dystrophy(redirected from corneal dystrophiy)
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degeneration, a pathological process arising from metabolic disturbances and characterized by the appearance in the tissues of altered metabolic products (quantitatively and qualitatively).
Dystrophy is a process that lies at the basis of the development of numerous diseases. Among its mechanisms of development are infiltration, or impregnation (for example, infiltration by protein of the epithelium of the renal tubules in nephroses, lipoid infiltration of the inner wall of the arteries in atherosclerosis); distorted synthesis (for example, synthesis of hemomelanin in malaria); conversion (of fats and carbohydrates into proteins, or of proteins and carbohydrates into fats); and decomposition, or phanerosis (decomposition of the lipoproteins of the cell membranes; for example, of the elastic fibers of the aorta in syphilitic mesaortitis). The dystrophies include disorders of blood and lymph circulation or innervation, hypoxia, infections, intoxications, disruptions of the hormonal (endocrine disorders) and enzymal (enzymopathies) balance, and other metabolic disturbances. Protein, fat, carbohydrate, and mineral dystrophies are distinguished, depending on the predominant type of metabolic disturbance. The morphological manifestations of impaired metabolism can be found either within the cells or outside them, or evenly in both the cells and the intercellular substance. Dystrophies can be thus classified as cellular, noncellular, and mixed. Dystrophies may be either general (systemic) or local.
The development of protein dystrophies, or dysproteinoses, is connected with the entry of pathological proteins into the cells or the intercellular substance, with distorted protein synthesis, or with the disintegration of tissue structures; in this case the protein changes both physicochemically and morphologically. The cellular dysproteinoses include granular, or parenchymatous (changes in the functional tissue of the liver, kidneys, and muscle fibers of the heart); hyalin-drop (formation of hyalin within the cells in the form of spheres or drops), dropsical (appearance of droplets of fluid in the cytoplasm or nucleus, leading to the disintegration of the cell), and horny. The noncellular dystrophies include mucoid swelling, fibrinoid changes (deposit of a heterogeneous substance called fibrinoid, in whose formation all elements of the connective tissue and blood proteins take part, and noted in allergic conditions, collagenoses, and certain infectious diseases), hyalinosis, and amyloidosis. The mixed dysproteinoses include a large number of dystrophies that occur with the disruption of the metabolism of chromoproteins (hemosiderosis, melanosis, hemomelanosis, jaundices, and porphyrias), nucleoproteins (gout, uratic inspissation), and glycoproteins (mucous and colloidal dystrophies). Mucous dystrophy develops in the epithelium and connective tissues. The epithelial cells begin to produce a mucus-like substance (mucoid) and mucous (mucin) at an intensified rate, then die and are cast off; the condition is noted during inflammation of the mucous membranes. In the connective tissue it is most marked with tumors (chondromas, myxomas, and others). Colloid dystrophy develops in the glands (thyroid and pituitary); it is characterized by excess production of colloid and resultant distension of the follicles, death of the cells, and impregnation of the glandular tissue by the colloid.
Fat dystrophies, or lipidoses, are characterized by a change in the amount of fat in the fat storage cells, the appearance of lipids in places where they do not usually occur, and a change in the quantity and quality of lipids in the cells and tissues. Disruption of the metabolism of neutral fat is manifested in a decrease or increase in its reserves and may be general or local. A general decrease in the amount of fatty tissue is typical of emaciation (cachexia), while local decrease is typical of regional lipodystrophy (lipoatrophy), or atrophy of the fatty tissue of particular areas of the body. A special form is progressive lipodystrophy—Barraquer’s and Simmonds’ diseases—which is expressed by the disappearance of fat in the head, neck, and thorax. A general increase in fat reserves leads to obesity, while a local increase is observed with the atrophy of functional tissue or an organ (fat substitution) and in Dercum’s disease—the development of fat deposits in diffuse form or in the form of separate nodes (lipomas). Disruption of the metabolism of the lipoids (phosphatides) of the cytoplasm (cellular lipoidoses) is most often encountered in the parenchymatous organs (myocardium, liver, and kidneys); less frequently, it is characterized by the deposit of various types of lipoids (system lipoidoses) in the reticular-endothelial system: cerebroside and kerasin in Gaucher’s disease, lecithin in Niemann-Pick disease, cholesterol in Hand-Schüller-Christian disease. Noncellular fat dystrophy (noncellular lipoidosis) of the blood vessels is the basis of atherosclerosis.
The carbohydrate dystrophies involve disruption of the metabolism of polysaccharides, mucopolysaccharides, and glycoproteins. The disruption of glycogen metabolism is most important. These conditions are most clearly marked in diabetes mellitus, where tissue reserves of glycogens are sharply decreased, and in glycogenoses—Gierke’s disease and others—during which glycogen is deposited in excessive amounts in the liver, heart, kidneys, and skeletal muscles.
Among the mineral dystrophies, the most important are disturbances in the metabolism of potassium, calcium, iron, and copper. An increase in the amount of potassium in the blood and tissues is noted in Addison’s disease. A deficiency of potassium explains the occurrence of the hereditary disease periodic paralysis (familial myoplegia, paroxysmal paralysis—characterized by sudden attacks of flaccid paralysis of the skeletal muscles). Disruptions of calcium metabolism—calcareous dystrophies, or tissue decal-cifications—are characterized by the precipitation of calcium in the tissues in the form of dense masses. A distinction is made between metastatic (calcareous metastases), dystrophic (petrification), and metabolic (calcareous gout, calcinosis) tissue decalcification. In calcareous metastases, which are associated with hypercalcemia (increased calcium content in the blood), widespread decalcification of organs and tissues (lungs, stomach, kidneys, heart, and arteries) is observed; in dystrophic decalcification the calcium is deposited in tissues that are in a state of necrobiosis, or necrotic. Metabolic decalcification may be general or local. Iron is contained mainly in hemoglobin; disruptions of its metabolism are linked with hemoglobinogenic pigments (chromoproteins) and are expressed by hemosiderosis (deposit of the pigment hemosiderin in the skin as dark brown spots, as well as in internal organs) and hemochromatosis (melanodermia, pigment cyrrhosis, bronzed diabetes-characterized by the deposit of the pigments hemosiderin, hemofuscin, and melanin in the liver, pancreas, lymph nodes, myocardium, and elsewhere; simultaneous with the precipitation of pigment, the functional tissue is replaced by connective tissue). Hepatocerebral dystrophy, in which copper is deposited in the liver, kidneys, brain, and cornea, is a disease of impaired copper metabolism.
The mechanisms of development of dystrophy are studied with the methods of histochemistry, electron microscopy, autoradiography, and histospectrography.
REFERENCESSerov, V. V. Distrofiia. In A. I. Strukov, Patologicheskaia anatomiia. Moscow, 1967.
Davydovskii, I. V. Obshchaia patologiia cheloveka, 2nd ed. Moscow, 1969.
V. V. SEROV