of the most taken care of organs of our body.

Functions of the skin:
The skin performs a number of functions for the human body which are:
1. Protection- The skin is the outermost layer of the body and provides a barrier to environmental stresses such as climatic change, toxins, chemicals, and microorganisms.
2. Sensing- With pressure sensing and heat sensing neurons, the skin acts as useful sensing organ and provides one of the five senses in the human body - touch.
3. Storage- The skin provides a location to store fat and nutrients.
4. Water Resistance- The skin acts as a hydrophobic barrier and prevents water from entering freely into the body from outside, thereby maintaining the structural integrity of the body and also preventing water from inside going outside. The water can be released in the form of sweat in a controlled manner.

Layers of the Skin:
Human skin is composed of 2 primary layers:
1. The dermis- which is the deeper layer
2. The epidermis- which is the more superficial layer of the skin and provides most of the barrier function.

Components of the Epidermis:
The epidermis which is the superficial layer of the skin provides most of the protection to the underlying layers of skin and the underlying organs as well. It is composed of 4 principle types of cells:
1. Keratinocytes - which provide protection to other cells by producing a strong protein keratin.
2. Melanocytes - which also provides protection to cells beneath them by producing a dark pigment - melanin. This melanin prevents harmful ultraviolet light from reaching to the lower layers of skin and causing damage. It is a well known fact that over exposure to ultraviolet rays of the sun cause skin cancer (this is when the melanin produced can no longer protect the skin). The melanin is also responsible for the color imparted to the skin.
3. Merkel cells - help in sensory functions of the skin
4. Langerhans cells - help in the immune system of the skin

The epidermis can also be divided into 5 sub-layers:
1. Stratum Corneum
2. Stratum Granulosum
3. Stratum Spinosum
4. Stratum Lucidum
5. Stratum Germinativum

Components of the Dermis:
The dermis is the underlying layer of the skin and provides more of the regenerating properties of the skin and imparts skin with structure. The primary cellular components of the dermis include:
1. Fibroblasts- These are found in other tissues as well as the skin. They provide structure to the skin and are also involved in healing the skin upon getting wounds.
2. Adipocytes- These cells provide nourishment and are the storage sites for fat or adipose tissue.
3. Macrophages- macrophages are cells found all over the body. These cells are a part of the immune system and participate in phagocytosis of pathogens.

According to an article The Ageing Skin- Structure of skin, the main cause of skin ageing is not the loss of any of the cells mention about but the loss of other dermal matrix components. The dermis also contains matrix components such as collagen, elastin, and glycosaminoglycans. These proteins and polysaccharides provide the skin with structural rigidity, balanced with elasticity and also keeping the skin supple and full by retaining water.

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