Histology of the Uterus

The uterine wall consists of three distinct histological layers: the perimetrium, myometrium, and endometrium. The perimetrium is the thin outermost serous membrane anchoring the uterus in the pelvic cavity. The myometrium is the thickest middle layer composed of smooth muscle bundles. The endometrium is the innermost layer lining the uterine cavity with simple columnar epithelial cells.

The myometrium, composed of smooth muscle tissue bundles, contracts to facilitate expulsion of the uterine lining during menstruation and the fetus and placenta during childbirth. These coordinated contractions are essential for reproductive processes and are regulated by hormonal signals during the menstrual cycle.

The stratum functionalis, or functional layer, changes thickness in response to sex hormone levels during the menstrual cycle and sheds during menstruation. The stratum basalis, or basal layer, remains intact throughout the cycle and serves as the regenerative source for rebuilding the functional layer after menstruation.

The endometrium receives blood from straight and spiral arterioles that branch from radial arteries in the myometrium. Straight arterioles nourish the basal layer, while spiral arterioles supply the functional layer and undergo significant changes during the menstrual cycle. These vessels originate from arcuate arteries circularly arranged in the myometrium.

Beneath the simple columnar epithelium, the endometrium contains endometrial glands embedded within the endometrial stroma, a thick lamina propria region of areolar connective tissue. This vascularized tissue layer provides structural support and contains the blood vessels that nourish the endometrial tissue.

The perimetrium is a thin serous membrane that is laterally continuous with the broad ligament, which anchors the uterus within the pelvic cavity. This outermost layer provides structural support and helps maintain the uterus in its proper anatomical position within the pelvis.

During the menstrual cycle, the functional layer of the endometrium thickens in response to sex hormone levels, preparing for potential implantation. The spiral arterioles supplying this layer undergo significant changes during the cycle. After menstruation, the basal layer regenerates the functional layer for the next cycle.