Full Body (Corpus) of Uterus Description
[Continued from above] . . . It is shaped like an inverted pear, with the body of the uterus forming the wide, superior region and the cervix of the uterus forming the narrow, inferior region. Several distinct regions make up the body of the uterus. The domed, superior region is known as the fundus and forms the roof of the uterus. At the lateral edges of the fundus, the Fallopian (uterine) tubes join with the uterus and expand into the central fluid-filled uterine cavity. From the junction with the Fallopian tubes, the body of the uterus narrows inferiorly until it joins with the cervix.
The corpus of the uterus can be divided into three distinct tissue layers, with each layer performing a specific function within the organ.
- The perimetrium forms the smooth outer skin of the uterus and connects it to the surrounding organs in the pelvic cavity. It is a serous membrane made of areolar connective tissue covered by a thin layer of simple squamous epithelium. The serous membrane of the perimetrium continues beyond the uterus to join the serous membranes of the peritoneum that line and cover the rest of the pelvic body cavity. Serous fluid secreted by perimetrium lubricates the surface of the uterus and prevents friction between the internal organs.
- Deep to the perimetrium is the myometrium, or muscular layer of the uterus. Layers of visceral muscle tissue make up the myometrium and give the uterus its ability to stretch and contract during pregnancy and delivery.
- The innermost layer of the uterus is the endometrium, which lines the inside of the organ and surrounds the hollow lumen of the uterus. Simple columnar epithelial tissue on the surface of the endometrium forms an interface between the uterus and the developing embryo or fetus during pregnancy. Deep to the epithelial tissues are connective tissues that contain many blood vessels to provide nutrients to the other tissues of the uterus.
The body of the uterus plays an important role in the female reproductive system during pregnancy and childbirth. During each menstrual cycle, the lining of the endometrium begins to grow and develop under the influence of female sex hormones in preparation for a zygote, or fertilized egg cell. If no zygote forms within about two weeks after ovulation, the uterine lining deteriorates and sloughs off as menses during menstruation. In the case of successful fertilization, the zygote implants itself into the uterine lining and is nurtured by the tissues of the endometrium as it grows into an embryo. Eventually the embryo grows a placenta into the endometrium to provide the vital exchange of gases, nutrients, and wastes between the fetal and maternal blood supplies. The body of the uterus also expands greatly during the later stages of pregnancy to accommodate the growing fetus. By the end of the thirty-six weeks of pregnancy, the body of the uterus has stretched to several times its normal size to accommodate the fetus, amniotic fluid, and placenta.
The body of the uterus also plays a vital role in the process of childbirth. Changing hormone levels near the end of pregnancy stimulate the smooth muscle tissue of the uterus to begin mild waves of contraction. Hormone levels continue to increase and trigger longer, stronger, and more regular contractions of the myometrium. Each contraction begins to push the fetus slowly out of the body of the uterus and into the cervix, which has been widening and opening under the influence of the same hormones. After many contractions, the smooth muscle of the myometrium propels the fetus out of the uterus, through the vaginal canal, and through the external vaginal orifice into the outside world.
Prepared by Tim Taylor, Anatomy and Physiology Instructor