Skin Ram Mukkamala

Skin Largest organ completely covering the body continuous with membranes lining body orifices. Average thickness:1-2mm,0.5mm on eyelids & 6mm on palms & soles. pH-4 to 5.6 Renewal of skin takes place in days by shedding of outer layer

Skin

Epidermis

Stratum Corneum: layers of dead cells mechanical protection and water proof. Thickening of corneal layer – Ichthyoses Stratum Lucidum: flat epithelial cells, homogenous translucent appearance Stratum Granulosum: 2-5 layers of flattened rhomboid cells; thinned or absent in Psoriasis Stratum Spinosum: spinous or prickle-cell layer Stratum basale: Usually one cell thick, 2-3 cell thick in glabrous skin and hyperproliferative epidermis

Epidermis Melanocytes: large cells interspersed in basal layer Langerhans cells: Antigen presenting cells Merkel Cells: Nerve endings within epidermis Other structures: Hair, sebaceous glands and ducts of sweat glands

Dermis Connective tissue layer made up of dense & stout collagen fibres, fibroblasts and histocytes. Collagen fibres have elastic property and capable of storing water. 2 layers in Dermis Superficial papillary layer : Projects into epidermis, Contain blood vessels, lymphatic, and nerve fibres. Has some pigment containing cells called CHROMATOPHORE. The papilla are surrounded by rete ridges extending from the epidermis.

Dermis Reticular layer : Made up of reticular and elastic fibres. These fibres are found around the hair bulbs, sweat glands and sebaceous glands. This layer also contain mast cells, nerve endings, lymphatics, epidermal appendages and fibroblasts. The hair follicles with hairs, nails, sweat glands and sebaceous glands, even mammary glands are considered as appendages of the skin. Below the Dermis – subcutaneous tissue helps in temperature regulation

Glands of Skin Sebaceous glands: These are simple or branched alveolar glands situated in the dermis of skin. Structure- Ovoid or spherical in shape, developed from hair follicles and covered by connective tissue capsule. Secrete Sebum which is formed by liquefaction of the alveolar cells. Sweat glands : There are 2 types of glands: Eccrine glands : Distributed throughout the body with exterior opening through sweat pore. Temperature regulation. Apocrine glands : limited to areas like axilla, pubis, areola & umbilicus with opening into hair follicle having thick & milky secretion. It starts functioning only in puberty and had no role in temp. Regulation. It’s secretion increases only in emotional conditions under hormonal control. Have nerve supply by sympathetic adrenergic fibres.

Function Protective – physical and against UV rays Sensory Synthesis of Vitamin D Temperature regulation

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