ANATOMY OF THE SKIN
A) Skin histology and terminology :
The skin consists of 2 main layers ,the epidermis and the dermis. The dermis and the epidermis are derived from a different embryologic tissue type. The subcutaneous tissue resides immediately beneath the two primary layers of skin. The outer layer of skin (the epidermis) consists of stratified squamous keratinizing epithelium and is derived from ectoderm (Fig. 1). The epidermis contains no blood vessel sand is nourished entirely from tissue fluid emanating from the inner (deeper) vascularized skin tissue known as the dermis. The dermis is derived from mesoderm and contains the nutrient- providing blood vessels. Each of the two primary layers of skin has structurally distinct sublayers
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Antimicrobial peptides like β-defensins, which prevent invasion of microbes. ii. Protection from Mechanical Blow : Skin is not tightly placed over the underlying organs or tissues. It is somewhat loose and moves over the underlying subcutaneous tissues. So, the mechanical impact of any blow to the skin is not transmitted to the underlying tissues. iii. Protection from Ultraviolet Rays : Skin protects the body from ultraviolet rays of sunlight. Exposure to sunlight or to any other source of ultraviolet rays increases the production of melanin pigment in skin. Melanin absorbs ultraviolet rays. At the same time, the thickness of stratum corneum increases. This layer of epidermis also absorbs the ultraviolet rays .
2. Sensory function:-Skin is considered as the largest sense organ in the body. It has many nerve endings, which form the specialized cutaneous receptors). These receptors are stimulated by sensations of touch, pain, pressure or temperature sensation and convey these sensations to the brain via afferent nerves. At the brain level, perception of different sensations occurs .
3. Storage function :- Skin stores fat, water, chloride and sugar. It can also store blood by the dilatation of the cutaneous blood