Ultrastructural changes in organelles
At the subcellular level, tissue death manifests in the early stages. Margination and aggregation of chromatin are observed in the nucleus. Mitochondria swell, their matrix loses density, and irregular calcium salt deposits form inside. In the endoplasmic reticulum, membrane swelling and fragmentation occur, the number of ribosomes decreases, and polysomes detach. Lysosomes undergo membrane rupture with lightening of the matrix. Glycogen granules completely disappear from the cytoplasmic matrix, enzymatic activity drops, and myofibrils fragment.
Changes in the nucleus and cytoplasm in light microscopy
Light microscopy reveals changes associated with the activation of ribonucleases and deoxyribonucleases.
Stages of nuclear death:
- Karyopyknosis — marked shrinkage of the nucleus.
- Karyorrhexis — disintegration of nuclear structures into separate clumps.
- Karyolysis — complete dissolution of the nucleus.
Stages of cytoplasmic changes:
- Protein denaturation and coagulation with structural compaction.
- Liquefaction (colliquation) replacing coagulation.
- Morphological stages of the cytoplasm: coagulation, plasmorrhexis (fragmentation into clumps), and plasmolysis (dissolution).
The cytoplasm acquires a bright pink color upon hematoxylin and eosin staining (increased eosinophilia) due to protein denaturation and the loss of basophilic RNA. The cell becomes glassy and acquires a "moth-eaten" appearance due to organelle destruction and glycogen washout.
Lipid transformations and stromal damage
In dead cells, damaged membranes form myelin figures—large whorls of phospholipid masses that can be phagocytosed or broken down into fatty acids. The accumulation of fatty acids shifts the pH towards the acidic side, forming calcium soaps and leading to calcification.
Necrosis also affects the extracellular matrix and fibrous structures of the stroma under the action of enzymes:
- Collagen, reticular, and elastic fibers are destroyed by neutral proteases (collagenases, elastases).
- Glycoproteins are cleaved by proteases, and lipids by lipases.
- Fibrin deposition (fibrinoid necrosis) or the formation of lipogranulomas in adipose tissue is possible in injury foci.
Briefly: answers to topical questions
What histochemical reactions and markers are used for the early diagnosis of necrosis?
Special microscopy and histochemistry methods are used for the early diagnosis of necrosis.
- Fluorescence microscopy — performed using acridine orange.
- Histochemistry (PAS reaction) — reveals a decrease or disappearance of glycogen granules from the cytoplasm (e.g., in cardiomyocyte sarcoplasm).
- Polarization microscopy — allows the detection of myofibril relaxation.
Electron microscopy is also used to identify ultrastructural signs of organelle damage.
How does the microscopic picture of coagulative necrosis differ from colliquative necrosis?
The microscopic picture of these types of necrosis differs in the state of the cytoplasm and nuclei.
| Sign | Coagulative necrosis | Colliquative necrosis |
|---|---|---|
| Cytoplasm | Compaction and coagulation of protein structures | Liquefaction (colliquation) of the cytoplasm |
| Nuclei | Hyperchromatosis and pyknotic changes appear immediately | Karyolysis, karyorrhexis, disintegration of nuclei and cytoplasm join later |
| Tissue structure | In infarct coagulative necrosis, tubule contours are preserved | Disintegration of nuclei and cytoplasm occurs |
What are the tissue-level outcomes of necrosis?
At the tissue level, several favorable outcomes of necrosis are distinguished, associated with demarcation and repair processes.
- Organization — replacement of necrotic masses with connective tissue (scarring).
- Encapsulation — delimitation of the necrotic area by a connective tissue capsule.
- Petrification — dystrophic calcification, deposition of calcium salts in necrotic masses.
- Ossification — a rare outcome characterized by the formation of bone tissue in the area of necrosis.
- Cyst — a cavity formed at the site of a large softening focus in colliquative necrosis.
- Mesoglial scar — forms when a focus of colliquative necrosis in the brain is small.
The sequence of nuclear changes is easy to remember by the acronym PKL: Pyknosis (shrinkage) → Karyorrhexis (disintegration) → Lysis (dissolution).
Class and exam questions
Why does the cytoplasm become bright pink in necrosis when stained with hematoxylin and eosin?
Increased eosinophilia occurs due to the binding of eosin to denatured cytoplasmic proteins and the loss of basophilia associated with the disappearance of ribosomal RNA.
What are the main stages the cell nucleus undergoes during necrosis?
Three successive stages are distinguished: karyopyknosis (shrinkage), karyorrhexis (fragmentation into clumps), and karyolysis (complete dissolution).
What are myelin figures and how do they form?
These are large whorls of phospholipid masses formed from damaged cell membranes as a result of lipoprotein dissociation and subsequent water intercalation.
What else to study on this topic
- Early diagnostic methods for necrosis (polarization and fluorescence microscopy)
- Ultrastructural changes in mitochondria and ER
- Mechanisms of myelin figure formation and calcification
- Enzymatic destruction of the stroma and extracellular matrix
- Features of focal coagulative and colliquative necrosis
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