The Uterine Cervix
Dr. Nelson Soucasaux, Brazilian gynecologist
The uterine cervix is the inferior [lower] and intravaginal [inside
the vagina] part of the uterus. The cervical canal is the uterine "way
in" and "way out," since the uterine cavity communicates
with the vagina by means of this narrow canal. In contrast to the uterine
corpus, the amount of smooth muscle fibers contained in the cervix is very
small, and most of its structure is constituted by dense collagenous tissue.
It is also mostly through the cervix that the uterus is kept "anchored"
and centralized inside the pelvis, and this is due to an intricate ligamentary
structure named retinaculum uteri.
These attach the uterine cervix to the pelvic bones and other pelvic
organs. The most important of these ligaments that originate in the structure
of the uterine cervix are the cardinal or cervico-lateral, the sacro-uterine
and the pubo-vesico-uterine ones. The other ligamentary structures that
also keep the uterus in its position do not originate in the cervix but
in the uterine corpus [the "body" of the uterus] and they are
mostly constituted by the broad and the round ligaments.
The cervical canal or endocervix is lined by a folded mucosa exhibiting
innumerable branching tubular-shaped glands consisting of single-layered
columnar epithelium. On the other hand, the epithelium that lines the ectocervix
(the external part of the uterine cervix) is a squamous stratified one,
identical to the vaginal. Due to the usual phenomenon of the ectopy, eversion
or ectropium of the endocervical mucosa, very frequently part of the glandular
tissue moves outward the external cervical orifice, "invading"
the ectocervix.
Anatomically and physiologically, the cervical canal is the "transition
point" between the higher and the lower parts of the female genital
tract. The mucous secretion produced by the endocervical glands plays an
important role in the cervical physiology. This secretion exerts a control
upon the penetration of the spermatozoa inside the uterus and, in normal
conditions, reduces the ascension of bacteria and other microorganisms towards
the upper parts of the female genitals.
The mucous secretion produced by the endocervical glands is highly sensitive
to the actions of the ovarian hormones. Thus, according to the hormonal
influences, it may not only facilitate the penetration of the spermatozoa
inside the uterus but also create some difficulty, though relative, to this
penetration. Higher estrogen levels cause specific changes in the cervical
secretion, by means of which it becomes more fluid and very receptive to
the spermatozoa. Conversely, progesterone inhibits the estrogenic effect
on this secretion, producing just the opposite changes: the mucous secretion
becomes thicker, less receptive and even "hostile" to the male
reproductive cells.
Under strong estrogen stimulation and in the absence of progesterone,
the endocervical secretion becomes abundant, fluid and transparent, acquiring
physico-chemical features that facilitate the quick ascension of the spermatozoa.
In this condition, when it is collected on a microscope slide, slightly
heated to dry and seen at the microscope, the endocervical secretion forms
beautiful branching crystals resembling fern leaves. Its elasticity and
capacity to form long filaments when distended [stretched] (phenomenon known
as "spinnbarkeit") also becomes maximal. Progesterone reduces
or inhibits all these changes, thickening the endocervical secretion and,
therefore, creating variable degrees of difficulty for the penetration of
the spermatozoa. Low estrogen levels also impede the adequate preparation
of the endocervical secretion, keeping it less receptive to the male reproductive
cells. Considering these facts it is obvious that, throughout the ovulatory
cycles, the period of the cycle in which the cervical secretion is more
receptive to the spermatozoa is just near ovulation [around the middle of
the menstrual cycle].
When non-infected, the cervical canal also separates the septic part
of the woman's genital tract (vulva and vagina) from the aseptic one (uterine
cavity and Fallopian tubes). Due to its content of leukocytes, in ideal
conditions the endocervical secretion seems to create some difficulty for
the ascension of bacteria and other microorganisms to the interior of the
uterus. Nevertheless, this difficulty is relative and of small magnitude,
because the endocervical mucosa almost always exhibit variable degrees of
infection and inflammation. More intense cervicitis can exert just the opposite
effect, functioning as an infectious focus for the higher parts of the genital
tract and also for the parametrium (the connective tissue that surrounds
mostly the uterine cervix, including the cardinal or cervico-lateral ligaments).
Though its walls are mostly constituted by dense connective tissue containing
only a few bundles of intermingled smooth muscle fibers, the uterine cervix
exhibits an amazing capacity of dilation and distention at the moment of
parturition [childbirth]. This is due to the great softening of its tissues
that takes place along pregnancy and that is maximal near childbirth. As
a result of this process, the uterine cervix becomes very malleable at the
moment of parturition. In spite of this, cervical lacerations resulting
from obstetric traumas were always very frequent.
The cervical canal possesses innumerable nervous endings highly sensitive
to pressure whose stimulation, by means of a reflex neuroendocrine pathway,
triggers the release of oxytocin by the hypothalamus. Thus, considering
that oxytocin is the main hormonal factor responsible for the uterine contractility,
the strong mechanical stimulation of the endocervix that takes place along
parturition indirectly triggers more and more powerful uterine contractions.
This is one of the main mechanisms of childbirth.
For several reasons, the uterine cervix functions as a kind of "shock
organ" in the female genital tract. In the uterine cervix there is
a strange focus of epithelial "unquietness," which is related
to a physiological process by which the usual eversions of the endocervical
mucosa are resurfaced by the squamous stratified epithelium typical of the
ectocervix, giving rise to the so-called "transformation zones."
A sum of irritative, inflammatory and infectious factors collaborate for
making the area of these eversions the site of sometimes problematic histological
changes. The main infectious factor responsible for the development of cervical
epithelial atypias is the HPV (Human Papillomavirus).
Fortunately, in most cases this epithelial "unquietness" is
benign, and the new squamous stratified epithelium that develops for resurfacing
the ectopic area of glandular epithelium is entirely normal. In such cases,
the result is the formation of what we call a "typical transformation
zone." However, with some frequency this cellular proliferation gives
rise to several degrees of epithelial atypias and abnormalities, resulting
in the development of "atypical transformation zones." Among the
abnormalities that may develop there we can mention, in increasing order
of severity, the slight, moderate and accentuated "cervical dysplasias"
and the carcinoma in situ of the cervix (see note below). The carcinoma
in situ of the cervix is the initial stage of cervical cancer, while
it is still restricted to the epithelium. At this stage it is non-invasive
and can be easily and successfully treated through very small surgical procedures.
As it is widely known, the "cervical dysplasias" (also known
as "cervical intraepithelial neoplasias" or "squamous intraepithelial
lesions") are epithelial abnormalities that may give origin to cervical
cancer, mostly as they aggravate and progress in severity. An accentuated
"dysplasia" or 3rd degree "cervical intraepithelial neoplasia,"
for instance, is clinically almost equivalent to the carcinoma in situ
of the cervix. On the other hand, while part of the slight "dysplasias"
or 1st degree "cervical intraepithelial neoplasias" may disappear
after clinical treatment or even spontaneously, they also may progress in
severity and give rise to more serious lesions and, finally, to cervical
cancer. In this way, all epithelial abnormalities and atypias of the uterine
cervix (detected at cytological examinations, colposcopy or biopsy), even
the low-degree ones, require great and constant medical attention.
Finally, I would like to emphasize that, concerning the prevention and
early detection of cervical pre-malignant and malignant pathologies, all
women ought to undergo a cytologic examination of the uterine cervix every
six months or, at least, once a year. Periodic cervical colposcopic examinations
should also be performed.
Note: Presently the traditionally named "cervical dysplasias"
are being mostly known as "cervical intraepithelial neoplasias"
(CIN) or, according to the new Bethesda System, "squamous intraepithelial
lesions" (SIL). A slight "dysplasia" corresponds to a 1st
degree "cervical intraepithelial neoplasia" (CIN 1). A moderate
"dysplasia" corresponds to a 2nd degree "cervical intraepithelial
neoplasia" (CIN 2), and an accentuated "dysplasia" to a 3rd
degree "cervical intraepithelial neoplasia" (CIN 3). Nevertheless,
the new Bethesda System is reducing the aforementioned three stages of "cervical
dysplasias" or "cervical intraepithelial neoplasias" that
can be found at cytological examinations to two types: the low-degree "squamous
intraepithelial lesions" (low-degree SIL) and high-degree "squamous
intraepithelial lesions" (high-degree SIL). They also have introduced
two new concepts in cervical cytology: ASCUS ("atypical squamous cells
of undetermined significance") and AGUS ("atypical glandular cells
of undetermined significance").
The text above is an updated excerpt from my book "Os Órgãos
Sexuais Femininos: Forma, Função, Símbolo e Arquétipo"
("The Female Sexual Organs: Shape, Function, Symbol and Archetype"),
published by Imago Editora, Rio de Janeiro, 1993. For more information on
the book, see page http://www.nelsonginecologia.med.br/orgaos.htm
from my website www.nelsonginecologia.med.br .
Copyright Nelson Soucasaux 1993, 2002
______________________________________
Nelson Soucasaux is a gynecologist dedicated to clinical, preventive
and psychosomatic gynecology. Graduated in 1974 by Faculdade de Medicina
da Universidade Federal do Rio de Janeiro, Brazil, he is the author of several
articles published in medical journals and of the books "Novas Perspectivas
em Ginecologia" ("New Perspectives in Gynecology") and "Os
Órgãos Sexuais Femininos: Forma, Função, Símbolo
e Arquétipo" ("The Female Sexual Organs: Shape, Function,
Symbol and Archetype"), published by Imago Editora, Rio de Janeiro,
1990, 1993.
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