Apoptosis

Apoptosis, or programmed cell death, is internally regulated by the cell and is characterized morphologically by the production of membrane-bound apoptotic bodies (Fig. 3.10.1). It can occur as a normal phenomenon, as discussed in Ch. 2. In pathological circumstances, apoptosis can be involved in many different ways: for example loss of CD₄ T-cells in infection by the human deficiency virus (HIV), reduction in cell number in pathological atrophy, and cell loss by apoptosis rather than necrosis at the edge of infarcts. In neoplasia, there is insufficient apoptosis: the balance between apoptosis and cell proliferation is disturbed so that cell proliferation exceeds cell loss and the net result is tumour growth.

Fig. 3.10.1 Morphology of apoptosis. (A) A normal cell begins to round up; (B) increased cytoplasmic eosinophilia and breakdown of cell components; (C) the cell itself disintegrates into membrane-bound apoptotic bodies; (D) phagocytosis of the apoptotic bodies.

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