Yes, the cervix is the lower portion of the uterus. It forms the narrow passage between the main body of the uterus (called the corpus) and the vagina, functioning as a gateway between the two. While it is anatomically part of the uterus, the cervix has its own distinct tissue, its own role in reproduction, and its own set of health concerns, which is why it’s often discussed as though it were a separate structure.
Where the Cervix Sits Within the Uterus
The uterus has two main divisions: the corpus (the larger upper body) and the cervix (the narrow lower neck). The boundary between them is a tight constriction called the internal os, also known as the isthmus. Below that, a short canal runs through the cervix and ends at another opening called the external os, which faces the vagina. So the cervix is essentially a tube with a door at each end: one opening into the uterus above and one opening into the vagina below.
You can think of the uterus like an upside-down pear. The wide, rounded portion is the corpus where a pregnancy develops. The tapered bottom is the cervix, projecting slightly into the upper vagina. A healthcare provider can see and feel the external os during a pelvic exam, which is why the cervix sometimes feels like its own organ even though it’s continuous with the rest of the uterus.
Different Tissue, Different Behavior
One reason the cervix gets treated as distinct from the rest of the uterus is that it’s built from different types of cells. The outer face of the cervix (the part visible from the vagina, called the ectocervix) is covered in flat, layered cells similar to the skin inside your mouth. The inner canal of the cervix is lined with a single layer of taller, mucus-producing cells. Where these two cell types meet is called the transformation zone, and it’s the spot most vulnerable to abnormal cell changes, which is why Pap smears sample cells from that area specifically.
The interior of the corpus, by contrast, is lined with a completely different tissue: the endometrium, which thickens and sheds each menstrual cycle. The columnar cells lining the cervical canal gradually merge into the endometrial lining at the very top of the cervix, near the internal os. This transition from one tissue type to another is part of why cervical cancer and uterine (endometrial) cancer are entirely different diseases with different risk factors and different screening methods.
What the Cervix Does
The cervix plays several roles that the rest of the uterus doesn’t share. Its glands produce cervical mucus that changes throughout the menstrual cycle in response to hormones. Rising estrogen before ovulation triggers the cervix to produce thin, slippery, egg-white-consistency mucus that helps sperm travel through. After ovulation, progesterone levels rise, and the mucus becomes thicker and stickier, forming a barrier that limits what can enter the uterus.
During pregnancy, the cervix stays tightly closed and develops a mucus plug that seals off the uterus from bacteria. When labor begins, uterine contractions cause the cervix to thin out (efface) and open (dilate). In early labor, the cervix dilates to about 3 to 4 centimeters. During active labor, it continues opening from 4 to 10 centimeters. Pushing doesn’t begin until the cervix is completely dilated, at which point the baby can move through the birth canal. The uterus provides the contracting muscle power, but the cervix is the gatekeeper that must fully open before delivery can happen.
Why Screening Is Separate
The fact that the cervix is part of the uterus leads to a common misunderstanding: that a Pap smear screens for uterine cancer. It doesn’t. The Pap test checks only for abnormal cell changes on the cervix itself. There is currently no routine screening test for uterine (endometrial) cancer in people without symptoms. If uterine cancer is suspected, diagnosis requires a separate procedure, typically an endometrial biopsy or transvaginal ultrasound.
Cervical cancer is actually the only gynecologic cancer with a reliable screening test. This is possible precisely because the cervix is accessible from the vagina, and the transformation zone where precancerous changes begin can be sampled directly during a pelvic exam.
How Hysterectomy Illustrates the Distinction
Surgery offers one of the clearest illustrations of how the cervix, while part of the uterus, can be treated independently. In a total hysterectomy (the most common type), the surgeon removes both the corpus and the cervix. But in a supracervical hysterectomy, only the body of the uterus is removed while the cervix is left in place. This option is sometimes used for conditions like fibroids or endometriosis when preserving the cervix is preferred.
The fact that surgeons can remove one part while leaving the other intact reinforces the point: the cervix is part of the uterus, but it’s a structurally and functionally distinct part with its own clinical considerations. If you’ve had a supracervical hysterectomy and still have your cervix, you still need Pap smears. If you’ve had a total hysterectomy, the screening schedule changes depending on your history.