Attached hereafter is a microscopic view of the significant changes in the uterus all throughout the uterine cycle. As one might recall, the uterine cycle encompasses the processes when a woman’s womb prepares and maintain the uterus lining to receive a fertilized egg. All uterine cycles are deemed to progress coordinately and in concurrent phases. Shown in the diagram are the: Early proliferative stage, Late proliferative stage, Secretory stage, and Menstrual stage.

The early proliferative phase starts at the end of a woman’s menstrual flow days 1-7. One can notice that the uterine glands in the proliferative phase are relatively small and sparse. In this phase, the epithelial cells start to develop microvilli and cilia as a response to the estrogen produced by the follicles.
At the cycle days 7-14, the rising estradiol (estrogen) levels stimulate the endometrial lining of the uterus to proliferate and thicken. Thus, the stratum functionalis is significantly thicker, while the glands are more coiled and densely packed in the ate proliferative phase.

The next phase of the uterine cycle secretory phase or more commonly known as the luteal stage. This phase always occurs from day 14 to day 28 of the cycle wherein ovulation occurs. Note that progesterone stimulated by the luteinizing hormone is the dominant hormone during this phase to prepare the corpus luteum and the endometrium for possible fertilized ovum implantation. Hence, in the diagram, the glands become more coiled in a complex manner and adapt a saw-toothed appearance while the endometrial lining reaches its maximal thickness. However, the stratum basalis and myometrium remain relatively unchanged.

If fertilization does not occur, menstruation happens. Within this phase, the placental tissue does not produce high levels of Human Chorionic Gonadotropin anymore, moreover, the corpus luteum slowly degenerates. Since the uterine lining did not receive the required levels of progesterone- hence, the spiral arteries constrict and the endometrial tissues turn ischemic. Menstruation thus causes cell death in the uterus and the sloughing of the stratum functionalis.