Mammalian Fertilisation

Gametes

Process

• Sperm swims through the uterus.
• If sperm enters at about the time of ovulation, sperm may meet the ovum in the oviduct.
• The sperm are attracted to the ovum by chemicals released from it.
• Once the sperm reaches the ovum, the chemicals released from surrounding cells trigger the acrosome reaction in the sperm.
• The acrosome swells, fusing with the sperm cell surface membrane.
• Digestive enzymes in the acrosome are released.
• The enzymes digest through the follicle cells and zona pellucida surrounding the ovum.
• This triggers the cortical reaction; the egg cell releases the contents of vesicles called cortical granules into the space between the cell membrane and the zona pellucida.
• These chemicals cause the zona pellucida to thicken and prevent entry from other sperm (polyspermy)
• The sperm nucleus that enters the egg fuses with egg nucleus to produce a fertilised egg, a zygote.