Calcification stas in mitochondria Calcification The deposition of mineral salts of calcium is a normal process in the formation of bone and cailage. Calcium entry into dead or dying cells is usual, owing to the inability of such cells to maintain a steep calcium gradient. Pathological calcification Pathological calcification is the abnormal deposition of calcium salts in soft tissue. It is of two types A) Metastatic Metastatic calcification reflects deranged calcium metabolism. Its a change associated with an increased calcium concentration in the serum. In general almost any disorder that increases the serum calcium level can lead to calcification in locations as the alveolar septa of the lung, renal tubules and blood vessels. The fundamental abnormality is the pathological entry of large amount of ionic calcium into the cell organelle, chiefly the mitochondria (it is suggested that mitochondria are the organelles firvt involved in the pathogenesis of metastatic calcification). Sites of metastatic calcification - Basement membrane & tubular lamina of kidney - Alveolar wall of lungs (most common site) - Interstitial tissue of gastric mucosa - Systemic aeries - Pulmonary veins - Cornea & conjunctiva - Synovium of the joint - Tendons These sites are prone to calcification because these tissues loose acid and therefore have alkaline internal environment. Alkaline pH ours precipitation of calcium salts. B) Dystrophic calcification Dystrophic calcification refers to the macroscopic deposition of calcium salts in injured tissues. This type of calcification does not simply reflect an accumulation of calcium derived from the bodies of dead cells, but rather represents an extracellular deposition of calcium from the circulation or interstitial fluid. Denatured proteins in dead or irreversible damaged tissue preferentially bind phosphate ions. Phosphate ions react with calcium ions to form a precipitate or calcium phosphate. Thus necrotic tissue serve as calcium sink. In many locations such as in a case of tuberculous caseous necrosis in the lung or lymph nodes, calcification has no functional consequences. Dystrophic calcification may also occur in crucial locations such as in mitral or aoic valves after rheumatic fever. In such instances calcification leads to impeded blood flow because it produces inflexible valve leaflets and narrowed valve orifice (mitral and aoic stenosis). Dystrophic calcification in atherosclerotic coronary aery contributes to narrowing of vessels. Dystrophic calcification also plays a role in diagnostic radiography. - Mammography is based principally on the detection of calcification in breast cancers. - Diagnosis of congenital toxoplasmosis and infection involving the central nervous system is suggested by visualization of calcification in the infant brain.