The uterus is located within the pelvic region immediately behind and almost overlying the bladder, and in front of the sigmoid colon. The human uterus is pear-shaped and about 7.6 cm (3.0 in) long, 4.5 cm (1.8 in) broad (side to side), and 3.0 cm (1.2 in) thick. A typical adult uterus weighs about 60 grams. The uterus can be divided anatomically into four regions: The fundus – the uppermost rounded portion of the uterus, the corpus (body), the cervix and the cervical canal. The cervix protrudes into the vagina. The uterus is held in position within the pelvis by ligaments, which are called endopelvic fascia. These ligaments include the pubocervical, transverse cervical ligaments or cardinal ligaments, and the uterosacral ligaments. It is covered by a sheet-like fold of peritoneum, the broad ligament.
Diagram showing regions of the uterus
From outside to inside, regions of the uterus include:
Uterine wall thickness (cm)
||17 - 25
||15 - 25
||15 - 22
||8 - 22
The uterus has three layers, which together form the uterine wall. From innermost to outermost, these layers are as follows:
- is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer; the functional layer thickens and then is sloughed during the menstrual cycle or estrous cycle. During pregnancy, the uterine glands and blood vessels in the endometrium further increase in size and number. Vascular spaces fuse and become interconnected, forming the placenta, which supplies oxygen and nutrition to the embryo and fetus. Commensal organisms are present in the uterus and form the uterine microbiome.
- The uterus mostly consists of smooth muscle, known as "myometrium." The innermost layer of myometrium is known as the junctional zone, which becomes thickened in adenomyosis.
- Serous layer of visceral peritoneum. It covers the outer surface of the uterus.
Vertical section of mucous membrane of human uterus.
Uterus covered by the broad ligament
The uterus is primarily supported by the pelvic diaphragm, perineal body and the urogenital diaphragm. Secondarily, it is supported by ligaments and the peritoneal ligament the broad ligament of uterus.
It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each):
Normally the uterus lies in anteversion & anteflexion. In most women, the long axis of the uterus is bent forward on the long axis of the vagina, against the urinary bladder. This position is referred to as anteversion of the uterus. Furthermore, the long axis of the body of the uterus is bent forward at the level of the internal os with the long axis of the cervix. This position is termed anteflexion of the uterus. Uterus assumes anteverted position in 50% women, retroverted position in 25% women and rest have midposed uterus.
The uterus is in the middle of the pelvic cavity in frontal plane (due to ligamentum latum uteri). The fundus does not surpass the linea terminalis, while the vaginal part of the cervix does not extend below
interspinal line. The uterus is mobile and moves posteriorly under the pressure of a full bladder, or anteriorly under the pressure of a full rectum. If both are full, it moves upwards. Increased intra-abdominal pressure pushes it downwards. The mobility is conferred to it by musculo-fibrous apparatus that consists of suspensory and sustentacular part. Under normal circumstances the suspensory part keeps the uterus in anteflexion and anteversion (in 90% of women) and keeps it "floating" in the pelvis. The meaning of these terms are described below:
||"Anteverted": Tipped forward
||"Retroverted": Tipped backwards
|Position of fundus
||"Anteflexed": Fundus is pointing forward relative to the cervix
||"Retroflexed": Fundus is pointing backwards
The sustentacular part supports the pelvic organs and comprises the larger pelvic diaphragm in the back and the smaller urogenital diaphragm in the front.
The pathological changes of the position of the uterus are:
- retroversion/retroflexion, if it is fixed
- hyperanteflexion – tipped too forward; most commonly congenital, but may be caused by tumors
- anteposition, retroposition, lateroposition – the whole uterus is moved; caused by parametritis or tumors
- elevation, descensus, prolapse
- rotation (the whole uterus rotates around its longitudinal axis), torsion (only the body of the uterus rotates around)
In cases where the uterus is "tipped", also known as retroverted uterus, women may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary tract infections, fertility difficulties, and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.
Vessels of the uterus and its appendages, rear view.
Schematic diagram of uterine arterial vasculature seen as a cross-section through the myometrium
The uterus is supplied by arterial blood both from the uterine artery and the ovarian artery. Another anastomotic branch may also supply the uterus from anastomosis of these two arteries.
Afferent nerves supplying the uterus are T11 and T12. Sympathetic supply is from hypogastric plexus and ovarian plexus. Parasympathetic supply is from second, third and fourth sacral nerves.
Bilateral Müllerian ducts form during early fetal life. In males, anti-müllerian hormone (AMH) secreted from the testes leads to their regression. In females, these ducts give rise to the Fallopian tubes and the uterus. In humans the lower segments of the two ducts fuse to form a single uterus, however, in cases of uterine malformations this development may be disturbed. The different uterine forms in various mammals are due to various degrees of fusion of the two Müllerian ducts.
Various congenital conditions of the uterus can develop in utero. Though uncommon some of these are a double uterus, didelphic uterus, bicornate uterus and others.