Pregnancy
Science: KS3, topic 1.2.5
Pregnancy
Pregnancy starts with fertilisation. Fertilisation is when the nucleus of a sperm fuses with the nucleus of an egg. Pregnancy involves many more stages:
Zygote
- An egg fertilised by a sperm is called a zygote.
- The zygote cell then starts to divide to form a ball of cells.
Embryo
- Once a ball of cells has formed, this is called an embryo.
- The embryo then implants itself into the wall of the uterus.
Placenta
- Once the embryo has implanted, various structures form to connect the embryo to its mother:
- A placenta forms between the embryo and the wall of the uterus.
Cord and amniotic sac
- The umbilical cord is a thick knot of blood vessels connecting the embryo and the placenta.
- An amniotic sac filled with amniotic fluid surrounds the embryo to protect it from damage in the uterus.
Foetus
- 8 weeks after fertilisation, the embryo can be called a foetus.
- The foetus continues to grow and become more complex.
- The baby is fully formed at around 38 to 40 weeks.
Test yourself on Pregnancy
Pregnancy
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How many weeks after fertilisation can an embryo be called a foetus?