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Science

Reproduction

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Fertilisation and foetal development

Fertilisation

During sexual intercourse the man's penis releases semen into the woman's vagina. Sperm cells travel in semen from the penis and into the top of the vagina. They enter the uterus through the cervix and travel to the egg tubes. If a sperm cell meets with an egg cell there, fertilisation can happen. Fertilisation happens when an egg cell meets with a sperm cell and joins with it.

The fertilised egg divides to form a ball of cells called an embryo. This attaches to the lining of the uterus and begins to develop into a foetus (pronounced "fee-tuss") and finally a baby.

Development of the foetus

The foetus relies upon its mother as it develops. These are some of the things it needs:

  • protection

  • oxygen

  • nutrients (food and water).

It also needs its waste substances removing.

The foetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amnion.

The placenta is responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the foetus by the umbilical cord.

The mother's blood does not mix with the foetus's blood, but the placenta lets substances pass between the two blood supplies:

  • oxygen and nutrients diffuse across the placenta from the mother to the foetus

  • waste substances, such as carbon dioxide, diffuse across the placenta from the foetus to the mother.

Birth

After nine months the baby is ready to be born. The cervix relaxes and muscles in the wall of the uterus contract, pushing the baby out of the mother's body.

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