97. Local atrophy: definition of the concept, causes, types. Macro- and microscopic changes in organs with local atrophy, outcomes, clinical significance.

Atrophy is a lifetime decrease in the volume of cells, tissues, and organs with a decrease or cessation of their function.

Causes of local atrophy:

1. organ inactivity (atrophy of limb muscles in case of bone fracture)

2. circulatory insufficiency (myocardial atrophy in atherosclerosis of the coronary arteries)

3. tumor pressure, aneurysm, exudate (atrophy of the renal parenchyma in violation of urine outflow - hydronephrosis)

4. violation of tissue innervation

5. exposure to physico-chemical factors (prolonged use of GCS  atrophy of the adrenal cortex)

Types of local atrophy:

1. Dysfunctional A. (from inaction): muscle atrophy in case of limb fracture, optic nerve after eye removal, edges of the dental cell after tooth extraction - the intensity of metabolism, the amount of blood and nutrients flowing in are reduced

2. A. from insufficient blood supply: atherosclerosis of the coronary arteries  myocardial atrophy; hypoxia  dystrophy of parenchymal cells, stimulation of fibroblast proliferation  sclerosis

3. A. from pressure: violation of the outflow of urine and the transformation of the kidney into a thin-walled bag of urine (hydronephrosis); based on insufficient blood flow due to compression of blood vessels

4. Neurotic A.: death of motor neurons sp/m or destruction of nerve trunks  muscle atrophy (in polio) due to trophic disorders, proliferation of connective and adipose tissue instead of muscles (false hypertrophy)

5. A. under the influence of physico-chemical factors: ionizing radiation  bone marrow atrophy; GCS  atrophy of the adrenal cortex

Morphology of the local a.: more often the organ is reduced, the surface is smooth (smooth atrophy), less often granular (granular atrophy); sometimes the organ is enlarged (hydronephrosis, hydrocephalus, false hypertrophy), but not at the expense of parenchyma

Microscopic changes in organs and tissues during atrophy. They are manifested by a decrease in the size of predominantly parenchymal cells, a densification of the cytoplasm and, to a lesser extent, nuclear structures (simple atrophy). In atrophying cells, the nuclear-cytoplasmic ratio increases, secretion products and spare nutrients disappear in conditions of oxygen deficiency, products of incomplete combustion, autooxidation and peroxidation, lipofuscin accumulate in increased quantities. This pigment is light-optically detected in the form of golden or brown grains in the cytoplasm of cells near the nuclei.It is especially found in the liver, in the fibers of skeletal muscles, in the cells of the central and autonomic nervous system, where it occurs normally, and accumulates with age. Attention is drawn to the preservation of the nucleus and the main organelles of the cytoplasm with a closer location in the cell, a decrease in their size and number, especially mitochondria and the granular cytoplasmic network containing a relatively small number of ribosomes, which indicates a decrease in protein synthesis.

As atrophic changes increase, cell nuclei are increasingly involved in the process; they decrease in volume, condense, note the accumulation of chromatin in the nuclear membrane, a decrease in the size of nucleoli In these cases, not only the volume of cells decreases, but also their number (numbering atrophy). Parenchymal cells of adipose tissue shrink during atrophy. The intercellular substance thickens, undergoes destruction, or serous fluid accumulates in it. Atrophied cells are stained more intensively with histological dyes. Collagen and elastic fibers deform and acquire basophilic properties.

The significance and outcomes of atrophy: a) reversible in the initial stages after the elimination of the causal factor b) far-reaching atrophic phenomena are irreversible