Cervix

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Cervix
Scheme female reproductive system-en.svg
Schematic frontal view of female anatomy
Female reproductive system lateral nolabel.png
1: Fallopian tube, 2: bladder, 3: pubic bone, 4: posterior fornix erogenous zone, 5: clitoris, 6: urethra, 7: vagina, 8: ovary, 9: sigmoid colon, 10: uterus, 11: fornix, 12: cervix, 13: rectum, 14: anus
LatinCervix uteri
Gray'ssubject #268 1259
ArteryVaginal artery and uterine artery
PrecursorMüllerian duct
MeSHCervix+uteri
Dorlands/Elseviercervix uteri
 
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Cervix
Scheme female reproductive system-en.svg
Schematic frontal view of female anatomy
Female reproductive system lateral nolabel.png
1: Fallopian tube, 2: bladder, 3: pubic bone, 4: posterior fornix erogenous zone, 5: clitoris, 6: urethra, 7: vagina, 8: ovary, 9: sigmoid colon, 10: uterus, 11: fornix, 12: cervix, 13: rectum, 14: anus
LatinCervix uteri
Gray'ssubject #268 1259
ArteryVaginal artery and uterine artery
PrecursorMüllerian duct
MeSHCervix+uteri
Dorlands/Elseviercervix uteri

The cervix (from the Latin cervix uteri, meaning "neck of the womb") is the inferior, narrow portion of the uterus where it joins with the superior 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. The cervix has an opening to allow semen and menstrual fluid to move through.[1]

Structure[edit]

The cervix with cervical mucus
The cervical os

Anatomy[edit]

The cervix is an anatomical structure that is continuous with the vagina and the uterus. The external opening of the cervix (Latin: external os) faces towards the vagina, and the internal opening (Latin: internal os) faces towards the uterus. The cervical canal is the portion between these two openings, and the portion of the cervix within the vagina outside of the external opening is known as the ectocervix. [2]:415 In greater detail:

Position[edit]

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, more similar to the lips, and rises and opens in response to the high levels of estrogen present at ovulation.[3] These changes, accompanied by the production of fertile types of cervical mucus, support the survival and movement of sperm.

Blood supply[edit]

Cervix is supplied by descending cervical branch of uterine artery.[4]

Lymphatic drainage[edit]

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.

Innervation[edit]

Nerves supplying the cervix pass through uterosacral ligaments.[4]

Histology[edit]

The epithelium of the cervix is varied. The ectocervix is composed of of stratified squamous epithelium without keratin, which is continuous with the adjacent vagina. The endocervix is composed of simple columnar epithelium. Underlying the epithelium is a tough layer of collagen.[5] :376

Transformation zone[edit]

The area adjacent to the border of the endocervix and ectocervix is known as the transformation zone or squamocolumnar junction.[4] 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 ectocervix enters the less harsh uterine area, it undergoes metaplasia to become columnar epithelium.

Times in life when this metaplasia of the transformation zone occurs:

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.[6] :227–228

Function[edit]

Cervical mucus[edit]

Mucus plug

Cervical mucus is produced by glands in the endocervix and is composed 90% of water. Depending on the water content which varies during the menstrual cycle the mucus functions as a barrier or a transport medium to spermatozoa: during the proliferative phase, the mucus is thin and serous to allow sperm to enter the uterus while during the secretory phase, the mucus is thick to prevent sperm from interfering with the already fertilized egg. Thick mucus also prevents pathogens from interfering with a nascent pregnancy. Cervical mucus also contains electrolytes (calcium, sodium and potassium), organic components such as glucose, amino acids and soluble proteins.[15]

Cervical mucus contains trace elements including zinc, copper, iron, mangenese and selenium, the levels of which vary dependant on cyclical hormone variation during different phases of the menstrual cycle.[16] Various enzymes have been identified in human cervical mucus. Glycerol is a natural ingredient of human cervical fluid.[17][18][19][20] Studies have shown that the amount of glycerol in cervical fluid increases during sexual excitement.[18] This increase in glycerol has been postulated to be responsible for the lubricating quality of this fertile cervical fluid and may be biologically relevant during the early phase of reproductive events.

Cervical mucus

After a menstrual period ends, the external os is blocked by mucus that is thick and acidic. This "infertile" mucus blocks spermatozoa from entering the uterus.[21] For several days around the time of ovulation, "fertile" types of mucus are produced; they have a higher water content, and are less acidic and higher in electrolytes. These electrolytes cause the 'ferning' pattern that can be observed in drying mucus under low magnification; as the mucus dries, the salts crystallize, resembling the leaves of a fern.[22]

Some methods of fertility awareness such as the Creighton Model and the Billings Method 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.[22]

Most methods of hormonal contraception work primarily by preventing ovulation, but their effectiveness is increased because they prevent the fertile types of cervical mucus from being produced. Conversely, methods of thinning the mucus may help to achieve pregnancy. One suggested method is to take guaifenesin in the few days before ovulation.[23]

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.

Clinical significance[edit]

Cervical cancer[edit]

Human papillomavirus (HPV) infection is a necessary factor in the development of nearly all cases of cervical cancer. HPV vaccines can reduce the chance of developing cervical cancer, if administered before initiation of sexual activity. Potentially pre-cancerous changes in the cervix can be detected by a Pap smear, in which epithelial cells are scraped from the surface of the cervix and examined under a microscope. Most cervical cancer is detected in this way, and without any other symptoms. When symptoms occur, they may include vaginal bleeding, discharge, or discomfort. [24] :276 With appropriate treatment of detected abnormalities, cervical cancer can be prevented. Most women who develop cervical cancer have never had a Pap smear, or have not had one within the last ten years.

Worldwide, cervical cancer is the fifth most deadly cancer in women.[25] It affects about 16 per 100,000 women per year and kills about 9 per 100,000 per year.[26] Pap smear screening has greatly reduced cervical cancer incidence and mortality in nations with regular screening programs.

Additional images[edit]

References[edit]

  1. ^ Health and Wellness for Life
  2. ^ Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell ; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. ISBN 978-0-8089-2306-0. 
  3. ^ Weschler, Toni, MPH, Taking Charge of Your Fertility, Second Edition, 2002, pp. 59, 64.
  4. ^ a b c d e Manual of Obstetrics. (3rd ed.). Elsevier 2011. pp. 1-16. ISBN 9788131225561.
  5. ^ Deakin, Barbara Young ... [et al.] ; drawings by Philip J. (2006). Wheater's functional histology : a text and colour atlas (5th ed. ed.). [Edinburgh?]: Churchill Livingstone/Elsevier. ISBN 978-0-4430-6-8508. 
  6. ^ Weschler
  7. ^ Goldenberg RL, Iams JD, Mercer BM, et al. (1998). "The preterm prediction study: the value of new vs standard risk factors in predicting early and all spontaneous preterm births. NICHD MFMU Network". Am J Public Health 88 (2): 233–8. doi:10.2105/AJPH.88.2.233. PMC 1508185. PMID 9491013. 
  8. ^ To, M. S.; Skentou, C. A.; Royston, P.; Yu, C. K. H.; Nicolaides, K. H. (2006). "Prediction of patient-specific risk of early preterm delivery using maternal history and sonographic measurement of cervical length: a population-based prospective study". Ultra Obstet Gynecol 27 (4): 362–367. doi:10.1002/uog.2773. PMID 16565989. 
  9. ^ Fonseca, Eduardo B.; et al., Ebru; Parra, Mauro; Singh, Mandeep; Nicolaides, Kypros H.; Fetal Medicine Foundation Second Trimester Screening Group (2007). "Progesterone and the risk of preterm birth among women with a short cervix". NEJM 357 (5): 462–469. doi:10.1056/NEJMoa067815. PMID 17671254. 
  10. ^ Romero, R. (2007). "Prevention of sponatneous preterm birth: the role of sonographic cervical length in identifying patients who may benefit from progesterone treatment". Ultrasound Obstet Gynecol 30 (5): 675–686. doi:10.1002/uog.5174. PMID 17899585. 
  11. ^ Singh D, Meyer W, Zambarano RJ, Hurlbert DF (February 1998). "Frequency and timing of coital orgasm in women desirous of becoming pregnant". Arch Sex Behav 27 (1): 15–29. doi:10.1023/A:1018653724159. PMID 9494687. 
  12. ^ Whipple, Beverly; Komisaruk, Barry R.; Beyer, Carlos; Carlos Beyer-Flores (2006). The science of orgasm. Baltimore: Johns Hopkins University Press. ISBN 0-8018-8490-X. 
  13. ^ Lloyd, Elisabeth Anne (2006). The Case of the Female Orgasm: Bias in the Science of Evolution. Cambridge: Harvard University Press. ISBN 0-674-02246-7. 
  14. ^ "The ideas interview: Elisabeth Lloyd". The Guardian (London). 2005-09-26. Retrieved 2010-04-28. 
  15. ^ Wagner, G.; Levin, R. J. Electrolytes in vaginal fluid during the menstrual cycle of coitally active and inactive women. 
  16. ^ Hagenfeldt et al., 1973;[full citation needed] Pandey et al., 1986.[full citation needed]
  17. ^ Huggins, George; Preti, George (1976). "Volatile constituents of human vaginal secretions". Am J Obstet Gynecol 126 (1): 129–136. PMID 961738. 
  18. ^ a b Preti, George; Huggins, George; Silverberg, Geoffrey (1979). "Alterations in the organic compounds of vaginal secretions caused by sexual arousal". Fertil Steril 32 (1): 47–54. PMID 456630. 
  19. ^ Huggins, George; Preti, George (1981). "Vaginal odors and secretions". Clinical Obstetrics and Gynecology 24 (2): 355–377. doi:10.1097/00003081-198106000-00005. PMID 7030563. 
  20. ^ Owen, Derek; Katz, David (1999). "A vaginal fluid simulant". Contraception 59 (2): 91–95. doi:10.1016/S0010-7824(99)00010-4. PMID 10361623. 
  21. ^ Westinore, Ann; Evelyn, Billings (1998). The Billings Method: Controlling Fertility Without Drugs or Devices. Toronto: Life Cycle Books. p. 37. ISBN 0-919225-17-9. 
  22. ^ a b Weschler, pp. 58–59.
  23. ^ Weschler, p. 173.
  24. ^ Davidson's principles and practice of medicine. (21st ed. ed.). Edinburgh: Churchill Livingstone/Elsevier. 2010. ISBN 978-0-7020-3084-0. 
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  26. ^ "GLOBOCAN 2002 database: summary table by cancer". Archived from the original on 2008-06-16. Retrieved 2008-10-26.