Degenerative processes are represented by dystrophy, atrophy, necrosis and apoptosis. These changes concern both a cytoplasm and a nucleus. Degenerative changes also develop in the intercellular substance and in combination with cellular pathology cause the loss of function of organs with corresponding clinical symptoms.Dystrophy – a kind of metabolic disorder characterized by excessive accumulation of different normal and abnormal substances in cells and extracellular spaces accompanied by decrease of function of cells and organs. Dystrophy occurs not only in pathology but also in a norm (for eg., keratinization of a dermal epithelium). Dystrophy can be reversible and irreversible, the latter ends by cellular death. There are four mechanisms of dystrophy development: infiltration, decomposition, perverted synthesis and transformation.
Atrophy – morphological manifestation of metabolism disturbance in cells and tissues characterized by loss of intracellular organoids and cells itself. In atrophy the size and mass of cells and organs decrease which is accompanied by the loss of their function. Atrophy develops not only in pathology but also in norm (for example in aging).
Necrosis – local massive death of cells in a living organism. The surrounding tissues react to necrosis with inflammation. The latter has for an object to remove necrotic debris (or to encapsulate it) for further reparation (healing). Outcomes of necrosis: resorption with complete regeneration, resorption with scar formation, resorption with cyst formation, resorption with ulcer formation, auto amputation (mutilation), sequestration and encapsulation. Special kinds of necrosis: infarction, gangrene, bedsore, sequester.
Apoptosis – specific kind of cellular death caused by some hormones and cytokines. Under some circumstances these agents may activate specific genes (“death genes”) that leads to activation of some enzyme systems with subsequent destruction of the nucleus and finally the whole cell. Apoptosis plays an important role in embryogenesis, hemopoesis, antitumoral resistance, in HIV-infection and in autoimmune diseases. In contrast to necrosis apoptosis does not evoke inflammation and the dead cells undergo to phagocytosis.