11.a.the skin and its appendages


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11.a.the skin and its appendages

  1. 1. The Skin and its Appendages
  2. 2. SKIN The skin is derived from three diverse component: 1. Surface Ectoderm:  The epidermis is derives from the surface ectoderm. From single layer ectodermal cells proliferate to give rise to typical stratified squamouse epithelium. The superficial layer sheds off and get mixed with secretions of sebaceous glands to form a whitish sticky substance called vernix caseosa, which acts as a protective covering for newborn infant. Vernix caseosa is protective in function.
  3. 3.  Epidermal ridges develops between 3rd and 5th months of fetal age, this led to formation of characteristics pattern on the tips of fingers and toes. These patterns are genetically determined and are different for each person.
  4. 4. 2. i.  Neural crest Melanoblasts (dendritic cells) These are the cells of epidermis derived from the neural crest cell. The cells synthesize melanin pigments responsible for skin and hair colour.
  5. 5. Cells of Merkel  Appears in epidermis between 8th and 12th weeks of intrauterine life.  They are associated with the sense of light touch discrimination of shapes and textures. iii. Cells of Langerhans  They are developed in bone marrow.  In skin infection, the local Langerhans cells take up and process microbial antigen to become fully functional antigen presenting cells. ii.
  6. 6. 3. The dermis  The dermis is formed by condensation and differentiation of mesenchyme underlying the surface ectoderm This mesenchyme is believed to be derived from the dermatome of somite. Recently it has been held as follows: a.Only the dermis on the dorsal aspect of the head and the trunk arises from dermatomes. b.The dermis of the limbs and that on the lateral and ventral aspect of the trunk arises from the lateral plate mesoderm. c.The dermis over most of the head and over the anterior aspect of neck is derived from neural crest.
  7. 7. Stages in development of epidermsi 1. 2. 3. 4. The line of junction between dermis and epidermis is at first straight. Subsequently, the epidermis shows regularly spaced thickenings that project into the dermis. The portion of dermis intervening between these projections form the dermal papillae. Still later, surface elevations (epidermal ridges) are formed by further thickening of the epidermis in the same situation.
  8. 8. NAILS The nails develops from surface ectoderm.  The ectoderm at the tip of each digits becomes thickened to form a primary nail field.  Subsequently this thickening migrates from the tip of the digit onto its dorsal aspect.  The cells in the most proximal part of the nail field proliferate to form the root of nail.  Here the cells of the germinal layer multiply to form a thick layer of cells called the germinal matrix.  As the cells multiply they are transformed into the nail substance which corresponds to the stratum lucidum of the skin. 
  9. 9. HAIRS  They are also derived from surface ectoderm.  At the site where a hair follicle is to form, the germinal layer of the epidermis proliferates to form a cylindrical mass that grows down into dermis.  The lower end of this downgrowth becomes expanded and is invaginated by a condensation of mesoderm, which forms a papilla.  The hair itself is formed by proliferation of germinal cells overlying the papilla.  As the hair grows to the surface, the cells forming the wall of the downgrowth surrounds it and form the epithelial root sheath.  In addition dermal root sheath is formed from the surrounding mesenchymal cells.
  10. 10. Sebaceous glands A sebaceous gland is formed as a bud arising from ectodermal cells forming the wall of hair follicle.
  11. 11. Sweat glands A sweat gland develops as a outgrowth from the epidermis.  The outgrowth is at first solid but is later canalized.  The lower end of the outgrowth becomes coiled and forms the secretory part of gland.
  12. 12. Anomalies of Akin and its Appendages 1.  Albinism Absence of pigment in skin, hair and eyes occurs because melanocytes are unable to synthesize melanin.
  13. 13. 2. Aplasia The skin may fail to develop in certain regions.
  14. 14. 3. Dysplasia The skin may be in abnormal structure.
  15. 15. Anonychia  Nails maybe absent. Occasionally they may show over development.
  16. 16. Congenital alopecia- hairs may be absent over the scalp Atrichia- absence of hairs in any body part. Hypertrichosis- overgrowth of hairs. 1 2 3
  17. 17. THANK YOU..!!!