31.21 : Histology of the Uterus

The uterine wall consists of three histological layers: the perimetrium, myometrium, and endometrium. The outermost perimetrium is a thin, serous membrane connected with the broad ligament on the sides, which helps anchor the uterus in the pelvic cavity. The thickest layer, myometrium, is mainly made up of smooth muscle tissue bundles. Its contractions are vital in facilitating the expulsion of the uterine lining, fetus, and placenta during menstruation and childbirth.

The endometrium is the innermost layer that lines the uterine cavity and comprises simple columnar epithelium cells facing the lumen. The luminal epithelium contains endometrial glands embedded within the endometrial stroma. The endometrium is divided into two distinct layers: the functional layer (stratum functionalis) and the basal layer (stratum basalis). The functional layer changes in response to sex hormone levels, thickening during the menstrual cycle and shedding during menstruation. At the same time, the stratum basalis remains intact and serves as the source to regenerate the functional layer.

The uterus is supplied with blood by the uterine arteries, branches of the internal iliac artery. These arteries form arcuate arteries, which are circularly arranged in the myometrium. From the arcuate arteries, radial arteries penetrate deep into the myometrium and branch into straight and spiral arterioles before reaching the endometrium. Straight arterioles nourish the basal layer, while spiral arterioles supply the functional layer, undergoing significant changes during the menstrual cycle. Uterine veins drain blood into the internal iliac veins.