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How do estrogen and progesterone prepare the endometrium for implantation?

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Front view anatomical diagrams of the male and female reproductive systems, with labeled organs including penis, testis, prostate gland, uterus, ovary, and vagina. — human reproductive system Organs and structures of the male and female reproductive systems.

Estrogen and progesterone work in sequence to prepare the endometrium for the implantation of a fertilized egg.

During the first half of the menstrual cycle, known as the proliferative phase, maturing ovarian follicles secrete estrogen. This hormone stimulates the endometrium to thicken and become more vascular, while the uterine glands grow taller.1

Following ovulation, the corpus luteum forms and begins secreting large amounts of progesterone. This hormone induces the secretory phase, causing the endometrial glands to become distended and tortuous and the stromal cells to swell. Progesterone further prepares the uterine wall by increasing blood supply, water content, and the secretion of glycogen to nourish the developing embryo. Additionally, progesterone inhibits muscular contractions in the uterine wall that could otherwise reject the adhering egg. If fertilization does not occur, progesterone levels fall, leading to the breakdown of the endometrial lining and the onset of menstruation.12345