الفهرس 
Histology of Normal Human SkinOnly 14 pages are availabe for public view
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Abstract
Human skin, like all other organs, undergoes chronological aging or intrinsic aging. In addition, unlike other organs, skin is in direct contact with the environment, and therefore undergoes aging as a consequence of environmental damage i.e. extrinsic aging.
Intrinsic aging, also known as the natural aging process, is the slow irreversible degeneration of tissues, which affect almost all body organs. It usually begins in mid 20s and is a continuous process. It is genetically programmed and causes structural and functional changes in all layers of the skin. Although it begins in the mid 20’s, the signs of intrinsic aging are not usually visible for decades.
Extrinsic aging develops due to several factors; ionizing radiation, severe physical and psychological stress, alcohol intake, poor nutrition, overeating, environmental pollution, smoking and exposure to UV radiation. Among all these environmental factors, UV radiation contributes up to 80%. Thus, it is the most important factor in skin extrinsic aging; photoaging.
Basement membrane plays an important roles in maintaining a healthy epidermis and dermis, and repeated damage destabilizes the skin and accelerates the aging process.
The laminins are a secreted family of heterotrimeric molecules essential for basement membrane formation, structure, and function. It is now well established that the laminins play an important role in mediating epidermal-dermal integrity and are essential for the skin to withstand mechanical stresses.
MMPs play an important role in the degradation of BM and in the induction of BM structural damage, including detachment of the BM from basal keratinocytes and disruption of the lamina densa and it is also believed to be responsible for collagen damage in photoaging.
This study was carried to detect the changes in human skin BM in sun exposed skin compaired with those of sun protected skin.
Two skin biopsies were taken from sun-exposed and sun-protected skin of 10 male subjects aged between 50-60 years with skin type III for evaluation of histological changes and ultra structural changes of the BM as well as immuno-histochemistry for laminin and MMP-1.
The histological study using PAS stain for the BM and the electron microscopic study of sun exposed skin revealed that the BM was destructed. The collagenous fibrils of the underlying connective tissue were discrete in comparison with sun protected skin which revealed that the basal lamina was continuous. The collagenous fibrils of the underlying connective tissue were abundant and compact.
Immunoreactivity for laminin was decreased while that for MMP was markedly increased in sun exposed skin and there was positive immunoreactivity for laminin in the basement membrane