Here’s a good question someone asked about metaplasia.
Q. I have a question about metaplasia. It seems that the other types of altered cell activity are classified as either physiologic or pathologic. I understand that metaplasia occurs as a protective mechanism after a certain stress. The example given is respiratory epithelium of smokers (ciliated columnar to squamous epithelium). It’s not clear to me – is that a physiologic response to an environmental change or is the need for cells to protect themselves indicate it’s a pathologic response?
A. That’s a great question! I think the answer is that metaplasia is a physiologic response to a stimulus which is usually (but not always) pathologic. That’s a long-winded response…I’ll explain a bit.
In the lung, as you mentioned, ciliated columnar cells can undergo metaplasia in response to cigarette smoke. The metaplasia is not in and of itself pathologic; it’s more of a reactive (physiologic) change that protects the lung from the cigarette smoke. The stimulus (smoke) is pathologic; the response (metaplasia) is physiologic.
In the cervix, columnar cells undergo metaplasia too, just like in the lung. In the cervix, however, this metaplasia occurs as a part of normal aging. The endocervix (inner cervix) is lined by columnar epithelium, and the ectocervix (outer cervix) is lined by squamous epithelium. The border between these two types of epithelium is called the transformation zone. The transformation zone moves to a different place during puberty…and then to a different place again during adulthood. I’d call this metaplasia physiologic, again (like it is in the lung). The stimulus for this change, though, whatever it is, is probably not a pathologic thing – but just something that occurs during normal growth and development.
Bottom line: metaplasia is a physiologic response to some stimulus – it’s a way of protecting the body against further injury.
One additional note: sometimes metaplasia precedes other, pathologic changes. So while it’s not a pathologic thing by itself, it’s sometimes a breeding ground for other, nastier changes.
It is a good question. It’s like Barrett’s oesophagus I think. We follow them up to make sure dysplasia or outright neoplasia hasn’t developed over time. That kind of illustrates the last two paragraphs.
Exactly! Barrett’s is a great example. Many patients never develop dysplasia or carcinoma, but some do – so we monitor them carefully.
What is the difference between Metaplasia and Dysplasia?
Metaplasia is when one cell type is replaced by another; dysplasia is when a cell shows a bunch of nasty changes (like nuclear atypia, nuclear hyperchromatism, atypical cell shape, etc.). Here are a couple posts that might help: What’s the connection between dysplasia and neoplasia? and metaplasia vs. neoplasia.
metaplasia is basically change of one adult cell into another..and dysplasia is just abnormal cell growth
Yes!
dear Prof need to clarify something..please help..are myelin figures reversible or irreversible?
According to Robbins, myelin figures are reversible in early stages of ischemia. However, if the cell continues to be deprived of oxygen, irreversible changes will occur, at which point the myelin figures would be irreversible.
Dr.Kristine, whats the difference between Carcinoma in situ and dysplasia? this has always confused me, thanks for your precious time.
Carcinoma in situ is at the “bad” end of the spectrum of dysplasia: it’s one step beyond severe (or high-grade) dysplasia. It’s hard, though, to reliably differentiate between the two morphologically – so pathologists don’t always agree with each other (and even the same pathologist might call it one way one day, and another way another day). The two terms are often equated (high-grade dysplasia and carcinoma in situ).