The uterus or womb is the major female reproductive organ of most mammals, including humans. One end, the cervix, opens into the vagina; the other is connected on both sides to the fallopian tubes. In mammals, the four main forms in which it is found are: bipartite, as in cows; bicornuate, as in pigs; simplex, as with the pear-shaped one found in humans and horses; and duplex, found in rabbits.

Anatomy

The uterus is located inside the pelvis immediately dorsal (and usually somewhat rostral) to the urinary bladder and ventral to the rectum. It is held in place by eight ligaments (one anterior; one posterior; two lateral or broad; two uterosacral; and two round ligaments).

• It is usually slightly "anteverted" (tipped forward) but is sometimes retroverted (tipped backwards).
• Apart from the anteverted/retroverted distinction, the term "anteflexed" is sometimes used to indicate that the fundus is pointing forward relative to the cervix, or "retroflexed" when the fundus is pointing backwards. Under normal circumstances the uterus is both anteflexed and anteverted.

Outside of pregnancy, its size is several centimeters in diameter. The ovaries are also connected to uterus by the ovarian ligaments.

The uterus mostly consists of muscle, known as myometrium. The innermost layer of myometrium is known as the junctional zone, which becomes thickened in adenomyosis. The lining of the uterine cavity is called the endometrium. In most mammals, including humans, the endometrium builds a lining periodically which, if no pregnancy occurs, is shed or reabsorbed. Shedding of the endometrial lining in humans is responsible for menstrual bleeding (known colloquially as a woman's "period") throughout the fertile years of a female and for some time beyond. In other mammals there may be cycles set as widely apart as six months or as frequently as a few days.

The loose surrounding tissue is called the perimetrium.

The uterus is surrounded by peritoneum. The part of peritoneum that extends from the sides of the uterus is known as the broad ligament of the uterus.

Development

The bilateral Müllerian ducts form during early fetal life. In males, MIF 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.

Function

The main function of the uterus is to accept a fertilized ovum which becomes implanted into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, develops into a fetus and gestates until childbirth. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even in pregnancy the mass of a human uterus amounts to only about a kilogram (2.2 pounds).

Pathology

Some pathological states include:

• Prolapse of the uterus
• Carcinoma of the cervix - malignant neoplasm
• Carcinoma of the uterus - malignant neoplasm
• Ectopic pregnancy
• Fibroids - benign neoplasms
• Adenomyosis - ectopic growth of endometrial tissue within the myometrium
• Pyometra - infection of the uterus, most commonly seen in dogs

Terminology

The term uterus is commonly used within the medical and related professions, whilst the term womb is in more common usage.