Pregnancy
Biology: Edexcel IGCSE, topic 4.1.11
Pregnancy
Pregnancy starts with fertilisation, when the nucleus of a sperm fuses with the nucleus of an egg, and involves many more stages:
Zygote
- Once an egg is fertilised by a sperm, it 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.
- The umbilical cord is a thick knot of blood vessels that connects the embryo and the placenta.
- An amniotic sac filled with amniotic fluid forms around the embryo to protect it from damage in the uterus.
Foetus
- 6 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
How many weeks after fertilisation is a human foetus fully formed?