The Fallopian Tubes
The optimal time for an oocyte to be fertilized is when it enters a fallopian tube. The fallopian tubes are fluid-filled, cilia-lined channels about 4-6 in (10-15 cm) long that carry the oocyte to the uterus. At ovulation, the primary oocyte completes its suspended meiosis and divides in two. A secondary oocyte and a small polar body result. If the secondary oocyte is fertilized, then it will go through another division which forms another polar body.
As the ripening egg travels along the fallopian tube, it is washed along by cilia which knock away residual nutrient cells on the outside of the egg. This array of cells leaving the cell forms a radiant cluster called the corona radiata. If sperm have made their way to the fallopian tube, then they have already been capacitated. Capacitation is the modification of a sperm's acrosomal tip that enables it to burrow into the egg. Fertilization blocks the ability of additional sperm to enter the egg. Once the nuclei of the egg and sperm cells have fused, the new cell is called a zygote. The zygote contains all the genetic information required to become a complete human being. This new life signifies the beginning of successful reproduction. As the zygotic cell divides into more cells, it travels from the fallopian tube to the uterus.
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