Final answer:
The secretion of estrogen into the uterine tube enhances sperm migration towards the uterus where fertilization can occur. Estrogen causes muscle contractions and cilia movement in the uterine tube to facilitate the encounter of sperm with the oocyte.
Step-by-step explanation:
The migration of sperm into the uterus, where they can contact the ovum, is facilitated by the secretion of fluid into the uterine tube. High concentrations of estrogen induce contractions of the smooth muscle along the length of the uterine tube, which generates a current flowing toward the uterus. In addition, the cilia that line the outside and lumen of the uterine tube beat more strongly in response to estrogen, sweeping the oocyte-granulosa cell complex into the interior of the tube and slowly moving it toward the uterus.
Following ovulation, the oocyte is swept into the uterine tube where it may encounter sperm. The fluids in the female reproductive tract play a significant role in preparing sperm for fertilization, a process known as capacitation. Capacitation improves the motility of the spermatozoa and makes the membrane of the sperm head thinner, aiding in the release of lysosomal enzymes which are essential for penetrating the oocyte's layers. Only capacitated sperm have the ability to fertilize an oocyte. Estrogen, which is at high concentrations around the time of ovulation, causes the smooth muscle in the uterine tube to contract and cilia to beat, creating a current that directs oocytes and sperm towards the uterus for potential fertilization.