The endometrium — the uterine lining, composed of a hormonally responsive stratum functionalis (with spiral/coiled arteries) overlying a stable stratum basalis (with straight arteries) — undergoes three cyclic phases driven by ovarian hormones: menstrual shedding of the stratum functionalis, estrogen-driven proliferative regeneration of that layer and its vasculature and glands, and progesterone-driven secretory thickening and gland secretion in preparation for implantation. This is a hormonal-target-organ feedback mechanism within human reproductive physiology, in which the fate of the corpus luteum (sustained by hCG if fertilization occurs, or regressing into the corpus albicans if it does not) determines progesterone availability, which in turn determines whether the endometrial cycle repeats via ischemic breakdown and shedding or is maintained to support pregnancy.
The endometrium — the uterine lining, composed of a hormonally responsive stratum functionalis (with spiral/coiled arteries) overlying a stable stratum basalis (with straight arteries) — undergoes th…