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Cervix
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Medicine Female reproductive system
The Cervix or Cervix uteri, is the lower part of the uterus (womb) that joins to the top of the vagina in the human female reproductive system.[1] It is approximately four centimeters long, approximately half of which extends into the vaginal canal; however, the length of the cervix can be affected by age and childbirth, along with individual (genetic) variations.[2]
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A woman's cervix is the neck of the uterus, which extends into their vagina. This narrow tube or canal remains open, just big enough to allow sperms to enter or to let blood flow out during menstruation.[3] The opening into the uterus is called the , and the opening into the vagina is called the . The lower part of the cervix, known as the vaginal portion of the cervix (or ectocervix), bulges into the top of the vagina.[4] When a woman becomes pregnant, this narrow opening is sealed with a mucus plug, which forms a protective barrier for the canal. During pregnancy, a lot of changes occur in the cervix, as it softens, becomes longer, then shortens, dilates and becomes thinner as pregnancy progresses.[5]
[▲] Etymology
The word cervix came to English from Latin, where it means "neck", and like its Germanic counterpart, it can refer not only to the neck [of the body] but also to an analogous narrowed part of an object. The cervix uteri (neck of the uterus) is thus the uterine cervix, but in English the word cervix used alone usually refers to it. Thus the adjective cervical may refer either to the neck (as in cervical vertebrae or cervical lymph nodes) or to the uterine cervix (as in cervical cap or cervical cancer).
Latin cervix came from the Proto-Indo-European root ker-, referring to a "structure that projects". Thus, the word cervix is linguistically related to the English word "horn", the Persian word for "head" (sar), the Greek word for "head" (Greek: koryphe), and the Welsh word for "deer" (Welsh: carw).[]
The cervix was documented in anatomical literature in at least the time of Hippocrates; cervical cancer was first described more than 2000 years ago, with descriptions provided by both Hippocrates and Aretaeus.[] However, there was some variation in word sense among early writers, who used the term to refer to both the cervix and the internal uterine orifice.[] The first attested use of the word to refer to the cervix of the uterus was in 1702.[]
[▲] Structure
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The cervix is the part of the female reproductive system that connects the uterus (womb) to the vagina. Around 2–3 centimetres (0.8–1.2 in) in length,[] it is the lower narrower part of the uterus, which is made up of strong muscles and continuous above with the broader upper part-or body-of the uterus.[] The lower end of the cervix bulges through the anterior wall of the vagina, and is referred to as the vaginal portion of cervix (or ectocervix) while the rest of the cervix above the vagina is called the supravaginal portion of cervix.[] A central canal, known as the cervical canal, runs along its length and connects the cavity of the body of the uterus with the lumen of the vagina.[] The openings are known as the internal os and external orifice of the uterus (or external os) respectively.[] The mucosa lining the cervical canal is known as the endocervix,[] and the mucosa covering the ectocervix is known as the exocervix.[] The cervix has an inner mucosal layer, a thick layer of smooth muscle, and posteriorly the supravaginal portion has a serosal covering consisting of connective tissue and overlying peritoneum.[]
A normal cervix of an adult viewed using a bivalved vaginal speculum. The functional squamocolumnar junction surrounds the external os and is visible as the irregular demarcation between the lighter and darker shades of pink mucosa.
In front of the upper part of the cervix lies the bladder, separated from it by cellular connective tissue known as parametrium, which also extends over the sides of the cervix.[] To the rear, the supravaginal cervix is covered by peritoneum, which runs onto the back of the vaginal wall and then turns upwards and onto the rectum, forming the recto-uterine pouch.[] The cervix is more tightly connected to surrounding structures than the rest of the uterus.[]
◼ Development
As a component of the female reproductive system, the cervix is derived from the two paramesonephric ducts (also called Müllerian ducts), which develop around the sixth week of embryogenesis. During development, the outer parts of the two ducts fuse, forming a single urogenital canal that will become the vagina, cervix and uterus.[] The cervix grows in size at a smaller rate than the body of the uterus, so the relative size of the cervix over time decreases, decreasing from being much larger than the body of the uterus in fetal life, twice as large during childhood, and decreasing to its adult size, smaller than the uterus, after puberty.[] Previously it was thought that during fetal development, the original squamous epithelium of the cervix is derived from the urogenital sinus and the original columnar epithelium is derived from the paramesonephric duct. The point at which these two original epithelia meet is called the original squamocolumnar junction.[] New studies show, however, that all the cervical as well as large part of the vaginal epithelium are derived from Müllerian duct tissue and that phenotypic differences might be due to other causes.[]
[▲] References
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[2]- In a non-pregnant woman, the cervix is usually 2 to 3 cm long and roughly cylindrical in shape.
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