Cellular adaptation to Stress:
Hypertrophy: increased cell and organ size, often in response to increased workload; induced by growth factors produced in response to mechanical stress or other stimuli; occurs in tissues incapable of cell division
Hyperplasia: increased cell numbers in response to hormones and other growth factors; occurs in tissues whose cells are able to divide or contain abundant tissue stem cells
Atrophy: decreased cell and organ size, as a result of decreased nutrient supply or disuse; associated with decreased synthesis of cellular building blocks and increased breakdown of cellular organelles
Metaplasia: change in phenotype of differentiated cells, often in response to chronic irritation, that makes cells better able to withstand the stress; usually induced by altered differentiation pathway of tissue stem cells; may result in reduced functions or increased propensity for malignant transformation
Morphology of reversible injury:
- Cellular swelling is the first manifestation of almost all forms of injury to cells. It is a difficult morphologic change to appreciate with the light microscope; it may be more apparent at the level of the whole organ. When it affects many cells, it causes some pallor, increased turgor, and increase in weight of the organ. On microscopic examination, small clear vacuoles may be seen within the cytoplasm; these represent distended and pinched-off segments of the ER. This pattern of nonlethal injury is sometimes called hydropic change or vacuolar degeneration. Swelling of cells is reversible. Cells may also show increased eosinophilic staining, which becomes much more pronounced with progression to necrosis.
- The ultrastructural changes of reversible cell injury include:
1. Plasma membrane alterations, such as blebbing, blunting, and loss of microvilli
2. Mitochondrial changes, including swelling and the appearance of small amorphous densities
3. Dilation of the ER, with detachment of polysomes; intracytoplasmic myelln figures may be present
4. Nuclear alteration, with disaggregation of granular fibrillar elements.
©Robbins Basic Pathology, Ninth edition