Epidermis, Biology

EPIDERMIS -

  1. Ectodermal in origin. Outer part of skin. Made up of stratified epithelium.
  2. Branches of sensory nerves present. More branches on lips, tips of fingers.
  3. Blood vessels are absent. Get necessary miaterials from dermis.
  4. Porous in nature. Thickest in sole. Thinnest in cornea (conjuctiva).
  5. On palm grooves are known as sulcicutis & ridges are known as cristae cutis. Their study is dactyloscopy.
  6. Their arrangement on fingers & thumb are finger mark, i.e. dermatoglyphics.
  7. After the birth of babies, permanent linings on abdomen of women are linear gravidarum.
  8. In epidermis outer to inner following layers are clear -

1. Stratum corneum

2. Stratum lucidum

3. Stratum granulosum

4. Stratum spinosum

5. Stratum malpighi

 

 

1.      STRATUM CORNEUM -

  1. Outermost part of epidermis. 8-10 layers of cells present.
  2. Cells are flat, intercellular spaces absent, nucleus absent, cytoplasm negligible, more or less dead.
  3. Keratine protein present which is scleroprotein. It gives impermeability to skin.
  4. As on inner side new layer are formed by S. malpighi, outer layer of corneum is shed off. It is known as ecdysis.
  5. Free cholesterol and fat present in this layer.
  6. Claws, nails, horns hoofs in animals are formed by this layer.
  7. This layer is endocrine in nature. Hormon secreted by this layer reduces power of cell division in S. malpighi.
  8. If we remove this layer sensivity is increased.

 

2.      STRATUM LUCIDUM -

  1. Present inside S. corneum. 2-3 layers present. Cells are flat, intercellular spaces absent.
  2. Nucleus present, cytoplasm present, living cells eleidin present, that gives transparnacy to this layer.
  3. It is also known as clear zone, barrier layer.
  4. This layer checks water & other minerals to move out.

 

3.      STRATUM GRANULOSUM -

  1. In cytoplasm keratohyaline present which is made up of polysaccharide, Ca & RNA, basophillic in nature.
  2. Cornification or keratinization is common i.e. keratohyaline is converted first in to eleidin then in keratine.
  3. In this process malpighi cells first become cuboidal then squamous.

 

4.      STRATUM SPINOSUM -

  1. Situated inside S. granulosum. Cells are polygonal. Also known as prickle cells.
  2. Keratohyaline granules present little.

 

5.      STRATUM MALPIGHI -

  1. Also known as S. Germinativum.
  2. Inner most part of epidermis. 1-2 layers present. Capable of cell division.
  3. Cells are round in shape but columner type, so this layer is also known as S. Cylindricum.
  4. Complete epidermis is formed by it.
  5. S. Malpighi rests on basement membrane of dermis.
  6. S. Malpighi forms out growth as Rete pegs enter in dermis.
  7. Melanin pigment present, formed in melanasome part of melanocyte, dopa oxidase enzyme is needed for it.
  8. Colour of skin depends on quantity and shades of melanin.
  9. Melanin absent in palm & sole. Melanin maximum in areola mammary.
  10. Worm blooded animals of hot & humid area have abundent melanin pig. It is explained by Gloger's law.
  11. Melanin is under control of MSH & UV rays.
  12. Darking of skin after exposure to UV rays is common.
  13. In man complete absence of melanin is albinism due to recessive gene & absence of tyrosinase as melanin is derivative of tyrosine.
  14. Chromatophores absent. In frog present in dermis.
  15. In leucodermea melanin becomes absent at patches. Such skin is peibled skin.

158_mammalian skin.png

Posted Date: 10/1/2012 4:31:58 AM | Location : United States







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