HUMAN SKIN
- the basic facts                   

• what is skin? (Latin - cutis) 
  • is your body's largest organ
  • covers your entire body
  • has a total surface area of ± 1.5 - 2 m² (depending on your body's size)
  • makes up ± 7% of your body's total weight
  • weighs ± 4 kg
  • suffers the most wear and abuse of any part of the human body


• composition of your skin:
  • two (2) distinct main layers: the EPIDERMIS and the DERMIS
  • EPIDERMIS:
    • nature of:
      • the thinner of the two main skin layers
      • made up of many cell layers
      • has no blood vessels of its own
      • the most inner cell layer provides cells for the outer cell layers, by having its cube-shaped cells divide quickly
      • new cells push older cells toward the surface
      • as epidermal cells move toward the surface, they become enriched in keratin (a fiberous protein - also found in hair and nails)
      • upon reaching the surface, these cells have died and become flat
      • at the surface, these dead cells "slough-off"
      • Epidermis is replaced every few weeks
      • in a lifetime the average person will shed ± 18 kg of skin
    • structure of (from surface inward):
      • Stratum Corneum (outer most layer) - horny layer - accounts for up to 75% of the Epidermis' thickness
      • Granular layer (stratum granulosum)
      • Spinous layer (stratum spinosum)
      • Basal layer
  • DERMIS:
    • nature of:
      • the thicker of the two main skin layers
      • is protected by the Epidermis
      • made up of connective tissue - with elastin fibers (to keep it flexible and pliable) and collagen fibers (for strength and resilience)
      • rich in blood vessels and nerve endings
      • feeds the Epidermis with nutrients and oxygen
      • contains the structures of the intergumentary system (hair follicles, oil and sweat glands)