Bianchi E, Wright GJ. Bianchi E, et al. PLoS Biol. 2020 Nov 13;18(11):e3000953. doi: 10.1371/journal.pbio.3000953. eCollection 2020 Nov. PLoS Biol. 2020. PMID: 33186358 Free PMC article. Review. NHS. 2019. How can I tell when I'm ovulating? Common Health Questions. www.nhs.uk Opens a new window [Accessed May 2020] NHS. 2020. How can I improve my chances of becoming a dad? NHS, Common health questions. www.nhs.uk Opens a new window [Accessed October 2022] FPA. 2018. Bodyworks. Your guide to understanding reproduction. Family Planning Association. Derby: McCorquodale. www.sexwise.fpa.org.uk Opens a new window [Accessed May 2020] An opening between the uterus and vagina called the cervix, allow sperm in and menstrual blood out. The vagina, or birth canal, connects the cervix to the outside of the body.

The placenta is an organ responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the fetus by the umbilical cord. The mother's blood does not mix with the blood of the fetus, but the placenta lets substances pass between the two blood supplies: The human female reproductive system working during reproduction and fertilisation. The egg is released from the ovary and moves toward the oviduct. From start to finish it takes about 10 to 11 weeks to create a new sperm cell. Both diet and lifestyle can make a difference to sperm quality. The average sperm lives only a few weeks in a man’s body and each ejaculation can set free up to 400 million sperm. This means that men have to make sperm continuously throughout their adult lives. The sperm that survive still have a long road ahead. In all, they need to travel about 18cm from the cervix through the womb to the fallopian tubes. That’s the equivalent of a human being swimming 100 lengths of an Olympic swimming pool! The fastest swimmers may find the egg in as little as 45 minutes. It can take the slowest up to 12 hours. If the sperm don’t find an egg in the fallopian tubes at the time of intercourse, they can survive inside you for up to seven days. This means that if you ovulate within this time window you could still conceive.Wallace WHB, Kelsey TW. 2010. Human ovarian reserve from conception to the menopause. PloS One 5(1): e8772. journals.plos.org Opens a new window [Accessed May 2020] Deanna also writes a series of books for middle grade readers, including JINNIE WISHMAKER, MARCUS MENDER, and ELEKTRA CHAOS.

NHS. 2018. Trying to get pregnant. Health A to Z. www.nhs.uk Opens a new window [Accessed May 2020] When the nucleus of a sperm and egg fuse together, the egg is fertilised and it develops into a fetus. During ejaculation, they travel along sperm ducts through internal reproductive glands, where they mix with seminal fluid, or semen, on the way to the penis. In addition to all the fun, your bodies are building up tension that you hope will end in orgasm. Having an orgasm also has an important biological function. In men, an orgasm propels sperm-rich semen into the vagina and up towards the cervix at roughly 10 miles per hour. The force of ejaculation gives the sperm a good head start on their way to the egg.Many eggs begin dying off almost immediately and the rest steadily decrease in number and quality as you get older. When you start your periods, only about 400,000 to 500,000 eggs remain. From here on it’s normal to lose about 1000 eggs every month. By the age of 30, scientists calculate that about 72,000 viable eggs remain. After your mid-thirties egg numbers decline more rapidly. The function of the female orgasm is less clear. Theories include that it strengthens the bond between partners, or that uterine contractions help the sperm along their way somehow. We know that a woman doesn’t need to orgasm for conception to happen, though. Uterine contractions happen even without you having an orgasm. During ejaculation the sperm pass through the sperm ducts and mix with fluids produced by the glands. The fluids provide the sperm cells with nutrients. The mixture of sperm and fluids is called semen. This passes out of the penis. Kallen, A. 2020 How Many Eggs Are Women Born With? And Other Questions About Egg Supply. Healthline. www.healthline.com/ Opens a new window [Accessed July 2020] Its main function is to allow the exchange of materials such as oxygen and nutrients between the fetus and mother whilst removing waste substances such as carbon dioxide and urea. This relies on a process called diffusion as there is no mixing of maternal and fetal blood in the placenta.