Anatomy And Physiology

What is Skin



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"What is Skin"
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Our skin and its ancillary structures - certain glands, hair, and nails - make up the largest organ system of the human body, known as the Integumentary System. Skin is arranged in several layers and connected by the hypodermis, or subcutaneous tissue, to underlying structures such bone and muscle. And it serves a critical role in our survival.

There are numerous layers of skin. The deepest layer is a tough network of connective tissue called the dermis which overlies the hyperdermis. This layer consists mostly of fibrous connective tissue and is primarily responsible for the skin's overall strength.

The dermis is further divided into two sub layers: the more superficial papillary layer which is rich in blood supply and the deeper reticular layer, which is avascular (no blood supply), more fibrous in nature, and connects directly to the underlying structures of the hypodermis. The reticular layer depends upon the overlying papillary blood vessels to "feed" it nutrients through a process known as diffusion.

A sheet of tissue separates the dermis from the layers on top of it - the epidermis - which is composed mostly of keratin, a protein mixture that gives the epidermis its characteristic strength and permeability. Also housed within the epidermis are the cells that are responsible for skin color (melanocytes) and the Langerhans cells which play a significant role in our immune response system.

The epidermis itself is made up of numerous layers, the uppermost layers which are dead cells. Only within the deepest layer of the epidermis (the stratum basale) are new cells formed. The stratum basale
is responsible for producing the cells of the basement membrane upon which the entire epidermis sits. As they mature, these cells rise to the surface (are keratinized) and are eventually sloughed off, only to be replaced by the layer below it.

Atop the stratum basale lies yet another layer of epithelium, the stratum spinosum, which is a flattened version of the cells pushed up from the stratum basale. There can be up to 10 layers of these types of cells.
Here, very little cell formation occurs. And as the cells are pushed further and further up to the surface, less and less cell mitosis takes place with no new cell formation occurring superficially to these layers.
Taken collectively, the stratum basale and the stratum spinosum are often referred to as the stratum germinativum since some cell division occurs in these two layers.

The stratum granulosum composes the next 2-5 layers of epithelial cells. Here, the cells begin to flatten out and become diamond-shaped. As they proceed upward to the most superficial layer of the stratum, they degenerate and die. And by the time they reach the next layers of the epithelium - the stratum lucidum and the stratum corneum - all the cells are dead.

The entire process from cell production through the final sloughing of the uppermost epithelial cells takes approximately a period of seven weeks. This ongoing process is of critical importance to our health and well being. Our skin is the barrier that nature has formed to protect us from outside harm. It is our armor, our shield against bacteria and viruses.

Our health really is skin deep. For our skin is not only our source of beauty and protection from harmful intruders, it is a regulator of body temperature, synthesizer of Vitamin D, preceptor of our senses, and an eliminator of our wastes. It is, undoubtedly, not only one of the largest organ systems within our body, but one of the most important. And, it deserves our utmost attention.

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