Epidermis

Epidermis

1. Consists mainly of squamous keratinized epithelium, also: Melanocytes; Langerhans cells and Merkel's cells.

2. consists of 5 layers of keratin producing cells

3. 1. Stratum Basale-

   • have keratin filaments
   • Filaments has role in maintaining cohesion among the cells and in resisting the effects of abrasion.
   • number of filaments increase as they move upwards
   • characterized my intense mitotic activity and is responsible for constant renewal of epidermal cells.
   • 2 layers = Malpighian layer

4. 2. Stratum spinosum

   • spine-studded appearance
   • Filaments NB role in maintaining cohesion among the cells and in resisting the effects of abrasion
   • Area exposed to more friction = thicker stratum spinosum
     • Psoriasis = increase in number of proliferating cells and decrease in cycle time of these cells, Greater epidermal thickness and more rapid renewal of epidermis
   • cytoplasm displays membrane coating granules=lamellar bodies (lamellar disks) formed by lipid bilayers

5. 3. Stratum Granulosum

   • Granules not surrounded by membranes
   • Granules contain:
     • - Profilaggrin
       • - Involucrin
         • - Small-proline rich protein
           • - Loricrin
   • Lamellar bodies increase in size
   • Granules discharge contents into ICS-deposited in form of sheets containing lipid
     • Function: acts as water barrier as a barrier to penetration of foreign materials

6. 4. Stratum lucidum

   • Thick skin &stranslucent
   • no organelles and nucleus
   • Desmosomes still evident between adjacent cells.

7. 5. Stratum Corneum

   • contains keratin and amorfous proteins (thick plasma membrane =horny cells
   • cells are continuously shed at the surface of this layer