The integumentary system consists of the skin and annexes or appendages. The skin is the largest organ in the body and is a tough, flexible sheath, whose epithelial lining is continuous with those of the respiratory, digestive and genito-urinary, at its outer holes.
The main roles are:
1 .- Protection. The skin prevents the entry of pathogens to be semi-permeable to waterand drugs for external use.
2. - Thermal regulation. Helps maintain body temperature.
3. - Excretion. Is done through sweat.
4. - Synthesis. The skin synthesizes vitamin D and melanin
5. - Sensory Discrimination. Because the skin has receptors for touch, pressure, heat, cold and pain, the individual maintains information on the environment that surrounds it. The appendages, such structuresalso contribute to skin functions mentioned above. Other structures are: hair, nails and sweat and sebaceous glands.
Histological structure of the SKIN
The skin is composed of two layers having different structure and origin: epidermis and dermis are closely related.
The skin thickness is variable, of 0.5-4 mm. or more and "rests" on a loose connective tissue also varies from type to loose fat.This tissue is called the hypodermis and is not part of the skin.
As shown in the epidermis is the most superficial skin and consists of a plane stratified keratinized epithelial tissue, where you can see several layers or strata, depending on their degree of development permit classification of the skin in thick and thin.
The skin is thicker on the palms of the hands and feet TAS planand is characterized by a thick layer of keratin and have a layer called lucid does not exist in thin skin. The thin skin also has keratin, but in it the thickness of the keratin layer is much smaller.
The naked eye observation of the skin to appreciate the presence of grooves and elevations are due to the arrangement of the papillae in the underlying dermis.
These folds are mostvisible in the palms of the hands and fingers, and are fingerprinted.
At M / O the epidermis has five layers thick skin or from deep layers to the surface are: basal, spinous, granular, lucid, and corneum.
Basal layer. Called also germinative layer consists of a cylindrical cell mitotic figures often presented. The basal cells have a nucleus in interphase large and oval, and relatively littlecytoplasm. The cell axis, as well as nuclear, are arranged perpendicular to the basement membrane where they rest these cells.
The basement membrane is indistinguishable in ordinary preparations stained with H / E, but can be seen in preparations stained with PAS and the M / E.
Among the basal layer cells can be observed two cell types: melanocytes, melanin-producing cells and Langerhans cells, whichtoday are known to epidermal macrophages.
Stratum spinosum. Named because their thin cytoplasmic cells show that give the appearance of thorns and the extensions of a link with other cells. This layer is formed by several rows of polyhedral cells, which are flattened as they approach the surface. At M / E has been shown that these intercellular spines are formed by the presence of desmosomesbetween neighboring cells.
Stratum granulosum. It has variable thickness and large flattened cells, named because of the large granular content it presents. Keratohyalin granules are intensely basophilic precursors of soft keratin. This layer is where the epidermal cells die.
Stratum lucidum. This layer is not easy to see and when it does appear as a clear, bright line, above the stratumgranulosum. This layer is composed of several layers of cells showing nuclei inaccurate. In their cytoplasm there eleidina, a substance that comes from the transformation of keratohyalin.
Stratum corneum. It consists of a series of amorphous-like cells, flat and acidophilic. These are dead cells, where the cytoplasm is filled with keratin. The most superficial cells are shed easily.