In addition to ovulation, another critical function occurs during the menstrual cycle. The woman’s body must be prepared in case fertilization occurs. Everything must be ready to nurture the developing embryo. Dur- ing the first two weeks of the cycle, estrogen causes the lining of the uterus to thicken. There is also an increase in the amount of blood that flows to this area. During the second half of the cycle, after ovulation has occurred, the follicle (now without the egg cell) develops into a yellow-colored body, the corpus luteum. The corpus luteum begins to secrete progesterone, the pregnancy hormone, which prepares the uterus for an embryo. Sperm can survive.
