Structure and function of skin

Structure and function of skin

The skin is composed of three layers epidermis dermis and subcutaneous tissue


Which is the outer layer of the skin it is composed of three basic cell types keratinocytes ,melanocytes ,and langerhans cells the keratinocytes or squamous cell is the principal cell of the epidermis the epidermis is divided into four main layers
beginning with the innermost layer 1- basal cell layer (stratum germinativum_2- squamous cell layer (prickle cell layer or stratum spinosum) 3- granular cell layer (stratum granulosum) 4- horny cell layer (stratum corneum) the melanocyte is the dendritic pigment producing cell of the epidermis and found in the basal layer the langerhans cell is a dendritic cell present in the malpighian layer functionally it is of the monocyte -macrophage lineage and originates in bone marrow which it is play a role in some immunological reactions and defense agonist parasitic infection epidermal appendages include hair nails sebaceous glands and sweat glands


Which is bounded externally by it is junction with the epidermis and internally by subcutaneous fat contributes to 15 -20 %of total body weight of the human body it largely consists of a supporting matrix or ground substance and connective tissue formed mainly of collagen and elastin the prodominant cellular elements in the dermis are fibroblast the dermis also contains blood vessels lymphatics as well as peripheral sensory and motor nerve endings the dermo-epidermal junction the junction of epidermis and dermis is formed by the basement membrane zone which is considered to be a semipermeable filter that permits exchange of cells and fluid between the epidermis and dermis it also serves as a structural support for the epidermis and holds the epidermis and dermis together the epidermis and dermis interdigitate through downwards

projections of the epidermis (rete pegs) and upwards projections of the dermis (papillae

 Subcutaneous tissue

Beneath the dermis lies the subcutaneous tissue which is composed of lobules of fat cells separated by fibrous septa and large blood vessels

Function of the skin

As follow 1- the skin acts as a two way barrier to prevent the inward or outward passage of water and electrolytes 2- the intact stratum corneum prevents invasion of the skin by normal skin flora or pathogenic microorgansims 3- melanin pigment protects the skin from the harmful effects of ultraviolet radiation 4- the skin plays a major role in thermoregulation of the human body heat can be lost through the skin surface by radiation convection conduction and evaporation of sweat 5- the skin protect against mechanical injury 6- the skin plays an important role in the immunological host defense 7- nerves in the skin are responsible for the sensation of touch pain warmth cold and itch 7- the skin also has endocrinal function as vit b and has medicolegal  function


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