The cervix is a cylindrical organ often described as the neck of the uterus. Located at the lowest part of the uterus, it serves as the gateway connecting the uterine cavity to the vagina. This structure is a fundamental component of the female reproductive tract, playing a dynamic role throughout a person’s life. It manages physiological functions ranging from regulating fertility to facilitating childbirth.
Physical Structure and Placement
The cervix is positioned deep within the pelvic cavity, extending from the base of the uterus into the uppermost part of the vagina. It is typically cylindrical, measuring approximately 3 to 4 centimeters in length and about 2.5 centimeters in diameter. Its size and shape vary depending on factors such as age and previous childbirth.
The structure is composed of dense, fibromuscular tissue, making it much more rigid than the rest of the uterine wall. The cervix is divided into two regions: the ectocervix, which projects into the vagina, and the endocervix, the canal connecting the uterus and the vagina.
The opening of the endocervical canal is called the external os. This opening is typically small and circular in those who have not given birth, appearing more slit-like after a vaginal delivery. The ectocervix is covered by flat, protective squamous cells, while the inner endocervical canal is lined by mucus-secreting glandular cells.
Essential Roles in Reproduction
The cervix acts as a physical and immunological barrier, helping to maintain a sterile environment within the uterus. For much of the menstrual cycle, the cervix is sealed by a thick mucus plug. This barrier prevents bacteria and pathogens from ascending from the vagina into the upper reproductive tract.
Glandular cells of the endocervix produce cervical mucus, which transforms in response to fluctuating hormone levels. Before and after ovulation, the mucus is thick and acidic, blocking sperm passage. This consistency guards the uterus against foreign substances.
As ovulation approaches, rising estrogen levels cause the mucus to become thin, clear, and watery. This change creates channels that facilitate sperm movement into the uterus and provides a nourishing medium for sperm survival. The fluid also acts as a selective filter, allowing only the most motile sperm to pass through.
Hormonal Transformations and Labor
During pregnancy, the cervix remains firm and closed, providing structural support to contain the developing fetus and amniotic fluid. As the due date approaches, the cervix begins transformation known as cervical ripening. This process is orchestrated by hormones, including prostaglandins, which soften the dense, collagen-rich tissue.
The first stage of labor involves two changes: effacement and dilation. Effacement is the thinning and shortening of the cervix, measured in percentages toward 100%. The cylindrical structure pulls up into the lower segment of the uterus.
Dilation is the opening of the external os, measured in centimeters, which must reach 10 centimeters for the baby to pass. Uterine contractions exert pressure that stretches the cervix open. This stretching triggers a positive feedback loop, promoting further contractions and accelerating dilation.
Screening and Common Health Concerns
The cervix is a common site for abnormal cell changes that can lead to cancer, due to the cellular transition zone where the ectocervix and endocervix meet. Screening tests, such as the Pap test and Human Papillomavirus (HPV) testing, detect these pre-cancerous conditions early. The HPV test looks for high-risk strains of the virus, which causes nearly all cases of cervical cancer.
The Pap test involves collecting a cell sample to examine for abnormal growth, often called dysplasia or cervical intraepithelial neoplasia. Identifying these changes allows for timely monitoring or treatment before cells progress into invasive cancer. Regular screening significantly reduces the incidence of cervical cancer worldwide.
The cervix can also be affected by non-cancerous conditions like cervicitis and cervical polyps. Cervicitis is inflammation or infection of the tissue, often caused by sexually transmitted infections, and is usually managed with medication. Cervical polyps are benign growths that may cause light bleeding but are generally harmless and easily removed.