a. The upper panel shows the endometrium at the proliferative phase of the cycle. During this phase, the stratum functionale (separated by the dashed line from the stratum basale) greatly thickens. 15. The lower panel shows at higher magnification the endometrial glands that extend from the stratum basale to the surface. 55. b. The upper panel shows the endometrium at the secretory phase of the cycle. The glands have acquired a corkscrew shape as the endometrium increases further in thickness. The stratum basale (below the dashed line) exhibits less dramatic changes in morphology. 20. The lower panel shows uterine glands that have been cut in a plane that is close to their long axes. Note the pronounced corkscrew shape of the glands and mucous secretion (arrows). 60. c. The upper panel shows the stratum functionale (above the dashed line). Much of the stratum functionale has degenerated and sloughed away. 15. The lower panel shows the extravasated blood and necrosis of the stratum functionale. 55.
specialized layer that facilitates the separation of the placenta The corpus luteum actively produces hormones for about from the uterine wall at the termination of pregnancy. 10 days if fertilization does not occur. As hormone levels rapidly decline, changes occur in the blood supply to the stra-The menstrual phase results from a decline in the ovarian tum functionale. Initially, periodic contractions of the walls of secretion of progesterone and estrogen. the spiral arteries, lasting for several hours, cause the stratum functionale to become ischemic. The glands stop secreting, and the endometrium shrinks in height as the stroma becomes less edematous. After about 2 days, extended periods of arterial contraction, with only brief periods of blood flow, cause disruption of the surface epithelium and rupture of the blood vessels. When the spiral arteries close off, blood flows into the stratum basale but not into the stratum functionale. Blood, uterine fluid, and sloughing stromal and epithelial cells from the stratum functionale constitute the vaginal discharge. As patches of tissue separate from the endometrium, the torn ends of veins, arteries, and glands are exposed (Fig. 23.16c). The desquamation continues until only the stratum basale remains. Clotting of blood is inhibited during this period of menstrual flow. Arterial blood flow is restricted except for the brief periods of relaxation of the walls of the spiral arteries. Blood continually seeps from the open ends of the veins. The period of menstrual fow normally lasts about 5 days. The average blood loss in the menstrual phase is 35 ml to 50 ml. Blood flow through the straight arteries maintains the stratum basale.
As noted, this process is cyclic. Figure F23.2.1 in Folder 23.3 shows a single cycle of the endometrium and then demonstrates a gravid state as it is established at the end of a secretory phase. In the absence of fertilization, cessation of bleeding would accompany the growth and maturation of new ovarian follicles. The epithelial cells would rapidly proliferate and migrate to restore the surface epithelium as the proliferative phase of the next cycle begins.
In the absence of ovulation (a cycle referred to as an anovulatory cycle), a corpus luteum does not form, and progesterone is not produced. In the absence of progesterone, the endometrium does not enter the secretory phase and continues in the proliferative phase until menstruation. In cases of infertility, biopsies of the endometrium can be used to diagnose such anovulatory cycles as well as other disorders of the ovary and endometrium.
If fertilization and implantation occur, a gravid phase replaces the menstrual phase of the cycle.