stratum cor´neum the outer horny layer of the epidermis, consisting of cells that are dead and desquamating. The basement membrane zone is better demonstrated with periodic acid-Schiff (PAS) stain. However, c-fos and c-jun (components of AP-1 or Activator Protein 1) can be reactivated in cultured fibroblasts from old donors (33), an indication that it is biologically possible to reactivate genes that are down-regulated in aging. Metaplasia occurs when the mature cells in a tissue change into a form that is not normal for that tissue. The stratum basale (also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis. Gopinathan K. Menon, ... Robert Kalafsky, in Skin Aging Handbook, 2009. The deepest/innermost layer of the epidermis is the stratum basale. The stratum basale (also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis. It is usually only in this layer that cells divide. It occurs following loss of cohesion between epidermal keratinocytes or between epidermis and dermis, resulting in the formation of a fluid-filled cavity. Stratum lucidum (clear cell layer): This layer is composed of nonnucleated keratinized cells and is only present in hairless areas of the body. The epidermis is the topmost layer of skin that can touch, see and feel. Hence, a whole slew of new ingredients, such as cococin, thiodipropionic acid (49), endothelin antagonists (which block keratinocyte-melanocyte interaction for increased pigment production and transfer to epidermis), protease inhibitors from soy (50), peptides, melanocyte stimulating hormone antagonists, and small interference RNAs that silence the messenger RNA for tyrosinase (51) have appeared in the cosmetic field. As the newly formed TJs mature, the existing TJs disappear over time (Fig. Transepidermal elimination is a mechanism by which foreign or altered constituents can be removed from the dermis. Pustules that are filled with isolated rounded keratinocytes with a normal nucleus are referred to as acantholytic pustules. The basal cell layer (stratum basale, or stratum germinosum), is a single layer of cells, closest to the dermis. Epidermal dysplasia is characterized by keratinocytes that are atypical in size, shape, and staining characteristics, and whose polarity has been disrupted (Fig. Products aimed at boosting the skin's immune function are claimed in a few anti-aging products but, by and large, the immunocompetence of skin is not a widely addressed facet of anti-aging cosmetics. Provides skin both strength and flexibility Stratum basale The stratum corneum functions to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress. The cells in the stratum basale bond to the dermis via intertwining collagen fibers, referred to as the basement membrane. Vesicles that are located between the SB and the underlying mesenchyme are termed clefts. Stratum granulosum (granular cell layer): The cells in this layer are in the process of dying, with nuclei that are shrinking and undergoing chromatolysis. Skin that has four layers of cells is referred to as “thin skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. The epidermis has no blood supply and it is nourished by diffused oxygen from surrounding air. These changes are, in part, what give the strata their unique characteristics. One of the most visible signs of photoaging is pigmentary changes, such as focal hyper-pigmentation or uneven pigmentation of the facial skin. These cells are constantly dividing and pushing already-formed cells towards the skin's surface. The stratum corneum is the outermost layer of the epidermis, and is made up of 10 to 30 thin layers of continually shedding, dead keratinocytes. stratum basa´le the deepest layer of the epidermis, composed of a single layer of basophilic cells. 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