Non-Specific Defenses

• Physical and chemical defences.

  • The first line of defence against infection is the skin.

  • Epithelial cells form a physical barrier against infection

  – Closely-packed epithelial cells are found in the skin and inner linings of the digestive and respiratory systems.
• Chemical secretions are produced against invading pathogens. Secretions include tears, saliva, mucus and stomach acid.
• Epithelial cells produce secretions such as enzymes, hormones and lubricating fluids that can defend against infection.
• Mucus traps dirt and microbes, preventing them from entering the blood.
• Various glands produce antimicrobial secretions that help kill microbes.
• Other defences

  • Tiny hairs at the entrance to the nose.

  • Cough and sneeze reflexes.

  • ‘Friendly’ bacteria.
• The Inflammatory response -

  • The body responds to a cut or an invasion by a microorganism with a

  localised defence mechanism known as the inflammatory response.

  • Mast cells in the connective tissue become activated and release

  large quantities of histamine.

  • Release of histamine by mast cells causes vasodilation and increased

  capillary permeability.

  • The increased blood flow results in the accumulation of phagocytes

  and clotting elements to the site of infection.