Dynamics and stages of the necrotic process
Tissue death goes through several sequential stages. First, paranecreosis develops—reversible changes followed by necrobiosis with a predominance of catabolic and hydrolytic reactions. After cell death occurs, autolysis sets in—the decomposition of the dead substrate under the action of lysosomal enzymes. At an excessively high pH, lysosomal membranes become labile, leading to protein denaturation and the development of coagulative necrosis.
In the early stages, changes are usually indistinguishable either visually or by light microscopy. Reliable signs of irreversibility at the ultrastructural level are detected using electron microscopy.
Macroscopic features: consistency and color
Late stages of necrosis produce diverse macroscopic manifestations in the form of changes in color, tissue density, and the appearance of a specific odor:
- Liquefactive (wet) necrosis: dead tissue is flabby, contains a lot of fluid, and undergoes myomalacia.
- Coagulative (dry) necrosis: the necrotic zone is dense and dry; the tissue may become mummified.
The color of necrotic masses depends on the presence of blood, pigments, and the zone of demarcation inflammation, which creates a characteristic red-brown rim. Typical dead tissue has a white or yellowish hue. When soaked in blood, colors vary from red and brown to green due to the transformation of hemoglobin-derived pigments; bile staining is also possible. Putrefactive breakdown results in a foul odor.
Infarctions and their varieties
An infarction is a specific type of necrosis that develops due to the cessation or reduction of blood flow. Depending on the mechanism and localization, three main forms are distinguished:
- White infarct: typical for the spleen and brain.
- White infarct with a hemorrhagic rim: found in the heart and kidneys, where the rim is formed by demarcation inflammation.
- Red (hemorrhagic) infarct: develops in the lungs (often against the background of chronic venous congestion) as a result of blood soaking into the necrotic tissues.
Briefly: answers to topical questions
What changes do tissues undergo during the stages of paranecreosis and necrobiosis?
During the stages of paranecreosis and necrobiosis, tissues undergo sequential metabolic, structural, and dystrophic changes.
- Paranecreosis—metabolic and structural changes similar to necrotic ones, but retaining a reversible character.
- Necrobiosis—irreversible dystrophic changes that lead to cell death. This stage is characterized by the predominance of catabolic reactions over anabolic ones.
Which microscopic methods allow the detection of reliable signs of necrosis irreversibility?
Electron microscopy allows the detection of reliable signs of necrosis irreversibility. Such morphological criteria include:
- Destruction of internal membranes—disruption of the integrity of intracellular structures.
- Deposition of electron-dense deposits—accumulation of complexes containing proteins and calcium salts in mitochondria.
Early stages of necrosis are usually not visible using light microscopy.
What are the causes and consequences of autolysis in necrosis?
The cause of autolysis in necrosis is the release of hydrolytic enzymes from the lysosomes of dead cells and inflammatory infiltrate cells. An acidic pH is required for the activity of these enzymes.
The consequences of autolysis depend on environmental conditions:
- Substrate decomposition—pathological melting of dead tissues under the action of hydrolases.
- Coagulative necrosis—develops at an excessively high pH when lysosomal membranes become labile, hydrolases are released, and proteins denature.
Dry necrosis is dry and dense (coagulation), while wet necrosis is flabby and watery (liquefaction). The inflammatory rim is always red-brown!
Class and exam questions
What tissue changes are visible in the early stages of necrosis?
At early stages, the necrotic process is usually invisible to the naked eye and under light microscopy.
How does a white infarct differ macroscopically from a red infarct?
White infarction is observed in the spleen and brain, whereas red (hemorrhagic) infarction occurs in the lungs due to blood soaking into the dead tissue.
What determines the color of necrotic masses?
Color depends on the presence of blood, pigments, bile, and the zone of demarcation inflammation, which creates a red-brown rim.
What else to study on this topic
- Morphogenesis of necrosis and stages of paranecreosis
- The role of hydrolytic enzymes and autolysis in cell death
- Clinical and laboratory diagnostics based on blood enzymes (CK, AST, ALT, LDH)
- Electron microscopic criteria for irreversible damage
- Mechanisms of formation of white and red infarcts
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