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Q. Discuss the types of calcification.

The mineralisation of body tissues with calcium is a normal physiological process in tissues like bones and teeth, termed as physiological calcification. However, sometimes the visceral tissues and other soft tissues may also get calcified in many diseased states, which is called pathological calcification. In addition to the calcium salts, smaller amounts of iron, magnesium and other minerals may also be deposited.

Pathological calcification can be broadly classified into two types: Dystrophic Calcification and Metastatic Calcification.

Dystrophic calcification: When the deposition takes place in dead or dying tissues, then it is termed as dystrophic calcification. The serum calcium levels are normal and the calcium metabolism is not deranged. Though hypercalcemia is not a prerequisite for dystrophic calcification, hypercalcemia can exacerbate it. It is seen in areas of tissue necrosis of any type. It is almost always present in the atheromas of advanced atherosclerosis, associated with intimal injury in the aorta and large arteries and characterized by the accumulation of lipids. Sometimes dystrophic calcification may also indicate organ dysfunction, e.g. calcification can develop in damaged heart valves, resulting in severely compromised valve motion. Pathogenesis involves initiation and propagation where crystalline calcium phosphate is formed as the final product.

Metastatic Calcification: Due to hypercalcemia, metastatic calcification may occur in normal tissues.

The causes of hypercalcemia may be:
- increased secretion of parathyroid hormone (due to either primary parathyroid tumors or production of parathyroid hormone–related protein by other malignant tumors)
- destruction of bone (e.g. Paget's disease, Myeloma, Leukemia, etc.)
- Vitamin D - related disorders and sarcoidosis
- renal failure, in which phosphate retention leads to secondary hyperparathyroidism

Metastatic calcification can occur widely throughout the body but principally affects the interstitial tissues of the vasculature, kidneys, lungs, and gastric mucosa.

Necrosis Vs Apoptosis

Q. Mention differences between necrosis and apoptosis.

Ans : Though both necrosis and apoptosis are events of cell death, they do differ in various ways. The differences can be observed under following parameters :

a) Cell Size
The cell is enlarged (swelling) in necrosis whereas the cell is reduced (shrinkage) in apoptosis.

b) Fate of Nucleus
In necrosis, nucleus undergoes series of changes like pyknosis ( irreversible condensation of chromatin in the nucleus of a cell ) , karyorrhexis (fragmentation of nucleus) and karyolysis (complete dissolution of the chromatin of a dying cell due to the enzymatic degradation). But, in Apoptosis, nucleus undergoes fragmentation into nucleosome size fragments

c) Plasma Membrane
The plasma membrane is disrupted and is full of leakages in case of necrosis but, it is intact in cells undergoing apoptosis. Only the orientation of lipids in plasma membrane is altered in apoptosis.

d) Cellular contents
Due to ruptured plasma membrane, cellular contents undergo digestion and may leak out of the cell in necrosis. But, the cellular contents are intact in case of apoptosis. However, they may be released in apoptotic bodies.

e) Adjacent inflammation
There is no any adjacent inflammation seen in apoptosis whereas adjacent inflammation can be seen in necrosis.

f) Physiologic or pathologic role
Apoptosis is often physiologic but necrosis is always pathologic.

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Different Types of Pathological Calcification

Necrosis Vs Apoptosis