Added: 12/02/2005 |
What do you know about skin layers?No doubt, skin is the largest body organ. As it is known in dermatology this organ belongs to the integumentary system including other derivatives such as nails, hairs, oil glands and sweat. Skin is a layer of tissues, which is aimed at protecting all the underlying organs and muscles. It plays one of the most important roles in protecting human body against different pathogens.
Another main function of skin is temperature regulation, regulation, insulation and synthesis of vitamins D and B. Thus, skin protects us from variable external factors, for example chemicals, bacteria, temperature. Skin specific secretions kill these bacteria. A special pigment melanin provides a chemical defense from ultraviolet light which can damage skin cells and may cause cancer.
There are different classifications of skin layers used in medical and dermatological practice. As a rule, medical experts indicate the existence of two main skin layers: epidermis and dermis. Among other skin layers we know hypodermis consisting largely of adipose tissue (fatty layer). Hypodermis is not usually classified as of one of the skin layers.
Speaking about the first and important skin layer - epidermis - it's impossible not to mention that this is the top layer. Due to being a translucent skin layer it allows light to pass through. Epidermis is made up of squamous epithelium. It doesn't contain any blood vessels. It's interesting to admit that epidermis gets all the necessary oxygen and nutrients from other skin layers (the deeper ones). Thus, epidermis is nourished diffusion from the underlying skin layers.
It's a common knowledge skin layers are made up of different cells. As for epidermis, the main type of its cells is keratinocytes containing Langerhans cells and melanocytes. Thus, epidermis is the surface keratinized skin layer. It is divided into several sub layers (so-called "strata"): stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum germinativum. In every of the mentioned epidermis sub layers different cells are formed through so-called mitosis (the process when one cell separates its genome into two identical halves) at the innermost layers.
Beneath the epidermis there's another skin layer called dermis. Both the words epidermis and dermis come from the word "derma" used by ancient Greeks for identifying the skin. Dermis is tightly connected with the top layer by a basement membrane. Just like epidermis, it contains a lot of nerves providing the human the sense of touch, heat, etc. But the distinguishing feature of dermis is that it also contains blood vessels, sweat glands and hair roots.
Dermis is known to be structurally divided into two areas. The first one is a superficial area which is adjacent to the epidermis. It is called the "papillary region". And the second one is deep thicker area or the "reticular region" which lying deep in the papillary region. The reticular region of dermis has such name due to concentration of elastic, collagenous and reticular fibers inside. The mentioned fibers give this skin layer such properties as extensibility, elasticity and strength.
The layer of fat, lying under the dermis, is known as fatty layer or hypodermis. It's depth may be different depending on the person and his/her physiology peculiarities. Hypodermis is made up of clumps of adipose cells (or fat-filled cells) and contains larger blood vessels and nerves.
Thus, skin layers have different structure and contain variable specific cells which give them specific properties and carry out some outstanding functions.
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