Blog89: Commonly asked questions about Metaplasia

Blog 89: Commonly asked questions about Metaplasia
Q1.What is the definition of Metaplasia?
Ans: Metaplasia is defined as a type of cellular adaptation in which one diferrentiated cell type( Epithelial or mesenchymal) is replaced by another.

(Fig1: Metaplasia,p.c- Wikipedia)
Q2. What is the most common type of metaplasia?
Ans: In respiratory tract in response to chronic stress like cigarette smoke, foreign substances the delicate columnar epithelial cells are replaces by tougher squamous epithelial cells to withstand these harmful stimuli. This is squamous metaplasia of respiratory tract.

(Fig2: Squamous metaplasia,p.c-wikipedia)

Q3. What is the mechanism of metaplasia?
Ans: Metaplasia occurs due to reprogramming of the precursor cells (from which the mature/differentiated cells develope) due to change in the environment.Normally precursor cells into mature cells with the help of specific growth factors. Due to change in the environment, there is change in the growth factors, which leads to differentiation/maturation of precursor cells in an alternate path.

Q4.What are the types of metaplasia?
Ans: Metaplasia can be classified broadly into Epithelial metaplasia & Connective tissue metaplasia.
A) Epithelial metaplasia:

Figure: Squamous metaplasia in Pap smear

• Squamous metaplasia: a. Respiratory tract: discussed above. b. Cervix: associated with chronic inflammation.            
• Columnar metaplasia: The original epithelium is replaced by columnar epithelium.a.Barretts oesophagus/Barretts metaplasia: replacement of the squamous eypithelium by mucous  secreting epithelium  for protection against HCL.b.Intestinal metaplasia: gastric glands are replaced by the glands lining the intestine.
  
             (Fig3:Barrett's oesophagus,p.c-nejm)

B) Connective tissue metaplasia:

Osseous metaplasia: Formation of bone within muscle at the site of injury(Myositis ossificans).                                                           

Q5. What is  tubal metaplasia?

Ans: In endocervical canal the non ciliated columnar epithelium is replaced by the ciliated columnar epithelium(like fallopian tube).

(Fig4:Tubal metaplasia,p.c-www.webpathology.com)

Q6. What is metaplastic squamous cell in PAP smear?

Ans: Due to chronic irritation the columnar lining of the cervical canal is transformed into squamous cells to fight against harsh environment.

Q7. What is Apocrine metaplasia?

Ans: It is observed in fibrocystic breast disease.Here the ductal cells have abundant eosinophilic cytoplasm due to increased number of mitochondria.

(Fig5:Apocrine metaplasia,p.c-wikipedia)

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