|
|
|
Crystals:
Crystals deposited in tissues can be from exogenous
or endogenous sources. Endogenous products that can deposit as crystals
in tissue include haemoglobin, uric acid and cholesterol. Exogenous products
that can deposit as crystals in tissues include oxalates, silicates and
pharmachological agents eg sulphonamides.
The accumulation of crystalline haemoglobin
is most often seen in the context of acute severe haemolysis with haemoglobin
crystals depositing in renal tubules.
Cholesterol is a component of cell membranes
and also an important constituent of body lipid stores. Cholesterol accumulates
in tissues as crystals, but these are dissolved in routine processing
leaving needle-like spaces, “clefts” behind.
Cholesterol crystal formation is common in:
-
Areas of fat necrosis
-
Fatty atheromatous plaques in major blood vessels
-
Areas of haemorrhage
-
Fatty tumours
Deposits of uric acid crystals and urates are termed
"gout" which is a disease of purine metabolism. It
is seen most commonly in bids, snakes and humans and is due to excessive
production or insufficient excretion of uric acid. Chalky white masses
of uric acid (termed "tophi") develop in tissue and
cause local inflammatory reactions.
Crystals of calcium oxalate are deposited in
tissues in toxic disease, casusing increased oxalic acid in blood and
urine. Causal agents are most often plants that contain large amounts
of oxalic acid, or ethylene glycol (antifreeze)
Desert atmospheres are rich in silicate dusts,
and animals that roam these areas commonly have crystal-laden macrophages
in peribronchiolar tissue in their lungs. The deposits are complex silicates
and aluminium-potassium silicate. These lesion are especially common in
animals that root about in the ground. In clinical disease resulting from
silicates, animals usually have multiple granulomas in the lungs, composed
of large foamy macrophages.
Nephrosis and uraemia may result from ingestion of large
doses of sulphonamides, particulalry if associated with inadequate
water inatke. These disorders are likely to occur in animals that are
febrile and dehydrated. Sulphonamide crystals are often visible grossly
in the renal pelvis and as pale, yellowish radial lines in the renal medulla.
 
|
