Page 73 - Textbook of Pathology, 6th Edition

57 CHAPTER 3

Figure 3.43 Schematic diagram showing sequential changes in uterine cervix from normal epithelium to development of carcinoma in situ. A,
Normal mucus-secreting endocervical epithelium. B, Squamous metaplasia. C, Dysplastic change. D, Carcinoma in situ.

iii) Formation of skin warts from hyperplasia of epidermis iii) In gallbladder (normally lined by simple columnar Cell Injury and Cellular Adaptations
due to human papilloma virus. epithelium) in chronic cholecystitis with cholelithiasis.
iv) Pseudocarcinomatous hyperplasia of the skin. iv) In prostate (ducts normally lined by simple columnar
v) Intraductal epithelial hyperplasia in the breast in epithelium) in chronic prostatitis and oestrogen therapy.
fibrocystic breast disease. v) In renal pelvis and urinary bladder (normally lined by
transitional epithelium) in chronic infection and stones.
PATHOLOGIC FEATURES. There is enlargement of the vi) In vitamin A deficiency, apart from xerophthalmia, there
affected organ or tissue and increase in the number of cells is squamous metaplasia in the nose, bronchi, urinary tract,
(Fig. 3.42). This is due to increased rate of DNA synthesis lacrimal and salivary glands.
and hence increased mitoses of the cells.
2. Columnar metaplasia. There are some conditions in
which there is transformation to columnar epithelium. For
METAPLASIA
example:
Metaplasia is defined as a reversible change of one type of i) Intestinal metaplasia in healed chronic gastric ulcer.
epithelial or mesenchymal adult cells to another type of adult ii) Columnar metaplasia in Barrett’s oesophagus, in which
epithelial or mesenchymal cells, usually in response to there is change of normal squamous epithelium to columnar
abnormal stimuli, and often reverts back to normal on removal epithelium (Fig. 3.45).
of stimulus. However, if the stimulus persists for a long time,
epithelial metaplasia may transform into cancer (Fig. 3.43).
Metaplasia is broadly divided into 2 types: epithelial and
mesenchymal.
A. EPITHELIAL METAPLASIA. This is the more common
type. The metaplastic change may be patchy or diffuse and
usually results in replacement by stronger but less well-
specialised epithelium. However, the metaplastic epithelium
being less well-specialised such as squamous type, results
in deprivation of protective mucus secretion and hence more
prone to infection. Depending upon the type epithelium
transformed, two types of epithelial metaplasia are seen
squamous and columnar:
1. Squamous metaplasia. This is more common. Various
types of specialised epithelium are capable of undergoing
squamous metaplastic change due to chronic irritation that
may be mechanical, chemical or infective in origin. Some
common examples of squamous metaplasia are seen at
following sites:
i) In bronchus (normally lined by pseudostratified columnar
ciliated epithelium) in chronic smokers.
ii) In uterine endocervix (normally lined by simple columnar Figure 3.44 Squamous metaplasia of the uterine cervix. Part of the
epithelium) in prolapse of the uterus and in old age endocervical mucosa is lined by normal columnar epithelium while foci
(Fig. 3.44). of metaplastic squamous epithelium are seen at other places.