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Human reproduction
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Humans are mammals. A new baby starts when a sperm cell joins with an egg cell.
The reproductive systems
Male: the testes make sperm. Sperm travel along the sperm ducts and leave through the penis. Glands add fluid to make semen.
Female: the ovaries contain eggs. An egg travels along the oviduct (fallopian tube) to the uterus (womb). The cervix is a ring of muscle at the entrance to the uterus, which opens into the vagina.
Female: the ovaries contain eggs. An egg travels along the oviduct (fallopian tube) to the uterus (womb). The cervix is a ring of muscle at the entrance to the uterus, which opens into the vagina.
Gametes, the cycle and fertilisation
Sperm and egg cells are gametes (sex cells).
The menstrual cycle lasts about 28 days. About halfway through, an ovary releases an egg. If the egg is not fertilised, the uterus lining breaks down and leaves the body: this is a period.
Fertilisation is when a sperm nucleus joins with an egg nucleus. It happens in the oviduct.
The menstrual cycle lasts about 28 days. About halfway through, an ovary releases an egg. If the egg is not fertilised, the uterus lining breaks down and leaves the body: this is a period.
Fertilisation is when a sperm nucleus joins with an egg nucleus. It happens in the oviduct.
Gestation and birth
The fertilised egg divides and implants in the uterus lining. Gestation (pregnancy) lasts about 9 months.
The placenta lets oxygen and nutrients pass from the mother's blood to the foetus, and waste pass back. The umbilical cord joins the foetus to the placenta. Amniotic fluid cushions the foetus.
Harmful substances can also cross the placenta, so smoking, alcohol and some drugs can harm the foetus.
At birth, the muscles of the uterus contract and the cervix widens.
The placenta lets oxygen and nutrients pass from the mother's blood to the foetus, and waste pass back. The umbilical cord joins the foetus to the placenta. Amniotic fluid cushions the foetus.
Harmful substances can also cross the placenta, so smoking, alcohol and some drugs can harm the foetus.
At birth, the muscles of the uterus contract and the cervix widens.
Where does fertilisation happen, and what joins together?
- Sperm swim through the uterus into the oviduct.
- If an egg is there, one sperm can enter it.
- The two nuclei join.
Answer: In the oviduct: the nucleus of a sperm joins with the nucleus of an egg.
Testes make sperm; ovaries release eggs. Fertilisation happens in the oviduct. The foetus grows in the uterus for about 9 months, fed through the placenta, which harmful substances can also cross.
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