Metaplasia Flashcards
What is Metaplasia?
A reversible change where one differentiated cell type is replaced by another cell type.
Why does Metaplasia occur?
It may be due to an adaptive substitution of cells that are sensitive to stress by cell types better able to withstand the adverse environment (physical/chemical stresses etc)
Give a common example of metaplasia
The more fragile columnar epithelium in the respiratory tract can be replaced by rugged stratified squamous epithelium in response to chronic irritation (like smoking)
Explain how metaplasia is a double edge sword (and often undesirable) using the respiratory tract example
Although the respiratory tract becomes stronger, other important protective mechanisms are lost. Such as mucous secretion and ciliary action
Why is metaplasia dangerous?
The influences that predispose for metaplasia may then initiate malignant transformation in metaplastic epithelium
Describe Barrett esophagus
Squamous to columnar metaplasia in the esophagus. It is influenced by refluxed gastric acid and may lead to cancer (adenocarcinoma)
Describe connective tissue metaplasia
Formation of cartilage, bone, adipose tissue in tissues that normally do not contain these elements - example is myositis ossificans (ossification of muscle) after intramuscular hemorrage
What is the mechanism of metaplasia?
The reprogramming of stem cells normally present in the tissues or of undifferentiated mesenchymal cells .
The differentiation is achieved by signals of cytokines, GFs, and ECM components –> they alter the activity of transcription factors and regulate differentiation by gene expression
