The uterus is a hollow, fibromuscular, inverted pear-shaped organ situated in the middle of the lesser pelvis in the frontal plane.

The urinary bladder is located anteriorly to the uterus, while the rectum lies posteriorly.

The uterus consists of 3 parts:

Fundus - the base part, located above the site where the Fallopian tubes enter the uterus;
Body - the largest part, also the implantation site of the fertilized egg; it has a narrowing in the lower part called the isthmus that connects the body of the uterus with the cervix;
Cervix - the narrowed part that connects the uterus to the vagina; it contains the cervical canal which has two openings - internal orifice that is connected with the isthmus and external orifice - connected with the vagina.

As the lowest portion of the cervix is located in the vagina, the cervix is divided into two smaller subdivisions - supravaginal and vaginal parts.

The uterus has two surfaces:

Anterior surface (also called vesical surface) - faces the urinary bladder;
Posterior surface (or intestinal surface) - faces the sigmoid colon and coils of the ileum.

Between both surfaces are two margins - the right and the left.

The body of the uterus contains the uterine cavity, which in the coronal cut section has a shape of an inverted triangle. The cavity narrows at the region of the cervix and forms the cervical canal. It ends with the external uterine ostium - opening to the vagina.

The uterus has several openings:

External uterine ostium
Internal uterine ostium
Right and left uterine openings of the Fallopian tubes

The shape and size of the uterus depend on the age, functional state of the female, history of childbirth, and a total number of pregnancies:

Length: around 3 inches (7 - 8 cm) for nulliparous women (women who have not given birth), 3.1 - 3.7 inches (8 - 9.5 cm) for women who have given birth;
Width: approximately 1.6 to 2 inches (4 - 5 cm);
Thickness: about 1 - 1.2 inches (2.5 - 3 cm);
Weight: about 1 - 2 ounces (30 - 50 grams) for nulliparous women, 3 - 3.5 ounces (80 - 100 grams) for women who have given birth.

The normal anatomical position of the uterus is described with the following Latin terms:

Anteversio - the long axis of the uterus is bent forward towards the vagina;
Anteflexio - a displacement forward of the body of the uterus at the cervix, so the organ is bent upon itself anteriorly.

The peritoneum covers the uterus from three sides, and it does not cover the ventral aspect of the cervix.

Two pouches in the peritoneal cavity are related to the uterus:

Vesicouterine pouch - lies anterior to the uterus between the anterior surface of the uterus and the posterior surface of the urinary bladder;
Rectouterine pouch (also known as the pouch of Douglas) - situated between the posterior surface of the uterus and the anterior surface of the rectum.

The wall of the uterus is made up of three layers:

Inner mucous layer (endometrium) - consists of two parts (functional and basal); it undergoes regular morphologic changes during the menstrual cycle because of fluctuations in estrogen and progesterone levels; the functional part sheds during the menstrual phase;
Middle muscular layer (myometrium) - formed by smooth muscle cells and has three sublayers (inner longitudinal, middle circular, outer longitudinal);
External serous layer (perimetrium) - formed by the peritoneum.

The functions of the uterus include the following:

Place for attachment of fertilized egg
Development of the fetus
Provision of childbirth (the muscle contractions of the uterus help to push the baby out of the female body as the cervix dilates)
Provision of menstrual cycle
Gender difference

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Uterus