The female reproductive system includes a number of parts. The ovaries hold the eggs which are released each month during child bearing age. They also produce sex hormones which control periods. The fallopian tubes connect the ovaries to the womb also called the uterus. When an egg is released it travels down the fallopian tube towards the womb. At this time, sperm from the male can pass into the fallopian tube where it may meet the egg and fertilise it.
Fertilised eggs pass down the fallopian tube to the womb, which holds and protects the baby during pregnancy. The lining of the womb is called the endometrium. It thickens during the menstrual cycle ready for pregnancy. The cervix is the lower part of the womb. It is the opening into the vagina. During a period or menstruation blood passes from the womb through the cervix and then to the vagina.
The vagina also opens and expands during sexual intercourse and stretches during childbirth to allow a baby to come out. On the outside of the body is the vulva.
It is made up of two pairs of lips. Between these is the opening of the vagina. Above the vagina is the urethra: a short tube that carries urine from the bladder to outside of the body and above the urethra is the clitoris: a very sensitive area that gives sexual pleasure.
In older women, the transformation zone may be higher in the cervical canal. Author: Healthwise Staff. This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information.
Your use of this information means that you agree to the Terms of Use. But, in some women pre-cancers turn into true invasive cancers. Treating cervical pre-cancers can prevent almost all cervical cancers. The goal of cervical cancer screening is to find pre-cancer or cancer early when it is more treatable and curable.
Regular screening can prevent cervical cancers and save lives. Note the presence of everted columnar epithelium occupying a large portion of the ectocervix producing ectropion.
Mature metaplastic squamous epithelium occupies most of the ectocervix. Ectropion or ectopy is defined as the presence of everted endocervical columnar epithelium on the ectocervix. It appears as a large reddish area on the ectocervix surrounding the external os Figures 1. The eversion of the columnar epithelium is more pronounced on the anterior and posterior lips of the ectocervix and less on the lateral lips.
Occasionally the columnar epithelium extends into the vaginal fornix. The whole mucosa including the crypts and the supporting stroma is displaced in ectropion. It is the region in which physiological transformation to squamous metaplasia, as well as abnormal transformation in cervical carcinogenesis, occurs. The physiological replacement of the everted columnar epithelium by a newly formed squamous epithelium is called squamous metaplasia.
The vaginal environment is acidic during the reproductive years and during pregnancy. The acidity is thought to play a role in squamous metaplasia. When the cells are repeatedly destroyed by vaginal acidity in the columnar epithelium in an area of ectropion, they are eventually replaced by a newly formed metaplastic epithelium. The irritation of exposed columnar epithelium by the acidic vaginal environment results in the appearance of sub-columnar reserve cells.
These cells proliferate producing a reserve cell hyperplasia and eventually form the metaplastic squamous epithelium. As already indicated, the metaplastic process requires the appearance of undifferentiated, cuboidal, sub-columnar cells called reserve cells Figure 1.
These eventually lift off the persistent columnar epithelium Figures 1. The exact origin of the reserve cells is not known, though it is widely believed that it develops from the columnar epithelium, in response to irritation by the vaginal acidity. The first sign of squamous metaplasia is the appearance and proliferation of reserve cells Figures 1. This is initially seen as a single layer of small, round cells with darkly staining nuclei, situated very close to the nuclei of columnar cells, which further proliferate to produce a reserve cell hyperplasia Figure 1.
Morphologically, the reserve cells have a similar appearance to the basal cells of the original squamous epithelium, with round nuclei and little cytoplasm.
As the metaplastic process progresses, the reserve cells proliferate and differentiate to form a thin, multicellular epithelium of immature squamous cells with no evidence of stratification Figure 1. The term immature squamous metaplastic epithelium is applied when there is little or no stratification in this thin newly formed metaplastic epithelium. Groups of mucin-containing columnar cells may be seen embedded in the immature squamous metaplastic epithelium at this stage.
It has been proposed that the basement membrane of the original columnar epithelium dissolves and is reformed between the proliferating and differentiating reserve cells and the cervical stroma. Squamous metaplasia usually begins at the original squamocolumnar junction at the distal limit of the ectopy, but it may also occur in the columnar epithelium close to this junction or as islands scattered in the exposed columnar epithelium.
As the process continues, the immature metaplastic squamous cells differentiate into mature stratified metaplastic epithelium Figure 1. For all practical purposes, the latter resembles the original stratified squamous epithelium.
Some residual columnar cells or vacuoles of mucus are seen in the mature squamous metaplastic epithelium, which contains glycogen from the intermediate cell layer onwards. Several cysts, called nabothian cysts follicles , may be observed in the mature metaplastic squamous epithelium 1.
Nabothian cysts are retention cysts that develop as a result of the occlusion of an endocervical crypt opening or outlet by the overlying metaplastic squamous epithelium 1.
The buried columnar epithelium continues to secrete mucus, which eventually fills and distends the cyst. The entrapped mucus gives an ivory-white to yellowish hue to the cyst on visual examination 1.
The columnar epithelium in the wall of the cyst is flattened and ultimately destroyed by the pressure of the mucus in it. The outlets of the crypts of columnar epithelium, not yet covered by the metaplastic epithelium, remain as persistent crypt openings.
The farthest extent of the metaplastic epithelium onto the ectocervix can be best judged by the location of the crypt opening farthest away from the squamocolumnar junction. Squamous metaplasia is an irreversible process; the transformed epithelium now squamous in character cannot revert to columnar epithelium. The metaplastic process in the cervix is sometimes referred to as indirect metaplasia, as the columnar cells do not transform into squamous cells, but are replaced by the proliferating sub-columnar cuboidal reserve cells.
Squamous metaplasia may progress at varying rates in different areas of the same cervix, and hence many areas of widely differing maturity may be seen in the metaplastic squamous epithelium with or without islands of columnar epithelium.
The metaplastic epithelium adjacent to the squamocolumnar junction is composed of immature metaplasia, and the mature metaplastic epithelium is found near the original squamocolumnar junction.
Further development of the newly formed immature metaplastic epithelium may take two directions 1. In the vast majority of women, it develops into a mature squamous metaplastic epithelium, which is similar to the normal glycogen-containing original squamous epithelium for all practical purposes.
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