Adaptations: hypertrophy, hyperplasia and metaplasia. Microscopic & gross pathomorphology
Once a cell experiences stress it will try to adapt. Hypertrophy, hyperplasia and metaplasia are all types of cellular adaptation.
Hypertrophy
- Increased cellular size.
- If occurs in a high enough percentage of an organs cells, the entire organ will increase in size.
- Heart and kidney are of particular risk to such modification
- Microscopically, there is no change in the number of cells, only the size is increased.
Hyperplasia
- Increased cell number as a result of increased mitosis
- Can be physiological (compensatory and hormonal) or pathogenic
- Most common in epidermis, intestine, liver and bone marrow
- Size of organ will increase macroscopically, microscopically, we’ll see an increased number.
Metaplasia
- One cell type is replaced with another
- A reversible processes, commonly occurs in respiratory tract in response to inhalation of irritants (bronchial cells convert from ciliated columnar to non-ciliated squamous)
- Morphological changes in this case would include seemingly swollen respiratory tract. Microscopic morphology shows a change in cellular type. (image shows metaplastic epithelium, converting simple columnar (left) to squamous (right).
Examples: classic cases of each adaptation:
- Hypertrophy: left ventricle in long-standing hypertension; skeletal muscle in weight lifters
- Hyperplasia: endometrium under oestrogen; benign prostatic hyperplasia; regrowth of the liver after partial hepatectomy
- Metaplasia: Barrett oesophagus (squamous to intestinal-type columnar epithelium with goblet cells, from acid reflux); squamous metaplasia of the bronchi in smokers