Page 69 - Textbook of Pathology, 6th Edition

53 CHAPTER 3

Figure 3.37 Dystrophic calcification in degenerated tunica media Figure 3.38 Metastatic calcification in tubular basement membrane Cell Injury and Cellular Adaptations
of muscular artery of uterine myometrium in Mönckeberg’s arterio- in nephrocalcinosis due to hypercalcaemia.
sclerosis.

Pathogenesis of dystrophic calcification. It is not quite clear 2. Milk-alkali syndrome caused by excessive oral intake of
as to how dystrophic calcification takes place. Since serum calcium in the form of milk and administration of calcium
calcium levels are within normal limits, the denatured carbonate in the treatment of peptic ulcer.
proteins in necrotic or degenerated tissue bind phosphate 3. Hypercalcaemia of infancy is another condition in which
ions, which react with calcium ions to form precipitates of metastatic calcification may occur.
calcium phosphate. Sites of metastatic calcification. Metastatic calcification may
The process of dystrophic calcification has been likened
to the formation of normal hydroxyapatite in the bone occur in any normal tissue of the body but affects the
involving 2 phases: initiation and propagation. following organs more commonly:
1. Kidneys, especially at the basement membrane of tubular
Initiation is the phase in which precipitates of calcium epithelium and in the tubular lumina causing nephro-
phosphate begin to accumulate intracellularly in the calcinosis (Fig.3.38).
mitochondria, or extracellularly in membrane-bound 2. Lungs, especially in the alveolar walls.
vesicles.
3. Stomach, on the acid-secreting fundal glands.
Propagation is the phase in which minerals deposited in 4. Blood vessels, especially on the internal elastic lamina.
the initiation phase are propagated to form mineral crystals. 5. Cornea is another site affected by metastatic calcification.
METASTATIC CALCIFICATION. Since metastatic calcifi- 6. Synovium of the joint causing pain and dysfunction.
cation occurs in normal tissues due to hypercalcaemia, its Pathogenesis of metastatic calcification. Metasatic
causes would include one of the following two conditions: calcification at the above-mentioned sites occurs due to
Excessive mobilisation of calcium from the bone. excessive binding of inorganic phosphate ions with calcium
Excessive absorption of calcium from the gut. ions, which are elevated due to underlying metabolic
derangement. This leads to formation of precipitates of
Excessive mobilisation of calcium from the bone. These calcium phosphate at the preferential sites. Metastatic
causes are more common and include the following: calcification is reversible upon correction of underlying
1. Hyperparathyroidism which may be primary such as due metabolic disorder.
to parathyroid adenoma, or secondary such as from The distinguishing features between the two types of
parathyroid hyperplasia, chronic renal failure etc. pathologic calcification are summarised in Table 3.6.
2. Bony destructive lesions such as multiple myeloma,
metastatic carcinoma. CELLULAR ADAPTATIONS
3. Prolonged immobilisation of a patient results in disuse For the sake of survival on exposure to stress, the cells make
atrophy of the bones and hypercalcaemia. adjustments with the changes in their environment (i.e.
Excessive absorption of calcium from the gut. Less often, adapt) to the physiologic needs (physiologic adaptation) and
excess calcium may be absorbed from the gut causing to non-lethal pathologic injury (pathologic adaptation). Broadly
hypercalcaemia and metastatic calcification. These causes are speaking, such physiologic and pathologic adaptations occur
as under: by following processes (Fig. 3.39):
1. Hypervitaminosis D results in increased calcium Decreasing or increasing their size i.e. atrophy and
absorption. hypertrophy respectively, or by increasing their number i.e.