Surface Barriers


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•  The skin and mucous membranes form a primary defence against pathogens that cause infectious disease

The first line of defence against infectious disease are the surface barriers that prevent the entry of pathogens into the body

  • These surface barriers include both the intact skin and mucous membranes


  • Protects external structures when intact (outer body areas)
  • Consists of a dry, thick and tough region composed predominantly of dead surface cells
  • Contains biochemical defence agents (sebaceous glands secrete chemicals and enzymes which inhibit microbial growth on skin)
  • The skin also secretes lactic acid and fatty acids to lower the pH (skin pH is roughly ~ 5.6 – 6.4 depending on body region)

Mucous Membranes

  • Protects internal structures (i.e. externally accessible cavities and tubes – such as the trachea, oesophagus and urethra)
  • Consists of a thin region of living surface cells that release fluids to wash away pathogens (mucus, saliva, tears, etc.)
  • Contains biochemical defence agents (secretions contain lysozyme which can destroy cell walls and cause cell lysis)
  • Mucous membranes may be ciliated to aid in the removal of pathogens (along with physical actions such as coughing / sneezing)

Overview of Physical and Chemical Surface Barriers

surface barriers