Placental Function- (SPM Paper 2 2009)

• The placenta begins to form and grow during the first 4 weeks, due to the tissue of the embryo invading the wall of the uterus.
• The placenta is soft and has capillaries filled with the embryo’s blood.
• The wall of the uterus has large spaces filled with the mother’s blood. The wall of the placenta is very thin which brings the mother’s blood supply alongside the foetus to allow the exchange of food and oxygen to the foetus, and for the foetal waste and carbon dioxide to transfer to the mother.
• The blood of the mother and foetus do not mix, but substances are exchanged through the placenta by diffusion.
• The developing foetus does not breathe within the uterus, but instead it uses the placenta to get what it needs to develop and survive.

The placenta functions in ...
• metabolism,
• transport of substances and
• in endocrine secretion.

Metabolism:
• During early pregnancy, the placenta synthesizes glycogen, cholesterol and fatty acids, which serve as sources of nutrients and energy for the embryo and fetus.

Transport:
• The placenta has a very large surface area, which facilitates the transport of substances in both directions. The bulk of the substances transferred from mother to fetus consists of oxygen and nutrients.
• The fetus eliminates carbon dioxide and waste materials (eg., urea and bilirubin) into the maternal circulation.
• The exchange of gases occurs via diffusion.
• The placenta is also highly permeable to glucose,
• Amino acids are transported through speciic receptors.
• The transfer of maternal antibodies is important in providing passive immunity to the newborn.
• The placenta is also very permeable to alcohol and other drugs and to some viruses. These agents can cause birth defects.

Placental hormone synthesis:
i. Human chorionic gonadotropin (hCG):
• Synthesis of hCG begins before implantation, and is responsible for maintaining the maternal corpus luteum that secretes progesterone and estrogens.
• It is the basis for early pregnancy tests.
• Production peaks at eight weeks and then gradually declines.
ii.Estrogens and progesterone
• the placenta produces enough of these steroids to maintain the pregnancy and the corpus luteum is no longer needed.

The umbilical cord

• Oxygen and food materials in the mother’s blood diffuse across the placenta into the embryo’s blood and then carried along the umbilical cord to the embryo.
• Carbon dioxide and waste diffuse the other way and are carried away in the mother’s blood.
• The umbilical cord connects the baby to the mother’s placenta.
• The cord contains an artery, which carries waste products from the developing baby to the placenta,
• and a vein, which carries the food and oxygen to the foetus from the mother.

The amnion

A strong membrane called the amnion, which makes a fluid called amniotic fluid, protects the developing baby.
This helps to protect the foetus from being damaged by the mother during her normal activities over the nine months of development.


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