The uterus (from Latin "uterus", plural uteri) or womb () is the main hormone-responsive, secondary sex organ of the female reproductive system in humans, and most other mammals. Events occurring within the uterus are described with the term in utero. In the human, the lower end of the uterus, the cervix, opens into the vagina, while the upper end, the fundus, is connected to the fallopian tubes. It is within the uterus that the embryo and later fetus develops during gestation. In the human embryo, the uterus develops from the paramesonephric ducts which fuse into the single organ known as a simplex uterus. The uterus has different forms in many other animals and in some it exists as two separate uteri known as a duplex uterus. In medicine, and related professions the term uterus is consistently used, while the Germanic-derived term womb is commonly used in everyday contexts. Structure in humans
The human 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.
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; in cases of uterine malformations this fusion may be disturbed. The different uterine morphologies among the mammals are due to varying degrees of fusion of the Müllerian ducts. Various congenital conditions of the uterus can develop in utero. Though uncommon, some of these are didelphic uterus, bicornate uterus and others. Function
The reproductive function of the human uterus is to accept a fertilized ovum, which passes through the utero-tubal junction from the fallopian tube. The fertilized ovum divides mitotically to become a blastocyst, which implants into the endometrium and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, attaches to the wall of the uterus, creates a placenta, and develops into a fetus (gestates) until childbirth occurs. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even during pregnancy, the mass of a human uterus amounts to only about a kilogram (2.2 pounds). The uterus also plays a role in sexual response, by directing blood flow to the pelvis and ovaries, and to the external genitalia
There is also some evidence from rat studies that the uterus plays a role in cognition in a similar way to the ovaries.