What Is the Placenta and What Does It Do?

Placenta use

General overview:

As well as growing a baby for nine months, your body has been busy growing another rather complicated structure – the placenta. The placenta is an organ that forms on the wall of your uterus and it both keeps your baby’s blood separate to your blood while also providing a link between the different blood supplies. This is so oxygen and nutrients can pass from you to your baby via the umbilical cord and also so waste products from your baby can pass back along the umbilical cord and into your bloodstream so you can dispose of them.

The placenta also makes hormones that help your baby develop and it also acts as a filter, preventing most types of bacteria as well as some toxins from reaching your baby. Towards the end of your pregnancy the placenta also transfers antibodies from your blood to your baby, with the resulting immunity lasting for around 3 months.

In the beginning:

After the 5–6 day old hatched blastocyst reaches your uterus, the outermost cells, called trophoblasts, make the first contact with and attachment to your uterine wall. This step is vitally important for implantation and consequently, a successful pregnancy. Once attached, the blastocyst burrows into your uterine lining, with the trophoblast cells invading into the deepest layers, making contact with your blood supply. The trophoblast cells form the outer layer of the placenta and your endometrium also contributes to the formation of the placenta. By the end of the first trimester (around 12 – 13 weeks), your blood supply is fully linked to the placenta and the placenta is functioning at full capacity.

Hormone production of the placenta:

The first hormone produced by the placenta is the hormone detected in pregnancy tests – human choriogonadotropin (hCG). This hormone tells your corpus luteum (a temporary cyst left over from ovulation) to keep producing estrogen and progesterone. If the corpus luteum doesn’t receive this signal, it will gradually disappear as will hormone production which then triggers menstruation.

Other important hormones made by the placenta once it is up and running at the end of the first trimester include progesterone, estrogen and one you may not have heard of before – human placental lactogen. Human placental lactogen helps develop your baby’s metabolism, aids in general growth and development and stimulates production of insulin and other important hormones.

Other important functions:

The placenta also helps your baby avoid attack from your immune system. One of the ways it does this is by making a substance that helps hide your baby from your immune system – phosphocholine molecules which contain something called neurokinin-B.

Another important feature of the placenta is the presence of a reservoir of blood which it can deliver to your baby if hypotension occurs.

Delivering the placenta:

The placenta is usually expelled within 30 minutes of giving birth and can be helped along with an intramuscular injection of oxytocin. Studies have found that this can help reduce blood loss as well as the risk of postpartum bleeding. As for what you choose to do with the placenta after it has been delivered that is up to you. Some cultures bury the placenta for various reasons, such as to emphasize the relationship between humans and the earth. The Kwakiutl in Canada bury girls’ placentas to give the girl skill in digging clams and bury the boys’ placentas to encourage prophetic visions. Or you might follow the current trend of eating your placenta, although maybe it might be a better idea just to have a nice juicy steak!

Melody Watson
Melody Watson holds Bachelors degrees in Biochemistry and Microbiology. She works as a medical writer for a medical communications agency in Berlin, Germany, where her work ranges from medical translation to writing publications for medical journals. Melody is passionate about promoting science, including evidence-based medicine, and debunking pseudoscience.

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