The endometrium through the menstrual cycle

The lining of the uterus at three points in the menstrual cycle, side by side on the same muscle: at menstruation, the functional layer breaking away in blood; in the proliferative phase, under oestrogen, straight glands in a growing stroma; in the secretory phase, under progesterone, coiled, saw-toothed glands full of secretion, a swollen stroma and coiled spiral arteries. The basal layer, which is never shed, is the same in all three.