Role of the Placenta (Edexcel IGCSE Biology (Modular))

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

  • In the placenta the mother’s blood comes into very close proximity to the blood of the fetus

  • The umbilical cord connects the embryo’s 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, e.g. glucose, amino acids 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 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