Role of the Placenta (Edexcel IGCSE Biology): Revision Note

The Placenta

• After fertilisation in the oviduct the zygote divides to form an embryo, and travels to the uterus

• Upon reaching the uterus the embryo implants in the uterine lining, where it continues to develop

• A structure called the placenta forms at the implantation site

• The placenta provides the developing embryo with nutrients and oxygen from the mother’s blood, which are essential for growth and development

• It also allows waste products from the embryo’s blood to be removed

• In the placenta, the mother’s blood comes into very close proximity to the blood of the fetus, but the two blood supplies do not mix

• The umbilical cord connects the fetus’ blood supply to the placenta

• The role of the placenta is to enable exchange of substances between the mother's blood and that of the fetus

• Substances that travel from the mother's blood to the fetus include:

  • Oxygen

  • Nutrients, eg. glucose, amino acids, vitamins and mineral (ions)

• Substances that travel from the fetus' blood to the mother include:

  • Carbon dioxide

  • Urea

• The placenta is an efficient exchange surface because it has:

  • A large surface area

  • A thin wall for efficient diffusion

• The placenta also acts as a barrier to some toxins and pathogens, although not all are stopped from passing through. For example:

  • Nicotine and alcohol can pass across the placenta

  • Virus particles can pass across the barrier

The placenta allows exchange of substances between the fetus and the mother