The uterus is a hollow, thick-walled, pear-shaped organ and a central component of the female reproductive system. Its primary role is housing and nourishing a developing fetus during pregnancy. When pregnancy does not occur, it undergoes cyclical changes that result in menstruation. This muscular organ is typically 7.6 to 8 centimeters (about 3 inches) long in an adult who has not given birth, but it expands dramatically during gestation.
Precise Anatomical Placement
The uterus is situated deep within the pelvis, a bony basin that provides protection for the reproductive organs. It occupies the true pelvis, positioned immediately posterior to the urinary bladder and anterior to the rectum.
This location allows for some flexibility in its position, as the organ’s exact tilt can shift depending on the fullness of the bladder or the rectum. In most women, the uterus is tilted forward (anteversion) and bent forward at its body relative to the cervix (anteflexion). This forward orientation is considered the normal anatomical position.
Internal Structure and Composition
The uterus is structurally divided into three main regions: the fundus, the body, and the cervix. The fundus is the uppermost, rounded part, situated above where the fallopian tubes connect. Below the fundus is the corpus, or body, the large central area where a fertilized egg typically implants. The cervix is the lowest, narrow portion that connects the uterus to the vagina.
The uterine wall is composed of three distinct tissue layers. The innermost lining is the endometrium, which thickens monthly in preparation for pregnancy and is shed during the menstrual cycle if conception does not occur. Surrounding this is the myometrium, a thick layer of smooth muscle that constitutes the bulk of the wall. The myometrium’s powerful contractions are responsible for expelling the fetus during childbirth. The outermost layer is the perimetrium, a thin serous layer continuous with the abdominal lining.
Stabilization and Support System
The stability of the uterus relies on a combination of muscles and fibrous tissues within the pelvic cavity. Primary support is provided by the pelvic floor muscles, which form a hammock-like structure at the base of the pelvis. These muscles hold the pelvic organs in place and counteract downward pressure from the abdomen.
Various ligaments secure the uterus to the bony pelvis and surrounding structures. The broad ligament is a wide fold of membrane extending from the sides of the uterus to the pelvic walls. Specialized ligaments, such as the round ligaments, extend from the uterine horns and help maintain the typical forward-tilted position. The uterosacral ligaments connect the cervix posteriorly to the sacrum, providing further stability.