The womb, medically known as the uterus, is a muscular organ central to the female reproductive system. Its primary purpose is to receive and sustain a fertilized egg, nurturing it through development until birth. Located deep within the pelvis, the uterus is hormone-responsive, cycling through monthly changes to prepare for pregnancy.
Defining the Womb and Its Structure
The terms womb and uterus are used interchangeably, with uterus being the consistent term utilized in medical contexts. This inverted pear-shaped organ is suspended in the pelvic cavity, sitting behind the bladder and in front of the rectum. In a non-pregnant state, the uterus measures about 7.6 centimeters (3 inches) in length and weighs approximately 60 grams.
Anatomically, the organ is divided into three main sections. The uppermost portion, where the fallopian tubes connect, is the fundus. Below this is the corpus, or body, the main central cavity where pregnancy develops. The lower, narrow section is the cervix, which protrudes into the vagina and acts as a gateway to the uterine cavity.
The uterine wall is composed of three distinct layers. The outermost layer is the perimetrium, a thin protective coating. Beneath this lies the myometrium, a thick layer made primarily of smooth muscle fibers. The innermost lining is the endometrium, a mucous membrane that undergoes monthly changes in response to fluctuating hormones.
The Womb’s Role in Gestation
The uterus is structured to accommodate and protect a growing fetus during gestation. When an egg is fertilized in the fallopian tube, it travels to the uterus where it develops into a blastocyst. This blastocyst then burrows into the prepared endometrium in a process called implantation, which marks the beginning of pregnancy.
The outer layer of the implanted blastocyst forms the placenta, a temporary organ. The placenta connects with the uterine wall, supplying the developing embryo and fetus with oxygen and nutrients while removing waste products. The myometrium, the muscular middle layer, expands dramatically throughout pregnancy. Its muscle fibers stretch to increase the uterine volume up to hundreds of times its original size.
This expansion ensures a secure environment for fetal development until birth. When delivery arrives, the powerful muscle fibers of the myometrium shift from passive stretching to active, coordinated contractions. These contractions work to dilate the cervix and push the baby down the birth canal. After delivery, the myometrium contracts to expel the placenta and rapidly shrinks the uterus back toward its pre-pregnancy size.
The Womb and the Menstrual Cycle
When fertilization does not occur, the uterus functions as the site of the menstrual cycle. This monthly process is governed by an interplay of hormones, primarily estrogen and progesterone, produced by the ovaries. Estrogen stimulates the proliferation of the endometrium, causing the inner lining to thicken and become rich with blood vessels.
This thickening prepares the body for the potential implantation of a fertilized egg, ensuring a nourishing environment. Progesterone, released after ovulation, helps maintain this developed lining in a receptive state. If the egg remains unfertilized, the production of these hormones sharply declines approximately two weeks later.
This drop in hormone levels signals that pregnancy has not occurred, leading to the breakdown of the endometrium’s functional layer. The shedding of this tissue and blood through the cervix and vagina is known as menstruation. The process is cyclical, as the uterus continuously prepares for gestation and, if no pregnancy occurs, sheds its lining.