General Veterinary Pathology

EXOGENOUS PIGMENTS - 1

Colouring agents

Colouring agents are called as pigments. Tissues may be discoloured (e.g. Jaundice, tattoo) or excessively coloured (e.g. Melanosis) in diseases. 

• Origin
• External or exogenous pigments
• Internal or endogenous pigments

Exogenous pigmentations

In exogenous pigmentations colouring substances can enter the body by three different routes.

• Respiratory route by inhalation
• Alimentary route by ingestion
• Cutaneous route by injection

Of these three entries, entry through respiratory route is the most common pathway for exogenous pigmentations. This results in pneumoconiosis characterized by pigmentation and fibrosis. Pneumoconiosis is a general term applied for any permanent deposition of substantial amounts of particulate matter in lung disease by inhalation; Depending upon the type of exogenous pigment, the conditions are termed as follows

• Coal dust-Anthracosis
• Stone dust -Silicosis
• Iron dust -Siderosis
• Cotton dust –Byssinosis
• Asbestos dust -Asbestosis
• Cement - Chalicosis

Anthracosis

• Sources: Air pollution (Near busy high ways- zoo animals and dogs)
• Coal mines (Horses and mules)
  • The carbon particles inhaled are phagocytised by alveolar macrophages and transported through regional tracheobronchial lymph nodes. The carbon particle being inert is not metabolised by the body and hence remains in the tissue permanently.
• Grossly , the lung shows peppered appearance. The carbon deposits in sub-pleural area are seen as black foci. Regional lymph nodes may show carbon deposits in the medulla because of concentration of sinus macrophages in that location.

Anthracosis - Lung

• Microscopically , fine black granules may be found within the macrophages or deposited extracellularly in the lungs (alveolar wall) or around the peribronchial areas. The pigments are resistant to solvents of bleaching agents and non-reactive. The carbon being mildly irritant elicits slight pulmonary fibrosis.  

Silicosis

Silicosis is deposition of silica in the lung. The condition is more common in human beings than in animals as an occupational hazard who are working in mines and quarries. The crystalline form of silica is more harmful irritant than amorphous form. The silica is a powerful irritant and is insoluble in body fluids.

• Grossly , lung shows multiple, small discrete nodules in the parenchyma. Similar lesions may also be found in the regional lymph nodes and pleura. Extensive fibrosis may predispose to pulmonary tuberculosis.
• Microscopically , the nodular regions are formed by concentric layers of hyalinised collagen.