The sperm encounters the egg in the ampulla of the oviduct.

The oviduct, also known as the fallopian tube, is a part of the female reproductive system. It connects the ovary to the uterus and plays a crucial role in fertilization. The oviduct is divided into several sections, including the infundibulum, isthmus, ampulla, and the uterine part.

- Infundibulum: This is the funnel-shaped opening of the oviduct that is located near the ovary. It has finger-like projections called fimbriae that help capture the released egg during ovulation.
- Isthmus: The isthmus is the narrowest part of the oviduct and connects the infundibulum to the ampulla.
- Ampulla: The ampulla is the wider, middle part of the oviduct. It is the most common site of fertilization. After ovulation, the released egg is swept into the ampulla by the fimbriae. This is where the sperm and egg meet and fertilization occurs.
- Fundus: The fundus is the part of the oviduct closest to the uterus. It connects the ampulla to the uterine part of the oviduct.

During sexual intercourse, sperm are ejaculated into the vagina. From there, they swim through the cervix and into the uterus. The sperm then continue their journey through the oviducts in search of the egg. As the sperm reach the ampulla, they encounter the egg if it has been released during ovulation.

The ampulla provides an optimal environment for fertilization to occur. It has a rich blood supply and secretes various substances that nourish and support the sperm and egg. The sperm undergo capacitation in the female reproductive tract, which enables them to penetrate the egg's protective layers and fertilize it.

Once fertilization occurs in the ampulla, the resulting embryo begins to travel towards the uterus, where it implants and develops into a pregnancy.

In summary, the sperm encounters the egg in the ampulla of the oviduct, which is the middle part of the fallopian tube. This is the most common site of fertilization and provides an optimal environment for the sperm and egg to meet and unite.