Category:Acute Inflammation

Fluids

Serous

• Serous fluids are formed due to mild vascular injury in an organ or in vessels underlying a

surface.

• The fluid is clear to cloudy fluid.
  • Little protein is present.
• Examples:
  

  Burn injury. (Courtesy of T. Scase)
  • Vesicles of the skin.
  • Many inflammations in joints.

Catarrhal

• Catarrhal inflammation is a mild form of inflammation.
• Occurs on mucous membranes where there are many mucus cells.
• The consistency of catarrhal exudate varies from water to gelatinous.
• Colour varies from cloudy to pinkish.
• This form of exudation is essentially a shedding of epithelium containing many mucus cells, neutrophils, some RBCs, and flecks of fibrin.
• Common in mild forms of rhinitis, tracheitis, bronchitis, gastritis and enteritis.

Fibrinous

• Fibrinous exudation occurs in more severe endothelial injury.
  • Injury results in the escape of fibrinogen, which is converted to fibrin.
• The fibrin formed appears as a yellowish coagulation on the surface of or within a tissue.
  • Common in the lungs and on serous surfaces.
• In hollow organs the fluid may coagulate to form casts of the lumen.
• Fibrin will peel off from the underlying tissue without causing damage to it.

Diptheritic

• Diphtheritic exudate a more severe form of fibrinous exudate in which there is considerable necrosis of the underlying tissues.
• Diptheritic exudate is firmly adherent to the underlying tissue.
  • Attempts at removal cause tearing of this tissue>
• Commonly seen with internal surface fungal infections.
  • E.g. in the nose of the dog and the guttural pouch of the horse.
  • Fungal toxins penetrate the underlying tissue causing coagulation necrosis.

Haemorrhagic

• This is a severe acute to peracute inflammation in which haemorrhage is the main component.
• Seen in the lymph nodes, lungs and intestine in severe inflammation.

Purulent

• In purulent inflammation, pus is the predominant feature.
  • Pus is an admixture of dead and dying neutrophils with necrotic cells and a pyogenic agent.
    • Proteolytic enzymes released by the dying neutrophils lyse tissue cells to produce a fluid.
• Colour varies depending upon the agent.
  • May be white, yellow, green or brown.
• An abscess is a circumscribed sphere of pus surrounded by a pyogenic membrane.
  • The pyogenic membrane is composed of capillaries bringing neutrophils into the sphere.
  • This rapidly becomes enveloped by a fibrous tissue capsule.
    • A local connective tissue response attempting to wall off the purulent irritant from nearby normal tissue.

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 rganised 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.