Uterus is a hollow, muscular organ of the female reproductive system in which an embryo implants and develops during pregnancy. When not pregnant, it lies in the pelvis, between the urinary bladder in front and the rectum behind, with its lower part projecting into the upper vagina.
Where is the uterus located?
The nonpregnant uterus normally lies within the lesser pelvis, the lower part of the bony pelvic cavity. The uterine cervix, its narrow lower region, projects into the vagina. The vaginal space surrounding this projection is called the vaginal fornix.
The uterus is usually anteverted, meaning tilted forwards relative to the vagina, and anteflexed, meaning bent forwards between its main upper region and the uterine cervix. Position varies with the fullness of the bladder and rectum, and these forward angles are not present in everyone.
The peritoneum, the membrane lining the abdominal cavity and covering many abdominal and pelvic organs, reflects between the uterus and its neighbours. It forms the vesicouterine pouch between the bladder and uterus and the rectouterine pouch between the uterus and rectum.
What are the main parts of the uterus?
The uterus has a broad upper region and a narrower lower region. Its principal named regions are distinguished by their position and their relationship to the uterine tubes, which carry the oocyte, or egg cell, towards the uterus.
| Part | Position and anatomical meaning |
|---|---|
| Fundus of uterus | Rounded upper region above the openings of the uterine tubes. |
| Body of uterus | Main central region containing most of the uterine cavity. |
| Cornua | Upper lateral regions where the uterine tubes join the uterus. |
| Uterine cervix | Narrow lower region containing the cervical canal, the passage into the vagina. |
| Lower uterine segment | Region that develops during pregnancy chiefly from the isthmus, the narrow junction between the body of uterus and uterine cervix. |
The uterine cavity is the space within the body of uterus. It communicates with the cervical canal through the internal cervical os, its upper opening. The canal opens into the vagina through the external cervical os, its lower opening.
The abdominal ostium of uterine tube is the opening at the outer end of a uterine tube into the peritoneal cavity, the potential space between the layers of peritoneum. It is not an opening in the uterine wall and should be distinguished from the tube's opening into the uterine cavity.
What are the surfaces and layers of the uterine wall?
The anterior wall of uterus faces towards the bladder, while the posterior wall of uterus faces towards the rectum. The lateral borders lie beside the attachments of the broad ligament.
The wall of the body of uterus has these layers:
- Endometrium: the inner mucosal lining, containing glands and connective tissue. Its superficial functional layer changes during the menstrual cycle, while its deeper basal layer remains to renew the lining.
- Myometrium: the thick middle layer of smooth muscle, a type of muscle that contracts without voluntary control.
- Perimetrium: the outer serous covering where the uterus is covered by peritoneum. A serous covering is a thin membrane with a smooth surface.
Where peritoneum is absent, connective tissue forms the outer covering. The uterine cervix contains more fibrous connective tissue and proportionally less smooth muscle than the body of uterus.
What supports the uterus?
The pelvic floor, a muscular support beneath the pelvic organs, helps maintain uterine position. Connective tissue around the uterine cervix provides further support through the cardinal and uterosacral ligaments.
The cardinal ligaments extend laterally from the uterine cervix and upper vagina towards the pelvic walls. The uterosacral ligaments extend backwards towards the sacrum, the bone forming the posterior wall of the pelvis.
The round ligaments help maintain the forward position of the uterus. The broad ligament is a double fold of peritoneum extending between the uterus and lateral pelvic walls; it is not the principal weight-bearing support.
What is the blood supply of the uterus?
The uterine artery, usually a branch of the internal iliac artery, provides the principal arterial supply. It approaches the uterine cervix and ascends beside the uterus, giving branches to the uterine wall.
Near the uterine cervix, the uterine artery passes above the ureter, the tube carrying urine from the kidney to the bladder. Superiorly, its branches join branches of the ovarian artery, which arises from the abdominal aorta.
Venous blood collects in the uterine venous plexus, a network of interconnected veins beside the uterus. The uterine vein drains this blood towards the internal iliac vein.
How do nerves and lymph vessels reach the uterus?
Autonomic nerves, which regulate involuntary organ activity, reach the uterus through the uterovaginal plexus, a nerve network connected to the inferior hypogastric plexus in the pelvis. This supply includes sympathetic fibres and parasympathetic fibres, with the latter reaching the plexus through the pelvic splanchnic nerves.
Lymph vessels carry tissue fluid towards lymph nodes. Drainage varies by region:
- The upper uterus drains towards lumbar lymph nodes alongside the ovarian vessels; some lymph follows the round ligament to superficial inguinal lymph nodes in the groin.
- The body of uterus drains mainly towards external iliac lymph nodes.
- The uterine cervix drains towards internal iliac lymph nodes, external iliac lymph nodes and sacral lymph nodes.
What does the uterus do?
The endometrium provides the site for implantation, the embedding of the early embryo in the uterine lining. During pregnancy, the uterus enlarges to accommodate development, while the placenta forms the interface for exchange between maternal and fetal blood.
In a typical menstrual cycle without pregnancy, the functional layer of the endometrium is shed during menstruation. During childbirth, coordinated contractions of the myometrium help move the fetus through the uterine cervix and vagina.
How can you locate the uterus in the 3D model?
In the 3D model next to this article, rotate the view and select the uterus, then isolate the selected structure. Zoom in or out, switch layers, or fade or hide other structures; rotate the view again to explore the selection from different angles.