Cervix Totally Explained

Everything about The Cervix totally explained

The cervix (from Latin "neck") is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall. Approximately half its length is visible with appropriate medical equipment; the remainder lies above the vagina beyond view. It is occasionally called "cervix uteri", or "neck of the uterus".

Anatomy

Ectocervix

The portion projecting into the vagina is referred to as the portio vaginalis or ectocervix. On average, the ectocervix is 3 cm long and 2.5 cm wide. It has a convex, elliptical surface and is divided into anterior and posterior lips.

External os

The ectocervix's opening is called the external os. The size and shape of the external os and the ectocervix varies widely with age, hormonal state, and whether the woman has had a vaginal birth. In women who have not had a vaginal birth the external os appears as a small, circular opening. In women who have had a vaginal birth, the ectocervix appears bulkier and the external os appears wider, more slit-like and gaping.

Endocervical canal

The passageway between the external os and the uterine cavity is referred to as the endocervical canal. It varies widely in length and width, along with the cervix overall. Flattened anterior to posterior, the endocervical canal measures 7 to 8 mm at its widest in reproductive-aged women.

Internal os

The endocervical canal terminates at the internal os which is the opening of the cervix inside the uterine cavity.

Cervical crypts

There are pockets in the lining of the cervix known as cervical crypts. They function to produce cervical fluid.

Histology

The epithelium of the cervix is varied. The ectocervix (more distal, by the vagina) is composed of nonkeratinized stratified squamous epithelium The endocervix (more proximal, within the uterus) is composed of simple columnar epithelium.
   The area adjacent to the border of the endocervix and ectocervix is known as the 'transformation zone. The Transformation zone undergoes metaplasia numerous times during normal life. When the endocervix is exposed to the harsh acidic environment of the vagina it undergoes metaplasia to squamous epithelium which is better suited to the vaginal environment. Similarly when the ectoocervix enters the less harsh uterine area it undergoes metaplasia to become columnar epithelium.
   Times in life when this metaplasia of the transformation zone occurs:
- puberty; when the endocervix everts (moves out) of the uterus - with the changes of the cervix associated with the normal menstrual cycle - post-menopause; the uterus shrinks moving the transformation zone upwards
   All these changes are normal and the occurrence is said to be physiological.
   However all this metaplasia does increase the risk of cancer in this area - the transformation zone is the most common area for cervical cancer to occur.
   At certain times of life, the columnar epithelium is replaced by metaplastic squamous epithelium, and is then known as the transformation zone. Nabothian cysts are often found in the cervix.

Cervical mucus

After a menstrual period ends, the external os is blocked by mucus that's thick and acidic. This "infertile" mucus blocks spermatozoa from entering the uterus. For several days around the time of ovulation, "fertile" types of mucus are produced: they've a higher water content, are less acidic, and have a ferning pattern that helps guide spermatozoa through the cervix. This ferning is a branching pattern seen in the mucus when observed with low magnification.
Some methods of fertility awareness involve estimating a woman's periods of fertility and infertility by observing changes in her body. Among these changes are several involving the quality of her cervical mucus: the sensation it causes at the vulva, its elasticity (spinnbarkeit), its transparency, and the presence of ferning.
During pregnancy the cervix is blocked by a special antibacterial mucosal plug which prevents infection, somewhat similar to its state during the infertile portion of the menstrual cycle. The mucus plug comes out as the cervix dilates in labor or shortly before.

Cervical position

After menstruation and directly under the influence of estrogen, the cervix undergoes a series of changes in position and texture. During most of the menstrual cycle, the cervix remains firm, like the tip of the nose, and is positioned low and closed. However, as a woman approaches ovulation, the cervix becomes softer, and rises and opens in response to the high levels of estrogen present at ovulation.

Lymphatic drainage

The lymphatic drainage of the cervix is along the uterine arteries and cardinal ligaments to the parametrial, external iliac vein, internal iliac vein, and obturator and presacral lymph nodes. From these pelvic lymph nodes, drainage then proceeds to the paraaortic lymph nodes. In some women, the lymphatics drain directly to the paraaortic nodes.

Additional images

Image:Illu repdt female.jpg|Organs of the female reproductive system. Image:Illu ovaryb.jpg|Ovary Image:Illu cervix.jpg|Uterus and uterine tubes. Image:Gray1167.svg|Posterior half of uterus and upper part of vagina. Further Information

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