Fertilization, implantation and early embryonic development
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Fertilization: fusion of male and female pronuclei to form a zygote, occurring in the ampulla of the uterine tube within 24 hours of ovulation.
Implantation: embedding of the blastocyst in the endometrium, 6 to 10 days after fertilization.
Fertilization: Gamete Transport, Barriers and Capacitation
Ejaculation deposits 200 to 300 million sperms in the vagina; only a few hundred survive to reach the oocyte in the ampulla.
Sperm transport from cervix to isthmus takes 2 to 7 hours, aided by sperm motility, uterine ciliary currents, and prostaglandin/oxytocin-induced uterine contraction.
Near the ampulla, sperm regain motility via cumulus-cell chemoattractants; most sperm die within 24 hours.
Sperm cross the oocyte's three barriers, corona radiata, zona pellucida and vitelline membrane, via capacitation then acrosome reaction.
Zona pellucida is formed of glycoproteins ZP1, ZP2 and ZP3.
Capacitation: conditioning of sperm in the female genital tract over about 7 hours; removes the glycoprotein coat and seminal plasma proteins covering the sperm's acrosomal region.
Acrosome reaction: induced when capacitated sperm contacts zona pellucida glycoproteins; releases hyaluronidase and acrosin from the acrosomal cap.
Freshly ejaculated sperm are infertile and must remain in the female genital tract at least 7 hours before gaining fertilizing capacity.