This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'True about metastatic calcification - \nSelect and explain. \nA. Serum ca level is normal, B. Occurs in dead/dying tissue, C. Occurs in damaged heart valves, D. Calcification starts in mitochondria', 'role': 'user'}, {'content': "Answer: D \nExplanation: Calcification\n\nThe deposition of mineral salts of calcium is a normal process in the formation of bone and cartilage. Calcium\xa0entry into dead or dying cells is usual, owing to the inability of such cells to maintain a steep calcium gradient.\n\nPathological calcification\n\nPathological calcification is the abnormal deposition of calcium salts in soft tissue.\nIt is of two types\n\nA) Metastatic\n\nMetastatic calcification reflects deranged calcium metabolism.\nIt’s a change associated with an increased calcium concentration in the serum.\nIn general, almost any disorder that increases the serum calcium level can lead to calcification in locations as the\xa0alveolar septa of the lung, renal tubules and blood vessels.\nThe fundamental abnormality is the pathological entry of the same amount of ionic calcium into the cell organelle, chiefly the mitochondria (it is suggested that mitochondria are the organelles first involved in the pathogenesis\xa0of metastatic calcification).\n\nSites of metastatic calcification\n\nBasement membrane & tubular lamina of kidney\nAlveolar wall of lungs (most common site)\nThe interstitial tissue of gastric mucosa\nSystemic arteries\nPulmonary veins\nCornea & conjunctiva\nSynovium of the joint\nTendons\nThese sites are prone to calcification because these tissues loose acid and therefore have the alkaline internal\xa0environment. Alkaline pH favours precipitation of calcium salts.\n\nB) Dystrophic calcification\n\nDystrophic calcification refers to the macroscopic deposition of calcium salts in injured tissues. This type of\xa0calcification does not simply reflect an accumulation of calcium derived from the bodies of dead cells but rather\xa0represents an extracellular deposition of calcium from the circulation or interstitial fluid.\xa0\nDenatured proteins in dead or irreversibly damaged tissue preferentially bind phosphate ions. Phosphate t ions\xa0react with calcium ions to form a precipitate or calcium phosphate. Thus necrotic tissue serves as calcium sink.\nIn many locations such as in a case of tuberculous caseous necrosis in the lung or lymph nodes, calcification\xa0has no functional consequences.\nDystrophic calcification may also occur in crucial locations such as in mitral or aortic valves after rheumatic\xa0fever. In such instances, calcification leads to impeded blood flow because it produces inflexible valve leaflets\xa0and narrowed valve orifice (mitral and aortic stenosis).\nDystrophic calcification in atherosclerotic coronary artery contributes to narrowing of vessels.\nDystrophic calcification also plays a role in diagnostic radiography,\nMammography is based principally on the detection of calcification in breast cancers.\nDiagnosis of congenital toxoplasmosis and infection involving the central nervous system is suggested by\xa0visualization of calcification in the infant's brain.", 'role': 'assistant'}]