The hormones that change the endometrium from the proliferative phase to the secretory phase are estrogen and progesterone. During the proliferative phase, the endometrium gradually thickens under the action of estrogen, and the proliferative phase usually occurs on the 5th to 14th day of the menstrual cycle, when the endometrium continues to thicken under the combined action of estrogen and progesterone, the gland grows and bends, and the secretory phenomenon occurs, thus the endometrium enters the secretory phase. The secretion phase is from the 15th to 28th day of the menstrual cycle, when the blood vessels of the endometrium increase rapidly and bend, and the interstitium is loose and edematous. During this period, the endometrium is thick and fluffy, and rich in nutrients, which is conducive to the implantation of the fertilized egg and its development.