Secretory Phase

The secretory phase of the menstrual cycle starts after ovulation and spans from day 14 to day 28 in a typical 28-day cycle.

During this period, triggered by progesterone and estrogen produced by the corpus luteum, the endometrium gears up for possible embryo implantation.

As a result, the endometrium thickens to about 12-18 mm.

The endometrial glands secrete nutrients like glycogen into the uterine cavity, which helps sustain the embryo until it implants into the uterine lining.

Additionally, the cervical mucus thickens, forming a cervical plug that blocks the entry of sperm, pathogens, or other foreign materials.

Approximately one week after ovulation, these preparatory changes reach their climax, coinciding with the time a fertilized egg might arrive in the uterus.

If fertilization does not occur, the corpus luteum degenerates during the late secretory phase due to declining levels of luteinizing hormone.

The resulting fall in the progesterone and estrogen levels sets the stage for menstruation to begin on day 28, restarting the cycle.