Exudation of fluid

Functions of Exudate

1. Dilutes the toxic agent, reducing its effect upon the tissue cells.
2. The protein components may contain antibodies which attack or coat (opsonise) the irritant.
   • This makes the irritant more digestible to neutrophils and macrophages.
3. Exudates may contain fibrin.
   • This is very sticky - immobilises the irritant.
   • Provides a framework over which the leukocytes crawl to reach the irritant.
   • Fibrin is also chemotactic to neutrophils, bringing more of these cells into the injured area.
4. Exudate on a suface will wash away the irritant.
   • E.g the skin and alimentary track.
5. Brings the irritant to the lymph nodes, via the lymphatics, for further processing or antigen presentation.
   • Preferably within white blood cells such as macrophages and neutrophils.
   • Local lymph nodes may also be inflamed following inflammation of a tissue which drains into them.

Sequelae to Exudation

• Catarrhal and serous exudationresolve when the irritant is overcome.
  • Alternatively, they may progress to a more serious reaction.
• Fibrinous exudates may also resolve if the fibrin is digested by macrophages.
  • In the pleural and peritoneal cavities, the fibrin may become organised into fibrous tissue, producing adhesions between the visceral surface.
• Diphtheritic inflammation will only repair by scar formation.
• If haemorrhagic lesions are widespread, they most commonly associated with acute deaths.
  • For example in acute viral, bacterial or toxic diseases.
• If the exudation is strictly localised, for example in brusing, then repair may occur.
• The resolution of abscesses depends upon their location.
  • If the abscess is near to a surface it will rupture onto it.
  • This is beneficial in the skin where it discharges to the exterior, hopefully getting rid of the pyogenic organism.
  • If the abscess is in deeper tissues, there is extensive fibrous capsule formation.
    • The fluid becomes inspissated due to withdrawal of water content.
    • Macrophages digest the necrotic remains.
    • Fibrous tissue organises the interior.
    • The very end result is a fibrous scar.