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Skin

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Skin

  1. 1. Anatomy and Physiology of SkinDr Ashwini Kalantri
  2. 2. Skin Largest organ of the body Completely covers the body Continuous with membranes lining body orifices Average thickness: 1-2 mm. (0.5mm eyelids, 6mm palms and soles) pH: 4-5.6 Renewal of skin takes place in 28-50 days by shedding of the outer layer.
  3. 3. Structure of SkinLayers 1. Epidermis 2. Dermis
  4. 4. Epidermis Most superficial layer of the skin composed of stratified epithelium No blood vessels Nutrition provided by the capillaries of dermis Approx. thickness 0.4-1.5mm, thickest on palms and soles.
  5. 5. Layers of Epidermis Stratum Corneum { Stratum Lucidum { {Stratum Granulosum Stratum MucosumStratum Germinativm {
  6. 6. Cells in the Epidermis Keratinocytes: Major building block of the epidermis Melanocytes: Large cells interspaced among keratinocytes, produce melanin. Langerhans Cells: Antigen presenting cells Merkel cells: Represent special nerve endings within epidermis Hair, Sebaceous glands and ducts of sweat glands.
  7. 7. Colour of the Skin Pigmentation of skin: Melanocytes contain the pigment melanin which darkens the skin on exposure to sunlight Hemoglobin content in blood: The level of oxygenation of blood and amount of blood circulating in the dermis play an important role in skin colouration.
  8. 8. Dermis Connective tissue layer made up of dense and stout collagen fibers, fibroblasts and histocytes. Collagen fibers have elastic property and are capable of storing water. Layers: 1. Superficial Papillary Layer 2. Reticular Layer
  9. 9. Superficial Papillary Layer Projects in to the epidermis Contains blood vessels, lymphatics and nerve fibers. Has some pigment containing cells called chromatophore. Dermal papillae are finger like projections arising from this layer
  10. 10. Reticular Layer Made up of reticular and elastic fibers These fibers are found around hair bulbs, sweat glands and sebaceous glands. Also contains mast cells, nerve endings, lymphatics, epidermal appendages and fibroblasts. The hair follicles with hairs, sweat glands, sebaceous glands and nails.
  11. 11. Glands of the Skin 1. Sebaceous Glands 2. Sweat Glands
  12. 12. Sebaceous Glands Structure: Ovoid or spherical in shape, developed from hair follicles and covered by connective tissue capsule Secretion: Secrete a oily substance called Sebum. Composition: Contains free fatty acids, sterols, paraffin, waxes, squalene and triglycerides. Functions: FFA has antibacterial and antifungal properties. Lipids keep skin smooth and oily, protecting from unnecessary desquamation and injury.
  13. 13. Sweat Glands - Eccrine Distributed throughout the body with exterior opening through sweat pore with watery and clear discharge. Temperature regulation Secretion increases with increase in temperature and emotions under nervous control Nerve supply by sympathetic cholinergic fibers.
  14. 14. Sweat Glands - Apocrine Distributed only in a limited area – Axilla, pubis, areola and umbilicus. Opens in to the hair follicle having thick and milky secretion. Starts functioning with puberty and has no role in temperature regulation Secretions increase under emotional conditions under hormonal control. Supply by sympathetic adrenergic fibers.
  15. 15. Functions of Skin
  16. 16. Protective Protection from bacteria and toxic substances by secreting lysozyme. Protection from mechanical blow Protection from UV rays with the help of melanin pigment.
  17. 17. Sensory Skin is considered the largest sensory organ Many nerve endings forming a specialized cutaneous receptors.
  18. 18. Storage Stores fat, water, chloride and sugar. Can also store blood with vasodilation of the cutaneous blood vessels
  19. 19. Synthetic Vitamin D3 is synthesized in the skin with the action of UV rays on cholesterol.
  20. 20. Temperature Regulation Excess heat is lost from the body by radiation, conduction, convection and evaporation. Active role in heat loss by secreting sweat. The lipid content of sebum prevents heat loss in cold temperature.
  21. 21. Water and Electrolyte balance Excretion: Waste materials like urea, salts and fatty substances are also excreted. Absorption: skin can absorb fat soluble substances and some ointments. Secretion: Sweat and sebum are secreted by the sweat and sebaceous glands. Helps in temperature and water balance. Sebum helps in keeping the skin smooth and provides protection.

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