Necrosis

Necrosis

NECROSIS – Pathological cell or cells death in living body due to injury.

NECROBIOSIS – It is a physiological cell death e.g. desquamation of surface epithelium.

APOPTOSIS – It is a programmed cell death, it may be pathological or physiological. In this process the nucleus is condensed the cell is divided into small membrane bounded bodies called apoptotic bodies. Eventually the apoptotic bodies are engulfed by phagocytes.

Causes –

1. Hypoxia (lack of O₂ or ischaemia) – disturbed blood supply.

2. Physical agents – Excessive heat and cold etc.

3. Chemical agents – Strong acids and alkaloids etc.

4. Immunological reactions

General features –

1. The cytoplasm is homogeneous or granular and eosinophilic.

2. The cell cytoplasm may show vacuolation.

3. The nucleus shows three types of changes …

            a. Pyknosis – It is a initial change, in which nuclear material is condensed.

            b. Karyorrhexis – The nucleus is divided into small fragments.

            c. Karyolysis – Finally the nucleus is dissolved out and disappeared.

Types of necrosis –

1. Coagulation

2. Liquefaction or colliquative necrosis

3. Caseous necrosis

1. Coagulation necrosis – It is the most common type of necrosis. It is more often caused by ischaemia and less often caused by bacterial and chemical agents. It is commonly seen in heart, kidney and spleen.

GROSSLY – The affected part is pale, firm, swollen then become yellowish, softer and shrunken.

MICROSCOPICALLY – The necrosed cells are swollen and cytoplasm is eosinophilic with nuclear changes (Pyknosis, Karyorrhexis and Karyolysis) but detail is lost (due to proteolytic enzymes which release from lysosomes) but cell membrane remain intact for days or weeks giving “tomb stone” appearance, finally dead cells are phagocytose remain cell debris behind.

Contrasting features of necrosis and apoptosis

2. Liquefaction or colliquative necrosis – It is caused by ischaemia, bacterial and fungal infection. The affected part is soft then liquefied later a cyst is form containing necrotic cell debris and macrophages. This type of necrosis is commonly seen in brain. Abscess is also an example of liquefaction necrosis.

3. Caseous necrosis – In this type of necrosis the affected area is converted into yellowish and granular cheese like material. It is commonly seen in the central part of tubercle in tuberculosis.

            Caseous necrosis seen centrally which is surrounded by epithelial cells which are covered by giant cells and loose connective tissue and these all material are covered by connective tissue.

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