Figure 1.

(a) A schematic of mammalian sperm motility in the female oviduct. The progression of spermatozoa to the oviduct is hindered by the narrow channel from the uterus, known as the uterotubal junction (UTJ). (b) Sperm detachment in the oviductal epithelium at the isthmus for mammals that exhibit oestrous. Sperm bind to female tract epithelium and, as ovulation approaches, hyperactivation accompanies sperm detachment for further progression towards the egg. (c) A schematic of the sperm–cumulus and sperm–ZP interactions during an egg–sperm encounter in the ampulla.