Water and Electrolytes 15 



CALCIUM AND CELLULAR INJURY 



The Deposition of Calcium in Damaged Tissues 

 (Dystrophic Calcification) 



Certain types of tissue damage are commonly associated with 

 the deposition of calcium salts in the affected region. Notable 

 examples are tuberculous lesions showing coagulation necrosis 

 (caseation), necrosis in fat, arteriosclerosis and infarcts (necrosis 

 due to sudden loss of blood supply) . The nature of these calcium 

 deposits appears to be similar to that found in normal bone, i.e., 

 to consist of hydroxy apatite (Cai [Po 4 ] 6 (OH) 2 ) on which is 

 absorbed carbonate, magnesium and sodium ions. 



The mechanism of both normal and dystrophic calcification is 

 very uncertain. In normal calcification several factors have been 

 implicated; a supply of glycogen, the formation of a phosphate 

 ester by the process of glycolysis, the breakdown of this ester by the 

 enzyme alkaline phosphatase with resultant formation of insoluble 

 calcium phosphate, a reaction between the organic matrix (e.g. 

 sulphate and glucuronic acid groups of chondroitin sulphate) of 

 the tissues and calcium ion, with subsequent calcium binding. 



With regard to dystrophic calcification, the early suggestion that 

 fatty acids are formed in necrotic tissue and that these form in- 

 soluble calcium soaps later replaced by calcium phosphate, is no 

 lonser held to be valid. Increased alkalinity of necrotic tissue as a 

 cause of precipitation of acid-soluble calcium salts has also found- 

 ered through lack of evidence. Some sites of abnormal calcification 

 show strong phosphatase activity, e.g. caseous tubercles in rabbits, 

 phosphatase not appearing until necrosis was apparent. This ob- 

 servation suggests that phosphatase activity may be involved in both 

 normal and dystrophic calcification. The enzyme might well be 

 liberated from intracellular sites, e.g. mitochondria after cell death. 

 However, not all types of calcifying degenerate tissue show phos- 

 phatase activity. This type of abnormal calcification may be 

 favoured by the development in degenerate tissues of greatly in- 

 creased calcium binding properties or by the loss of substances that 

 normally serve to keep calcium in a non-ionic but soluble form. 



