In order, though, that a sufficient number of sperm cells appear in the ampulla at the right time, a large number of sperm cells must be present in the ejaculate. Of the roughly 200 million ejaculated sperm cells only a few hundred are able to traverse the long way through the cervix, the uterus, and past the fallopian tube isthmus to the tube's ampullary region to there meet oocyte.
Along the way whole groups of sperm cells can halt at certain places and enter a phase of reduced activity. That is why a portion of the sperm cells can retain their fertilizing capability for up to 4 days.
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