Dystrophies: Mechanisms and Classification
Dystrophy is a general pathological process associated with impaired tissue metabolism, leading to structural alterations, energy deficits, and decreased function of specialized structures. Causes: hypoxia, toxic agents, drug effects, enzymopathies, microorganisms.
Four mechanisms of development are distinguished:
- Infiltration — excessive penetration of metabolic products from blood and lymph in case of enzymatic system insufficiency.
- Decomposition (phanerosis) — breakdown of cell ultrastructures and intercellular substance.
- Perverted synthesis — formation of abnormal substances uncharacteristic of the tissue.
- Transformation — formation of products of one type of metabolism from common initial substances.
Parenchymatous Dystrophies
Protein (dysproteinemias): granular (reversible), hyaline-droplet (irreversible, outcome — focal coagulative necrosis, more common in kidneys), hydropic with cytoplasmic vacuoles and nuclear displacement (in water-electrolyte metabolism disorders, hypoxia, viral lesions), cornified (hyperkeratosis, ichthyosis, leukoplakia, "cancer pearls"). Hereditary dysproteinemias also belong here — cystinosis, tyrosinemia, phenylketonuria.
Fatty: in the myocardium — "tiger heart" with dust-like or fine-droplet steatosis and loss of striation; in the liver — "goose liver" of ochre-yellow color; in the kidneys — fat in the tubular epithelium. Hereditary lipidoses: Gaucher, Niemann–Pick, Tay–Sachs diseases.
Carbohydrate: glycogen metabolism disorders in diabetes mellitus (hyperglycemia, glucosuria, diabetic glomerulosclerosis) and in glycogenoses; glycoprotein metabolism disorders — mucous dystrophy (cystic fibrosis, mucous membrane inflammation).
Stromal-Vascular (Mesenchymal) Dystrophies
Protein — sequential disorganization of connective tissue:
- Mucoid swelling — superficial reversible disorganization, accumulation of glycosaminoglycans, metachromasia phenomenon.
- Fibrinoid swelling — irreversible destruction of fibers, eosinophilic PAS-positive masses; outcome — fibrinoid necrosis, sclerosis, hyalinosis.
- Hyalinosis — simple, lipohyalin (in diabetes), complex (in immune pathology); example — "glazed spleen".
- Amyloidosis — formation of an abnormal fibrillar protein-glycoprotein stained with Congo red and thioflavins; AL, AA, AF, ASC1 forms; "sago" and "lardaceous" spleen, "large lardaceous kidneys".
Fatty: obesity (hypertrophic and hyperplastic), cachexia, lipomatosis, lipodystrophy; cholesterol metabolism disorders — atherosclerosis, familial hypercholesterolemic xanthomatosis.
Carbohydrate: myxoid transformation of tissues, mucopolysaccharidoses (gargoylism with skeletal deformation and hepatosplenomegaly).
Necrosis and Apoptosis
Apoptosis — genetically programmed cell death that maintains tissue homeostasis. Pathology: excessive (infections), insufficient (hyperplasias), incomplete (tumors).
Necrosis — cell death in a living organism. Nuclear changes: karyopyknosis, karyorrhexis, karyolysis; cytoplasmic changes — coagulation, plasmorrhexis, plasmolysis, cytolysis. Forms: coagulative (dry), colliquative (wet), gangrene (dry, wet, anaerobic), sequestrum, infarction (white, white with a hemorrhagic rim — in the spleen, red — in the lungs). Outcomes: organization, encapsulation, petrification or purulent melting, sepsis, hemorrhage.
Circulatory Disorders
Arterial hypervolemia (hyperemia): angioneurotic, collateral, postanemic, vacuous, inflammatory.
Venous congestion: in chronic stasis — nutmeg liver, brown induration of the lungs (with hemosiderin grains in alveoli), cyanotic induration of the kidneys and spleen.
Ischemia: angiospastic, obturation, compression, redistribution; outcomes — necrobiosis, infarction, atrophy, sclerosis. Plasmorrhagia leads to hyalinosis and fibrinoid necrosis. Hemorrhage: rupture, arrosion, diapedesis.
Thrombosis : white (arteries), red (veins), mixed layered, hyaline. Embolism: thromboembolism (saddle embolus of the pulmonary artery), fat, air, gas, tissue, microbial, foreign body — cause of infarctions, sepsis, metastasis. Shock: hypovolemic, traumatic, cardiogenic, anaphylactic, septic; shock kidney with a pale cortical layer, shock liver, lung, myocardium.
Inflammation
Vascular-mesenchymal reaction to injury. Exudative inflammation:
- Serous — exudate with up to 2% protein, localization in serous and mucous membranes.
- Fibrinous — croupous (superficial necrosis, "hairy heart") and diphtheritic (deep necrosis, firmly adherent film).
- Purulent — predominance of neutrophils, histolysis; forms: abscess, phlegmon, empyema.
- Putrefactive, hemorrhagic, catarrhal.
Productive (proliferative) inflammation: interstitial (interstitial pneumonia, myocarditis, hepatitis, nephritis); around parasites and foreign bodies; granulomatous. Specific granulomas: tuberculous (caseous necrosis, epithelioid cells, lymphocytes, Pirogov–Langhans giant cells, mycobacteria), syphilitic (coagulative necrosis, plasma cells, endovasculitis, pale spirochetes), leprosum, scleroma. Outcome — sclerosis, cirrhosis, organ deformation.
Adaptation and Compensation
Atrophy — in vivo decrease in the volume of cells, tissues, and organs. General (alimentary, cancer and pituitary cachexia, cerebral) and local (dysfunctional, from circulatory insufficiency, from pressure, neurotic, from physical and chemical factors). Example — brown atrophy of the liver with accumulation of lipofuscin, thymic atrophy with Hassall's corpuscles.
Hypertrophy — increase in the volume of functioning tissue; hyperplasia — increase in the number of cells. Types: compensatory (myocardium in arterial hypertension), regenerative, vicarious (replacement), neurohumoral, false (growth of adipose or connective tissue instead of muscle tissue), hypertrophic growths (polyps, condylomata acuminata).
Sclerosis — diffuse or focal induration due to the proliferation of mature fibrous tissue. Fibrosis — moderate induration without deformation; cirrhosis — pronounced sclerosis with deformation and architectonic disturbance; scar — local focus of sclerosis. Etiology: outcome of chronic productive inflammation, connective tissue disorganization in rheumatic diseases, replacement sclerosis after necrosis, organization of thrombi and hematomas.
Key points
- Dystrophies are classified by localization (parenchymatous, stromal-vascular, mixed) and type of metabolic disorder (protein, fat, carbohydrate).
- Hyaline-droplet and fibrinoid dystrophies are irreversible and result in necrosis or sclerosis.
- Amyloidosis is verified by staining with Congo red and thioflavins; typical forms are "sago" and "lardaceous" spleen.
- Nuclear signs of necrosis: karyopyknosis, karyorrhexis, karyolysis; infarction forms differ in color and localization.
- Chronic venous congestion manifests as nutmeg liver and brown induration of the lungs with hemosiderosis.
- Fibrinous inflammation is divided into croupous and diphtheritic depending on the type of epithelium and depth of necrosis.
- Specific granulomas (tuberculous, syphilitic, leprosum, scleroma) have a characteristic cellular structure and causative agent.
- Sclerosis, fibrosis, and cirrhosis are stages and forms of connective tissue proliferation with varying degrees of organ deformation.