By Jeanne Garbarino, Biology Editor
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An historic view interpretation of the placenta (source). |
She gave me a few minutes to meet my daughter before she reeled me back into a state that was my new reality. “You’re not finished Jeanne. You still need to birth your placenta.” What?!?! More pushing? But I was lucky and the efforts required to bring my placenta ex vivo were minimal.
This is the second placenta my body helped make. OK, so it doesn't EXACTLY look like meatloaf... |
My first impression was that it
looked like “meatloaf.” Not necessarily
a well made meatloaf, but perhaps one that is made by my mother (sorry
mom). But, alas, chaos reigned and I
wasn’t able to really take a good look.
However, for my second birth and hence second placenta, my midwife indulged
me with a more detailed look and a mini-lesson.
Her gloved hands, still wet with my blood and amniotic fluid, slid into the opening that was artificially created with a tool resembling a crocheting needle. She opened the amniotic sac wide so I could get a baby's eye view of the crimson organ that served as a nutritional trading post between me and my new bundle of joy.
Baby's eye view: Where geekling deux spent 39 weeks and 4 days. |
She explained that the word
“placenta” comes from from the Greek word plakoeis,
which translates to “flat cake” (however, I’m sure if my mom’s meatloaf was
more common in ancient Greece, the placenta would be named differently). “It’s one of the defining features of being a
mammal,” she explained as I was working on another mammalian trait – getting my
baby to nurse for the first time.
That was about all I could
mentally digest at the time, but still, more than three years later, the placenta
continues to fascinate me, mostly due to the fact that it is responsible for
growing new life. It’s a natural topic
for this long overdue Pregnancy101
post, so let’s dive in!
Development of the placenta
It all starts when a fertilized
egg implants itself into the wall of the uterus. But, in order to fully understand how it
works, we should start with an overview of the newly formed embryo.
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The very early stages of us (and many other things that are alive). |
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The trophoblast invades the uterus, leading to implantation of the blastocyst. |
The act of implantation is largely due to the cells found on the perimeter of the blastocyst sphere. These cells, collectively known as the trophoblast, release a very important hormone – human chorionic gonadotropin (hCG) – that tells the uterus to prepare for it’s new tenant. (If you recall, hCG is the hormone picked up by pregnancy tests.) Around day 7, the trophoblast cells start to invade the lining of the uterus, and begin to form the placenta. It is at this point that pregnancy officially begins. (Here is a cool video, created by the UNSW Embryology Department, showing the process of implantation.)
Structure of the placenta
Structure of the placenta
Eventually the trophoblast
becomes the recognizable organ that is the placenta. Consider the “flat cake” analogy, with the
top of the cake being the fetal side (the side that is in contact with the
baby), and the bottom of the cake being the maternal side (the side that is in
contact with the mother).
umbilical cord serves as
the tunnel through which nutrients and waste are shuttled, and essentially
serves to plug the baby into the mother’s metabolic processes. At the umbilical cord-placenta nexus, the
umbilical cord arteries and vein branch out into a network of blood vessels, which further
divide into a tree-like mass of vessels within the placenta.
These tree-like masses
originating from the umbilical cord (and thus fetus) sit in a cavity called
the intervillous space, and are bathed in nutrient-rich maternal blood. This maternal blood, which provides the fetus
with a means for both nutrient delivery and waste elimination, is continually
replenished via a network of maternal arteries and veins that feed into the
intervillous space. Furthermore, these arteries and veins help to anchor the placenta into the uterine wall. One of the most interesting aspects about the mother-feus relationship is that the blood vessel connection is indirect. This helps to prevent a detrimental immune response, which could lead to immunological rejection of the fetus (sort of like how a transplanted organ can become rejected by the recipient).
Functions of the placenta
Just like a plant needs
sunlight, oxygen, and water to grow, a baby needs all sorts of nutrients to
develop. And since a baby also produces
waste, by nature of it being alive and all, there is an absolute requirement
for waste removal. However, because we
can’t just give a developing fetus food or a bottle, nor are we able to change
diapers in utero, the onus lies
completely on the biological mother.
This is where the placenta comes
in. Because the fetus is plugged into the circulatory system of the mother via
the umbilical cord and placenta, the fetus is provided with necessary nutrients
and a mechanism to get rid of all the byproducts of metabolism. Essentially, the placenta acts as a waitress
of sorts – providing the food, and cleaning it all up when the fetus is done
eating.
But it’s not just about
nutrition and waste. The placenta also
serves as a hormone factory, making and secreting biological chemicals to help
sustain the pregnancy. I mentioned above
that the placenta produces hCG, which pretty much serves as a master regulator
for pregnancy in that it helps control the production of maternally produced
hormones, estrogen and progesterone. It
also helps to suppress the mother’s immunological response to the placenta
(along with other factors), which cloaks the growing baby, thereby hiding it
from being viewed as a “foreign” invader (like a virus or bacteria).
Another hormone produced by the
placenta is human placental lactogen (hPL), which tells the mother to increase
her mammary tissue. This helps mom
prepare for nursing her baby once it’s born, and is the primary reason why our
boobs tend to get bigger when we are pregnant.
(Yay for big boobies, but my question is, what the hell transforms our
rear ends into giant double cheeseburgers, and what biological purpose does
that serve?? But I digress…)
Despite the fact that the mother's circulatory system remains separate from the baby's circulatory system, there are a clear mixing of metabolic products (nutrients, waste, hormones, etc). In essence, if it is in mom's blood stream, it will very likely pass into baby's blood stream. This is the very reason that pregnant mothers are strongly advised to stay away from cigarettes, drugs, alcohol, and other toxic chemicals, all of which can easily pass through the placental barrier lying between mother and fetus. When moms do not heed this warning, the consequences can be devastating to the developing fetus, potentially leading to birth defects or even miscarriage.
Despite the fact that the mother's circulatory system remains separate from the baby's circulatory system, there are a clear mixing of metabolic products (nutrients, waste, hormones, etc). In essence, if it is in mom's blood stream, it will very likely pass into baby's blood stream. This is the very reason that pregnant mothers are strongly advised to stay away from cigarettes, drugs, alcohol, and other toxic chemicals, all of which can easily pass through the placental barrier lying between mother and fetus. When moms do not heed this warning, the consequences can be devastating to the developing fetus, potentially leading to birth defects or even miscarriage.
There are also situations that
could compromise the functions of the placenta – restriction of blood supply,
loss of placental tissue, muted placental growth, just to name a few – reducing the
chances of getting and/or staying pregnant. This placental
insufficiency is generally accompanied by slow growth of the uterus, low
rate of weight gain, and most importantly, reduced fetal growth.
And it’s not just the growth of the
placenta that is important – where the placenta attaches to the uterus is also
very important. When the placenta grows
on top of the opening of the birth canal, the chances for a normal, vaginal
birth are obliterated. This condition,
known as placenta
previa, is actually quite dangerous and can cuase severe bleeding in the
third trimester. 0.5% of all women
experience this, and it is one of the true medical conditions that absolutely
requires a C-section.
Then, there is the issue of
attachment. If the placenta doesn’t
attach well to the uterus, it could end up peeling away from the uterine wall,
which can cause vaginal bleeding, as well as deprive the baby from nutrient
delivery and waste disposal. This abruption of the
placenta is complicated by the use
of drugs, smoking, blood clotting disorders, high blood pressure, or if the
mother has diabetes or a history of placental abruption.
Conversely, there are times when
the blood vessels originating from the placenta implant too deeply into the
uterus, which can lead to a placenta
accreta. If this occurs, the mother
generally delivers via C-section, followed by a complete hysterectomy.
Cultural norms and the placenta
There are many instances where
the placenta plays a huge role in the culture of a society. For instance, both the Maori people of New
Zealand and the Navajo
people of Southwestern US will bury the placenta. There is also some folklore associated with
the placenta, and several societies believe that it is alive, pehaps serving as
a friend for the baby. But the
tradition that seems to be making it’s way into the granola culture of the US
is one that can be traced back to traditional Chinese practices: eating the
placenta.
Placentophagy, or eating
one’s own placenta, is very common among a variety of mammalian species. Biologically speaking, it is thought that
animals that eat their own placenta do so to hide fresh births from predators,
thereby increasing the chances of their babies’ survival. Others have suggested that eating the
nutrient-rich placenta helps mothers to recover after giving birth.
However, these days, a growing
number of new mothers are opting to ingest that which left their own body
(likely) through their own vaginas. And
they are doing so though a very expensive process involving dehydrating and encapsulating
placental tissue.
Why would one go through this
process? The claims are that
placentophagy will help ward of post partum depression, increase the supply of
milk in a lactating mother, and even slow down the ageing process. But, alas, these are some pretty bold claims
that are substantiated only by anecdata, and not actual science (see
this).
So, even though my placentas
looked like meatloaf, there was no way I was eating them. If you are considering this, I’d approach the
issue with great skepticism. There are
many a people who will take advantage of maternal vulnerabilities in the name
of cold hard cash. And, always remember,
if the claims sound to good to be true, they probably are!
Thanks for tuning into this issue of Pregnancy101, and enjoy this hat, and a video!
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Awesome post, Jeanne. I love the placenta, but I had no interest in eating my own. One of the things that I find most interesting about the placenta is how much variation there is between animal species in microscopic structure. Some species - ruminants, pigs, horses - have a full 2 intact epithelial membranes separating mom and baby's blood. In these species, fewer nutrients and immunoglobulins cross the placenta, so their young are born pretty lean and really need colostrum fast to get their immune systems going. We humans have a much more intimate placental structure, and nutrients and immunoglobulins (as well as more unsavory compounds, as you mention) pass easily from mom to baby.
ReplyDeleteGreat article, but it's not correct to say the placenta is the only organ to completely form after birth, as it's made entirely of the baby's cells, and therefore forms before birth.
ReplyDeleteThe placenta consists of maternal and fetal components, see e.g., http://embryology.med.unsw.edu.au/notes/placenta8.htm
ReplyDelete