Skin Structure/Function

Four main functions

• Protection – provides a physical barrier against infection/trauma etc
• Sensation – contains the majority of receptors responsible for sensation (touch, pressure, pain and temperature)
• Thermoregulation – insulation, sweating and changes in blood flow to the skin (heat transfer) controls body temperature
• Metabolism – e.g. vitamin D synthesis; triglyceride storage

There are three main layers

• Epidermis
  • Most superficial layer- relatively thin (thickness varies between body sites)
  • Consists of stratified squamous epithelial cells
    • Mainly keratinocytes
      • Become more ‘mature’ as they migrate superficially from the basement membrane- losing their nuclei and becoming keratinised
        • Four ‘layers’ (from superficial to deep)- stratum corneum (‘corneocytes’- dead, dried out, anuclear cells); stratum granulosum (contain basophilic granules); stratum spinosum (intercellular desmosomes give a spindle appearance); stratum basale (columnar cells with regenerative capacity)
    • Melanocytes
      • Found in the basal layer; produce melanin which contributes to skin colour and absorption of UV light
    • Langerhans cells
      • Immune cells- responsible for idenitifying, fragmenting and presenting allergens/foreign material to the lymphatic system and potentially activate the immune system
    • Merkel cells
• Dermis
  • Fibrous connective tissue under the epidermis- consists of mainly collagen and elastin, bound together by ground substance.  Adnexal structures (e.g. hair follicles and sweat glands; nerve endings etc) are found here
• Hypodermis/Subcutis/Subcutaneous layer
  • Contains the adipose tissue immediately under the skin.

A note about skin lines…

• Blaschko’s lines
  • Thought to represent the pattern of epidermal skin cell migration and proliferation during development.  They may be visible in inherited conditions.
• Langer’s lines (wrinkle lines)
  • These outline the arrangement of fibrous tissue in the dermis and hypodermis.  They are primarily longitudinal in the limbs and horizontal in the trunk (with exception of the limb flexors which are also horizontal)
  • They may be important when deciding where to make an incision, as cutting across them may result in increased/uneven tension across the wound and poorer healing.

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