What is and where is the Cervix located?

The uterus is a component of the female reproductive region. The uterus is the organ where the fetus grows and develops. It is inverted pear-shaped, located in the pelvis, between the rectum and the bladder. The uterus has two areas: The lower area, located inside the vagina, named cervix, and the widest area, named uterus body.

The uterus body consists of two layers. The innermost layer is called “endometrium”. On the outside, the muscular layer or myometrium is placed, which is the one that performs contractions of the uterus during childbirth. The cervix is the lower fibromuscular part of the uterus. It has a cylindrical (or conical) shape, communicating the uterus with the vagina. The size and shape of the cervix varies according to age, the timing of the hormonal cycle, and the number of births. The cervix is divided into two sections: The part of the cervix closest to the uterus body is named endocervix. The portion closest to the vagina is named exocervix. The two main types of cells that cover the cervix are the squamous cells (in the exocervix) and the glandular cells (in the endocervix).

Cervix – Its location in the human body

Structure and Function of the Cervix

The cervix is the lower fibromuscular portion of the uterus that projects within the vagina; it is an anatomical component exclusive to the female in mammals. The cervix is ​​the region of the reproductive system, which is the boundary of the uterus with the vagina. It is a sphincter-shaped structure, composed by folds and crypts, whose main function is to act as a barrier separating the uterus. This function is essential for a successful pregnancy to develop.

The most prominent structure of the cervix are its rings, which are supported by a strong sheet of smooth muscle fibers, which allows it to contract or relax during estrus, to allow the semen passageway towards the uterus, or the expulsion of the fetus during the childbirth.

In the mucosa area, there are secretory cells of cervical mucus. The amount and viscosity of this secretion depends up on the predominance of estrogen or progesterone during the estrous cycle. During the estrus phase, the cervical mucus is very fluid in order to facilitate the ascent of the spermatozoa, but instead, once ovulation has happened due to progesterone, it becomes a very viscous secretion.

Cervix Diagram – Parts (labelled)

Cervix Parts

  1. Exocervix: It is surrounded by vaginal sacs. It is covered by a stratified squamous epithelium, and has multiple cell layers. The intermediate and superficial cell layers of the squamous epithelium contain glycogen.
  2. Endocervix: It is in the center of the cervix, forming the endocervical canal that connects the external cervical orifice (OCE) with the uterine cavity. It is covered by a reddish cylindrical epithelium of a single cellular layer.
  3. External cervical cavity: It communicates the cervical canal of the cervix with the internal cervical orifice. It varies according to the number of childbirths, and is placed in the nulliparous in the form of a circular aperture of little diameter; In the multiparous area, its appearance changes due to the tears of the birth, acquiring the aspect of transverse and starred cleft in cases of oblique tears, which deform the architecture of the cervix, whose consequence may be the ectropion or eversion of the endocervical epithelium.
  4. Endocervical canal extends from the external cervical orifice to the internal cervical orifice. It measures about 6 mm in diameter; it is covered of simple cylindrical endocervical epithelium secreting mucus, which allows it to be totally occluded by the cervical mucus, constituting the so-named endocervical mucous plug, which prevents the germs coming of the vulva area, vagina and exocervix ascend to the internal genitals. The mucous plug is expelled at the beginning of the prodromal birth phase, in the form of phlegm.
  5. Internal cervical cavity: It usually measures 10 mm approx., and it delimits the endocervical canal with the uterus, at a level known as isthmus. During normal pregnancy, it acts as a sphincter, which, if it has a problem and fails, can lead to cervical ineffectiveness with effacement and subsequent dilation of the cervix, causing late miscarriage and early birth.
  6. Squamous-cylindrical intersection: It is the union of the cylindrical epithelium with the squamous epithelium, and it is usually located in the external cervical orifice, but it varies according to the age, depending on the moment of the menstrual cycle, and other factors like the pregnancy, or the use of oral contraceptives.

Clinical significance

The cervix is the lowest part of the uterus, extending into the vagina. The cells of the cervix change constantly, but if the changes become abnormal, the dysplasia appears. Left untreated, dysplasia can lead into cancer. However, periodic Pap tests can detect and treat early dysplasia. Normal cells of the cervix flatten out as they grow, forming a protective layer as they move to the surface. Dysplasia begins when abnormal changes occur in cells on the surface of the cervix. Some cells may increase irregularly. Invasive cancer occurs when abnormal cells spread from the surface to the deeper parts of the cervix. Over time, cancer can invade other parts of the body.

In cervix cancer, most tumors originate in the area where the exocervix joins the endocervix, resulting in squamous cell carcinomas. Cancer occurs when normal cells in the cervix begin to transform and grow uncontrollably.

There are some risk factors related to the incidence of cervical cancer. The most important factor involved in the development of premalignant lesions is the papillomavirus infection, or human papillomavirus. The human papillomavirus is in 99% of cervical cancer. It is transmitted from one person to another through sexual relations. Most Human papillomavirus infections settle naturally.

Other factors that can be origin of this type of cancer are:

  • Smoking: Women who smoke are twice as likely to develop cancer as nonsmokers.
  • Sexual promiscuity: Women with many sexual couples, or having sex with a man who has had many sexual couples are at greater risk.
  • Sex at an early age
  • Women who have weakened immune systems by use of drugs used in other pathologies, as well as treatment for HIV, or other cancers.
  • Women suffering from genital herpes: Using oral contraceptives increases the chances of developing cervical cancer.

Cervical cancer

Cancer of the cervix – Different phases

The symptoms that women with cancer of cervix can have are:

  • Mild bleeding between menstruations, or at the end of each menstruation
  • Aching when having sex
  • Have a longer and more abundant menstrual bleeding than normal
  • Bleeding after sex relations, or during pelvic gynecological examination
  • Increased vaginal expulsion
  • Flow of blood after menopause.

Picture – Endometriosis : Difference between healthy uterus and uterus with endometriosis

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