Cytopathic Effects In Cell Injury

Morphology Of Cell Injury

After having discussed the molecular and biochemical mechanisms of various forms of cell injury, we now turn to morphologic changes of reversible and irreversible cell injury.

Morphologic terms used in cell injury of varying intensity and from different mechanisms are given in below and are discussed below.

Read And Learn More: General Pathology Notes

Morphology Of Reversible Cell Injury:

In older literature, the term degeneration was commonly used to denote morphology of reversible cell injury. However, since this term does not provide any information on the nature of underlying changes, currently the term retrogressive changes or simply reversible cell injury are
applied to non-lethal cell injury.

Common examples of morphologic forms of reversible cell injury are as under:

1. Hydropic change
2. Hyaline change
3. Mucoid change
4. Fatty change (discussed under intracellular accumulations)

1. Hydropic Change:

Hydropic change means accumulation of water within the cytoplasm of the cell. Other synonyms used are cloudy swelling (for gross appearance of the affected organ) and vacuolar degeneration (due to cytoplasmic vacuolation).

Hydropic swelling is an entirely reversible change upon removal of the injurious agent.

Etiology of Hydropic :

This is the commonest and earliest form of cell injury from almost all causes. The common causes include acute and subacute cell injury from various etiologic agents such as bacterial toxins, chemicals, poisons, burns, high fever, ischaemia-hypoxia, intravenous administration of hypertonic glucose or saline etc.

Pathogenesis of Hydropic :

Cloudy swelling results from impaired regulation of sodium and potassium at the level of cell membrane, favouring intracellular accumulation of sodium and escape of potassium from the cell.

This, in turn, is accompanied with rapid flow of water into the cell to maintain iso-osmotic conditions and hence cellular swelling occurs. In addition, influx of calcium too occurs.

Morphologic Features of Hydropic: 

Grossly, the affected organ such as kidney, liver, pancreas, or heart muscle is enlarged and heavy due to swelling. The cut surface bulges outwards and is slightly opaque.

• Microscopically:  The features of hydropic swelling in kidney are as under:
  • The tubular epithelial cells are swollen and their cytoplasm contains small clear unstained vacuoles and hence the term vacuolar degeneration.
  • These vacuoles represent distended cisternae of the endoplasmic reticulum.
  • Small cytoplasmic blebs may be seen.
  • The nucleus may appear pale.
  • The microvasculature of the interstitium is compressed due to swollen tubular cells.

Classification of morphologic forms of cell injury:

2. Hyaline Change:

The word ‘hyaline’ or ‘hyalin’ means glassy (hyalos = glass). Hyalinisation is a common descriptive histologic term for glassy, homogeneous, eosinophilic appearance of proteinaceousmaterial in haematoxylin and eosin-stained sections.

Though fibrin and amyloid have similar appearance, they have distinctive features and staining reactions and can be distinguished from non-specific hyaline material. Hyaline change is seen in heterogeneous pathologic conditions and may be intracellular or extracellular.

Intracellular of  Hyaline:

Intracellular hyaline is mainly seen in epithelial cells. A few examples are as follows:

• Hyaline droplets in the proximal tubular epithelial cells due to excessive reabsorption of plasma proteins in proteinuria.
• Hyaline degeneration of rectus abdominalis muscle called Zenker’s degeneration, occurring in typhoid fever. The muscle loses its fibrillar staining and becomes glassy and hyaline.
• Mallory’s hyaline represents aggregates of intermediate filaments in the hepatocytes in alcoholic liver cell injury.
• Nuclear or cytoplasmic hyaline inclusions seen in some viral infections.
• Russell bodies representing excessive immunoglobulins in the rough endoplasmic reticulum of the plasma cells.

Extracellular of  Hyaline:

Extracellular hyaline commonly termed hyalinisation is seen in connective tissues. A few examples of extracellular hyaline change are as under:

• Hyaline degeneration in leiomyomas of the uterus
• Hyalinised old scar of fibrocollagenous tissues.
• Hyaline arteriolosclerosis in renal vessels in hypertension and diabetes mellitus.
• Hyalinised glomeruli in chronic glomerulonephritis.
• Corpora amylacea seen as rounded masses of concentric hyaline laminae in the enlarged prostate in the elderly, in the brain and in the spinal cord in old age, and in old infarcts of the lung.

3. Mucoid Change:

Mucoid means mucus-like. Mucus is the secretory product of mucous glands and is a combination of proteins complexed with mucopolysaccharides.

Mucin, a glycoprotein, is its chief constituent. Mucin is normally produced by epithelial cells of mucous membranes and mucous glands, as well as by some connective tissues such as ground substance in the umbilical cord.

By convention, connective tissue mucin is termed myxoid. Epithelial and connective tissue mucin are both stained by alcian blue. However, the two can be distinguished by periodic acid-Schiff (PAS) stain: epithelial mucin stains PAS positive, while connective tissue mucin is PAS negative; the latter can, however, be stained positively with colloidal iron.

Epithelial Mucin:

Following are some examples of functional excess of epithelial mucin:

• Catarrhal inflammation of mucous membrane (for example, of respiratory tract, alimentary tract, uterus).
• Obstruction of duct leading to mucocele in the oral cavity and gallbladder.
• Cystic fibrosis of the pancreas.
• Mucin-secreting tumours (for example . Of ovary, stomach, large bowel etc)

Connective Tissue Mucin:

A few examples of disturbances of connective tissue mucin or myxoid change are as under:

• Mucoid or myxoid change in some tumours e.g. myxomas, neurofibromas, fibroadenoma, soft tissue sarcomas etc.
• Dissecting aneurysm of the aorta due to Erdheim’s medial degeneration and Marfan’s syndrome.
• Myxomatous change in the dermis in myxoedema.
• Myxoid change in the synovium in ganglion on the wrist.

Morphology of Reversibility Cell Injury:

• Degenerations or reversible cell injury depict the light microscopic appearance of changes occurring at ultrastructural level.
• Hydropic swelling is the earliest form of cell injury from various etiologies and its main features are cellular swelling due to cytoplasmic vacuoles.
• Hyaline change is intra- and extracellular deposition of pink, proteinaceous material.
• Mucoid change is deposition of mucinous material in epithelial and connective tissues in excessive amounts.