The uterus is the central part of the female reproductive system. It is the organ of gestation. It is a pouch with a highly vascularized interior, which opens towards the cervix on the outside and which on the back side, towards the abdomen, has two separate parts called horns that open into the fallopian tubes leading to the ovaries. With each menstrual cycle, under the effect of female hormones, its mucous membrane (or endometrium) thickens to facilitate the eventual implantation of an embryo. When fertilization occurs, the embryo lodges in it (implantation) and develops. The size of the uterus increases during the pregnancy until it is about 35 cm high. If there is no fertilization, the mucous membrane is destroyed: this is the period. At its lower end, the cervix is crossed by the cervical canal allowing communication between the vagina and the interior of the uterine body. At each end, the cervical canal is opened by an internal and an external ostium.

The uterus has, at the level of the uterine horns, two orifices that connect the uterine cavity to the fallopian tubes: the uterine ostium of the fallopian tube. It is through these openings that the spermatozoa go up in order to meet the oocyte at the level of the tubal ampulla.