During copulation, semen is released by the penis into the vagina (insemination). Sperms → vagina → cervical canal → uterus → isthmus ↓ Fertilization ← Ampullary-isthmic Junction ↑ Ovum (from ovary) → fimbriae → infundibulum → ampulla
Fertilization (sperm + ovum → zygote) occurs only if ovum & sperms are transported simultaneously. So all copulations do not lead to fertilization & pregnancy.
A sperm contacts with zona pellucida. It induces changes in the membrane that block entry of additional sperms.
With the help of secretions of the acrosome, sperm enter into the cytoplasm of the ovum. This causes second meiotic division of the secondary oocyte to form a second polar body and a haploid ovum (ootid).
The haploid nuclei of the sperm and ovum fuse together to form a diploid zygote.
