The Placenta's History and Mysteries

Have you ever wondered, "What is a placenta?" or "Where did it come from? or "How does it work?" Well, let me tell you it is quite an intriguing story.

To start things off, the placenta is an organ of the fetus (baby) that develops during pregnancy and attaches the growing fetus to the mother's uterine wall. This provides the baby with Oxygen & nutrients and removes waste from their blood via the mother's bloodstream. This development gave our ancestors an advantage over reptiles & other egg-laying species. Being able to carry their unborn young inside them eliminated having to abandon them in the face of danger and increased their youngs' survival rate.

The first mammal believed to possess this extraordinary organ was a small shrew-like creature known as Juramaia sinensis (The Jurassic Mother). One of, if not the first, fossil of this remarkable little mammal was discovered in Liaoning Province, China, by a team, including Ji Qiang of the Chinese Academy of Geological Science, in 2011. The Juramaia was dated to have lived around 160 million years ago, around the late Jurassic period. All known Eutherian (Placental) mammals are derived from this early mammalian ancestor.

As discovered by Tomoko & Fumitoshi Ishino, the gene responsible for the placenta's development is the PEG10 gene. Without this particular gene, the placenta does not fully form during the fetus' development. However, you might not know that the PEG10 gene is believed to have evolved from a retrovirus. This is because two sets of codes found in PEG10 are also expressed in a retrovirus. These virus genes are thought to have been inserted into our ancestor's DNA (Deoxyribonucleic Acid) & passed down to their descendants. Before the placenta revelation, our still egg-laying ancestors were attacked by a lethal retrovirus in the late Jurassic. This epidemic is thought to have nearly prompted the extinction of this monotreme (Egg-laying mammal) like ancestor. Survivors of this lethal virus underwent a dramatic evolutionary change as generations passed. After the virus DNA became one with that of our ancestors' reproductive cell chromosomes (what makes up DNA), this new DNA's integration caused a mutation, creating the PEG10 gene and forming the placenta. This allowed for a period of connection that helped ignite the maternal bond between mother & baby.

Over millions of years of evolution, the placenta's functions enhanced, & gestation periods grew longer—leading to the birth of comparatively mature young. During this long pregnancy, the placenta's primary function is to provide the fetus with Oxygen & nutrients while also removing waste from their blood. This occurs thanks to tree-like structures called Villous, which contain some of the baby's blood vessels. On the placenta's maternal side, openings connected to the mother's blood vessels feed the Villous a constant supply of vital gases & nutrients to the growing fetus. Much like the Bronchiole in our lungs.

Aside from this, the placenta's other primary function, and a typical retrovirus process. are suppressing the immune system. This is important because the fetus would otherwise be considered an invader to the mother's body, much like a virus, in the immune system's understanding. A common example of this misunderstanding is the child having a different blood type than their mom. To solve this, the placenta essentially makes the fetus invisible to the mother's body. This is done by the placenta acting as an immunosorbent (insoluble surfaces to which specific antibodies are attached to and removed...) sponge. It absorbs the bacteria/virus-fighting cells before they reach the unborn baby.

(Possibly, I couldn't actually find a super amount about how they do this exactly.)

Now some fun facts that are really out there, and you likely had no idea about.

To start, something you may or may not know, during labour & delivery, the placenta actually releases hormones throughout the body that increase maternal feelings. These include; Oxytocin (the love hormone), Beta-endorphins (hormone of pleasure & transcendence), Epinephrine & Norepinephrine (hormones of excitement) and Prolactin (The mothering hormone).

If you knew that already, nice! I honestly had no idea until I watched a documentary that mentioned it. However, I highly doubt that you'll know this next one.

Did you know, mosasaurs, a gigantic marine reptile alive around 145-66 million years ago, actually gave birth to live young?! Ya, and if you aren't already slack-jawed, get this. Small lizard ancestors, still living on land and semi-aquatic, also gave birth to live young! One particular ancestor was known as Aigialosauridae (Carsosaurs marchesetti). This long-time distant ancestor of common-day lizards and snakes had evolved, not only to live in water but to give live birth as well. They developed a placenta or a placenta-like organ around the same time as our ancient mammal ancestor. This, along with the ability to go into the water, significantly increased their offspring's survival rate.

Still not amazed? How about this; the mosasaurs have a living relative that inherited the viviparous lifestyle (having live young). This living relic is a small lizard is called Tiliqua rugosa, a.k.a, the Shingleback. Commonly found in Austalia, these omnivorous lizards are usually found sunning themselves in open areas.

Shinglebacks are very different from the mosasaur, more so similar to Marchetti, who still walked on land during the dinosaurs' rule. However, one thing they all had in common was the ability to have live young.

The Placenta!

Authour's notes:

Documentaies available on: Curiosity Stream

- Amazing Dinoworld: The World of Sea Monster

- Leaps in Evolution

- The Body: The Miracle Within

Few other fact sites:

- Britannica: Mosasaur

- CritterFacts: Shingleback

I am not sponsored by Curiosity Stream, though it is a good streaming app for interested people. I also want to apologize for not having super amounts of information about how the placenta functions. I really tried.