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Placenta - What Is It and How It Works

Placenta Definition

The placenta is an organ which is responsible for nourishing and protecting a fetus during pregnancy. It is unique in that it is a temporary organ; it grows alongside the fetus during pregnancy, and then is expelled along with the fetus at birth. The placenta is also sometimes called “afterbirth,” as it is expelled through the vagina after the fetus has been delivered.

The placenta performs myriad functions to support fetal development, including facilitating blood flow, gas exchange, waste elimination, and serving as a protective barrier for the fetus against any infections the mother experiences during pregnancy.

The placenta is unique in that it is an organ which arises from the tissue of two genetically distinct organisms; part of the placenta develops from the tissue of the mother’s uterine wall, while another part develops from the fetus’ own tissue. After the blastocyst which will develop into the fetus makes contact with the uterine wall, blastocyst and maternal tissue grow together to form a single, cooperating organ that links the two together.

Mammals who give birth to live, fully-developed young, rather than laying eggs or carrying underdeveloped offspring in pouches, are often called “placental mammals.” The evolution of the placenta is one of the primary characteristics shared by all mammals except for marsupials and egg-laying mammals such as the platypus.

Some marsupials – close cousins to placental mammals like cats, dogs, and humans – have a primitive placenta in which blood vessels grow throughout the protective membranes surrounding the embryo. It is possible that placentas as we know them may have evolved from similar primitive structures in found the common ancestor of marsupials and placental mammals.

Pregnancies in which the placenta does not develop properly typically miscarry. This can occur either because of problems with the development of maternal uterine tissue, or because of problems with development of the fetal placental tissue. Fetuses which suffer from chromosomal problems may not be able to form a proper placenta and may miscarry, most often in the first trimester.

Many animals and some human cultures make a practice of eating the placenta after it is delivered. Scientists are divided on whether this is a good idea for humans. Some say it may contain valuable nutrients and even hormonal components that can be of assistance to the mother after pregnancy; others say that this practice may carry a risk of spreading infectious diseases, and that no benefits to eating the placenta have been proven in humans.

Function of Placenta

The placenta acts as a lifeline between the mother and fetus, ensuring that the fetus gets what it needs from the mother’s body to survive. At the same time, it acts as a protective barrier, shielding the fetus from some maternal infections. The functions of the placenta include:

• Allows gas exchange so the fetus gets enough oxygen
• Helps the fetus get sufficient nutrition
• Helps regulate the fetus’ body temperature
• Removes waste from the fetus for processing by the mother’s body
• Filters out some microbes that could cause infection
• Transfers antibodies from the mother to the fetus, conferring some immune protection
• Produces hormones that keep the mother’s body primed to support pregnancy

The placenta, then, essentially serves the function of several organ systems for the fetus, since the fetus is unable to eat, breathe, or eliminate waste itself while it is inside the womb!

Unfortunately, the placenta is not fool-proof as an infection barrier, and some fetuses do become infected with diseases contracted by their mother. Toxins of sufficiently small molecular size can also pass through.

That’s one reason why pregnant women are advised to avoid all possible sources of disease and toxins – diseases and toxins which may not be dangerous at all to adult women may be devastating to a developing fetus.

How Does the Placenta Work

When it is delivered, the placenta looks like a flat, round organ that is suffused with thick blood vessels. The fetus’ umbilical cord attaches to one flat surface, while the reverse surface grows out of the mother’s uterus during pregnancy.

The placenta works mainly by allowing substances to be exchanged between maternal and fetal blood. This allows the fetus to obtain nutrients, oxygen, antibodies, and other vital substances without having to share the mother’s blood supply directly.

This is vital because fetuses do not always have the same blood type as their mother, and direct mixing of the bloodstreams could cause the mother’s immune system to attack the fetal blood supply. Even with the placenta separating the two, problems are occasionally caused by maternal antibodies attacking fetal blood supplies. Some women receive vaccines or other treatments to stop that form happening.

The diagram below shows how the fetal blood vessels infiltrate the placenta. It also shows how the mother’s arteries permeate the placenta. The placental tissue in between the two acts as a sort of filtration system, preventing most cells from passing through the barrier while allowing substances such as nutrients, antibodies, and gases to do so:

Eating the Placenta

In recent years, the topic of placenta-eating has been in the news a great deal. Many celebrities have contracted with companies that promise to turn their placentas into pills or food, and touted it as a move that has great health benefits. But many doctors have cautioned that there’s no evidence that placenta-eating confers real health benefits, and that eating your placenta may actually make your baby’s health worse.

In nature, animals often eat their placentas. There’s good reason for this: in nature food is often scarce, and the placenta is rich in protein, iron, and other nutrients that can be difficult to procure in the wild. That means that placenta-eating is often worth the risk for animal moms who just gave birth, and now need to provide nutritious milk for their young.

However, for humans, the risk of disease may outweigh any benefits of placenta-eating. Because the placenta serves as a filter to prevent harmful bacteria and viruses from reaching the baby, it can contain bacteria from infections the mother had during pregnancy.

Even if these pathogens aren’t harmful to the mother – some viruses and bacteria hardly bother adults – they can still be passed on to the newborn baby through breast milk, if the mother consumes an infected placenta. Cases have been recorded of babies becoming sick with bacterial infections which were later traced to their mother’s placenta supplements.

For that reason, many doctors counsel that the placenta is just like any other human tissue – it should not be eaten by humans, because doing so could spread disease.

Because the placenta does not qualify as a medication, health food and birthing companies that promise a “healthy experience” if you pay them to prepare your placenta are often not subject to the same regulations for safety and effectiveness as medications are.

In conclusion, just because some famous moms have done it doesn’t mean it’s a scientifically supported idea!

Quiz

1. Why are mammals such as dogs, cats, and humans called “placental mammals?”
A. Because the placenta is the evolutionary adaptation we all share, while monotremes, marsupials, and non-mammals do not.
B. Because all placental mammals have placentas, while only some non-mammals have placentas.
C. Both of the above.

Answer to Question #1

A is correct. Only placental mammals have fully developed placentas, while non-mammals and older mammal lineages such as monotremes and marsupials do not.

2. Which of the following is true of the placental filtration system?
A. It is able to filter out all diseases and toxins, protecting the fetus.
B. It allows nutrients and oxygen to pass through, nourishing the fetus.
C. It is able to filter out some diseases and toxins, but not all of them.
D. Both B and C.

Answer to Question #2

D is correct. The placenta allows nutrients, oxygen, and other beneficial substances to pass from the mother to the fetus. It screens out some bacteria and toxins, but is unfortunately not able to screen out all of them. That’s why pregnant women are counseled to avoid potential sources of toxins and disease.

3. Which of the following is NOT true of placental anatomy?
A. It contains many blood vessels from both the mother and fetus.
B. It is composed of both maternal and fetal tissue.
C. It allows the mother’s blood to flow into the fetus, nourishing it.
D. None of the above.

Answer to Question #3

C is correct. The placenta separates the maternal and fetal blood supplies, to prevent the mother’s immune system from attacking fetal blood cells. However, it does allow some substances such as nutrients, gases, and antibodies to be exchanged.

References

• Slater, D. (2017, April 03). The Myth Of The Placental Barrier. Retrieved July 08, 2017, from https://www.fitpregnancy.com/pregnancy/pregnancy-health/myth-placental-barrier
• 10.2 Development of the placental villi. (n.d.). Retrieved July 08, 2017, from http://www.embryology.ch/anglais/fplacenta/villosite01.html
• Should I Eat My Placenta? (n.d.). Retrieved July 08, 2017, from http://www. webmd.com/baby/should-i-eat-my-placenta

Maternity hospital №7, Novosibirsk - What is the placenta?

Anna Valentinovna Yakimova, obstetrician-gynecologist, MD talks about the placenta and placental insufficiency.

Picture from the site http://s7ya7.zdorovo-zivi.ru

Placenta. The name of the organ comes from lat. placenta - cake, cake, pancake. This is an extra-embryonic organ, consisting of villi, thanks to which the fetus is nourished, respired, and waste products are removed from its blood. There are free and fixing (anchor) villi. The placenta is formed in the place where the embryo was implanted, arises as a result of the connection of the chorion - extraembryonic tissue with a thickened uterine mucosa (decidual tissue). Despite the fact that the blood of the mother and fetus does not mix, as they are separated by the placental barrier, the fetus receives all the necessary nutrients and oxygen from the mother's blood. In addition, the placenta produces hormones that ensure the preservation of pregnancy. The placenta has two surfaces. The surface that faces the fetus is called the fetal. It is covered with a smooth shell - the amnion, through which large vessels shine through. The one that is attached to the wall of the uterus is called maternal.

The main structural unit of the placenta is cotelidone. Cotyledon of the placenta is conditionally comparable to a tree. Each cotyledon is formed by a stem villus, from which, like branches of a tree, villi of the second and third order extend, containing vessels. The central part of the cotyledon forms a cavity, which is surrounded by many villi. Between the cotyledons there is a space - mejvirus, which on the maternal side is limited by partitions (septa) extending from the mucous membrane of the uterus. Most of the placental villi are freely immersed in the intervillous space (free villi) and are bathed in maternal blood. The spiral arteries, which are small branches of the arteries that supply the uterus, open into the intervillous space and supply oxygen-rich blood to the intervillous space. Due to the pressure difference, which is higher in the mother's arterial bed compared to the intervillous space, oxygenated blood from the mouths of the spiral arteries is directed through the center of the cotyledon to the villi, washes them, reaches the chorionic plate and returns to the maternal circulation through the venous orifices through the separating septa. . In this case, the blood flow of the mother and fetus are separated from each other. Those. maternal and fetal blood does not mix. Thus, the concept of the placental barrier appears: the blood of the mother of the fetus does not mix, because they are separated by the wall of the villus, loose connective tissue inside the villus and the wall of the vessel that is inside the villus, and in which the blood of the fetus circulates.

At the end of pregnancy, the placenta is a soft disk 15-18 cm in diameter, 2-4 cm thick in the central part, weighing about 500-600 g. their capillaries - 12 m2. The placenta, membranes, and umbilical cord together form the afterbirth, which is expelled from the uterus after the baby is born.

Normally, the placenta is attached to the uterine cavity on its anterior or posterior surface, sometimes in the fundus. If the placenta is attached in the lower part of the uterine cavity, close to the internal opening of the cervix - the internal pharynx, then its blood supply is often insufficient and the fetus may suffer from lack of oxygen and nutrients - a phenomenon called placental insufficiency occurs.

Placental insufficiency is a violation of all or some of the functions of the placenta, ultimately leading to oxygen starvation (hypoxia), fetal growth retardation or death and / or early termination of pregnancy.

Placental insufficiency may occur early in pregnancy due to impaired placental formation, for example, if the spiral arteries that supply blood to the villi do not lose the ability to narrow their lumen in response to exposure to vasoconstrictor substances. It is possible that there is a violation of the development of blood vessels inside the villi, the vessels can form in the central part of the villus, and not close to its wall, then the transfer of nutrients from the mother's blood to the fetal blood and the flow of metabolic products back will be difficult. The process of development of the placenta (in particular, vascular formation) occurs to a greater extent in the first and second trimesters of pregnancy, ending at about 30-32 weeks. After this period, involutive processes predominate ("aging", immuring the villi with fibrinoid). Along with the processes of involution in the placenta during pregnancy, young villi develop, more often avascular, which, however, only partially compensate for the function of mature villi containing vessels that have “fallen out” of the circulation.

In another scenario, placental insufficiency occurs at a later date, as a result of damage to the placenta in inflammatory processes, diabetes in a pregnant woman, or high blood pressure, when blood flow to the uterus is disturbed, which can also occur with increased maternal blood clotting . It is believed that it is the violation of the uteroplacental circulation that plays the main role in the formation of the intrauterine growth retardation syndrome. Before the advent of Doppler ultrasound research methods in obstetric practice, there were no non-invasive methods for studying blood flow in the mother-placenta-fetus system. To date, Doppler is the most preferred instrumental method that provides useful information in relation to the detection of blood flow disorders and the determination of pregnancy management tactics for placental insufficiency. If there are symptoms of placental insufficiency - a mismatch in the height of the uterine fundus, signs of a threat of early termination of pregnancy, rapid or slow fetal heart rate (normal: 120-160 beats per minute), an altered amount of amniotic fluid - it is necessary to conduct an ultrasound examination, Doppler blood flow in the vessels of the uterus, umbilical cord and fetus, and in the third trimester - cardiotocography. The earliest sign of placental dysfunction is a decrease in its production of hormones and proteins, therefore, in pregnant women with a known risk of placental dysfunction (for example, if she has a chronic inflammatory process or often / constantly increased blood pressure, etc. ), you can examine the level placental lactogen, progesterone, unconjugated estriol in the blood. And on the basis of the data obtained, predict the further development of pregnancy and take preventive measures.

Can placental insufficiency be treated? The answer to this question is ambiguous. It is possible to influence the development of the placenta when it is incomplete, improving the conditions for development - by eliminating, for example, the inflammatory process, normalizing blood pressure, lowering the tone of the uterus, and normalizing blood clotting. You can influence the metabolism in the cells of the placenta - by doing this, for example, by introducing drugs into the body of a pregnant woman that help improve the utilization of glucose by cells. It is possible to influence the tone of the vessels, reduce the permeability of the wall and, in this way, the swelling of the tissues decreases and the penetration of oxygen into them improves. But we must understand that we do not cure placental insufficiency, we are only trying to influence the compensatory mechanisms that exist in the placenta, if this succeeds, the manifestations of placental insufficiency disappear. But more often, treatment is aimed at prolonging the pregnancy to the term of a viable fetus.

But if the signs of placental insufficiency increase, and the gestation period is more than 32 weeks, when even in a normal placenta it undergoes involution, the placenta initially developed incorrectly, and now it performs its functions worse, the fetus suffers, then it is useless to treat placental insufficiency, it is better to carry out early delivery and to nurse the newborn without the risk of intrauterine death, which is possible if the placenta depletes its reserves. Sometimes it is necessary to make a decision on early delivery and at an earlier date, when the treatment of placental insufficiency is impossible and the delay threatens the life of the fetus.

What is the placenta

It connects two organisms - the mother and the fetus, providing it with the necessary nutrients.

Where is the placenta located and what does it look like?

In a normal pregnancy, the placenta is located in the body of the uterus along its posterior (more often) or anterior wall. It is fully formed by the 15-16th week of pregnancy, after the 20th week, active exchange begins through the placental vessels. From the 22nd to the 36th week of pregnancy, an increase in the mass of the placenta occurs, and by the 36th week it reaches full functional maturity.

In appearance, the placenta looks like a round flat disk. By the time of delivery, the weight of the placenta is 500-600 g, the diameter is 15-18 cm and the thickness is 2-3 cm.

Functions of the placenta

• First, gas exchange occurs through the placenta: oxygen penetrates from the mother's blood to the fetus, and carbon dioxide is transported in the opposite direction.
• Secondly, the fetus receives through the placenta the nutrients necessary for its growth and development. It must be remembered that many substances (alcohol, nicotine, drugs, many drugs, viruses) easily penetrate through it and can have a damaging effect on the fetus. In addition, with its help, the fetus gets rid of the products of its vital activity.
• Thirdly, the placenta provides immunological protection to the fetus, delaying the cells of the mother's immune system, which, having penetrated to the fetus and recognized a foreign object in it, could trigger its rejection reactions. At the same time, the placenta passes maternal antibodies that protect the fetus from infections.
• Fourthly, the placenta plays the role of an endocrine gland and synthesizes hormones (human chorionic gonadotropin (hCG), placental lactogen, prolactin, etc.) necessary to maintain pregnancy, growth and development of the fetus.

Normally, the placenta together with the membranes (afterbirth) is born 10-15 minutes after the birth of the fetus. She is carefully examined and sent for a morphological study. First, it is very important to make sure that the whole placenta was born (that is, there are no damages on its surface and there is no reason to believe that pieces of the placenta remained in the uterine cavity). Secondly, according to the state of the placenta, one can judge the course of pregnancy (whether there was an abruption, infectious processes, etc.).

What do doctors want to know about the placenta?

During pregnancy, it is important to look for signs of placental dysfunction - placental insufficiency. To do this, during an ultrasound study, the structure of the placenta, its location in the uterine cavity, thickness, and the correspondence of the size of the fetus to the gestational age are studied. In addition, the blood flow in the placental vessels is studied.

Degree of maturity

This parameter, as doctors say, is "ultrasonic", that is, it depends on the density of the structures of the placenta determined by ultrasound.

There are four degrees of placental maturity:

• Normally, zero degree of placental maturity should be determined before 30 weeks of pregnancy.
• The first degree is considered valid from 27 to 34 weeks.
• Second - from 34 to 39.
• Starting from 37 weeks, the third degree of placental maturity can be determined.

At the end of pregnancy, the so-called physiological aging of the placenta occurs, accompanied by a decrease in the area of ​​its exchange surface, the appearance of areas of salt deposition.

Place of attachment

Determined by ultrasound. As mentioned above, during a normal pregnancy, the placenta is located in the body of the uterus. Sometimes, during an ultrasound examination in the first half of pregnancy, it is found that the placenta is located in the lower parts of the uterus, reaching or even overlapping the area of ​​​​the internal os of the cervix. In the future, as pregnancy progresses, the placenta most often shifts from the lower sections of the uterus to the top. However, if after 32 weeks the placenta still overlaps the area of ​​the internal os, this condition is called *placenta previa**, which is a serious complication of pregnancy.

Placenta previa can lead to bleeding, which can occur during the second or third trimester of pregnancy or during childbirth.

Thickness

Also determined by ultrasound - placentometry: after establishing the placenta attachment, the area where it has the largest size is found, which is determined. The thickness of the placenta, as already mentioned, continuously increases until 36-37 weeks of pregnancy (by this time it ranges from 20 to 40 mm). Then its growth stops, and in the future the thickness of the placenta either decreases or remains at the same level.

Deviation from the norm of at least one of these indicators may indicate trouble during pregnancy.

References

• Tiwari D., Das CR., Sultana R., Kashyap N., Islam M., Bose PD., Saikia AK., Bose S. Increased homocysteine ​​mediated oxidative stress as a key determinant of hepatitis E virus ( HEV) infected pregnancy complication and outcome: A study from Northeast India. // Infect Genet Evol - 2021 - Vol - NNULL - p.104882; PMID:33905889
• Salmanian B., Belfort M.A., Shamshirsaz A.A. The risk of placenta accreta spectrum in women with in vitro fertilization in different populations. // Am J Obstet Gynecol - 2021 - Vol - NNULL - p.; PMID:33905744
• Olmos-Ortiz A., Olivares-Huerta A., García-Quiroz J., Zariñán T., Chavira R., Zaga-Clavellina V., Avila E., Halhali A., Durand M., Larrea F., Díaz L. Placentas associated with female neonates from pregnancies complicated by urinary-tract infections have higher cAMP content and cytokines expression than males. // Am J Reprod Immunol - 2021 - Vol - NNULL - p.e13434; PMID:33905581
• Tandl V., Hoch D., Bandres-Meriz J., Nikodijevic S., Desoye G., Majali-Martinez A. Different regulation of IRE1α and eIF2α pathways by oxygen and insulin in ACH-3P trophoblast model. // Reproduction - 2021 - Vol - NNULL - p.; PMID:33904834
• Ji S., Gumina D., McPeak K., Moldovan R., Post MD. , Su EJ. Human placental villous stromal extracellular matrix regulates fetoplacental angiogenesis in severe fetal growth restriction. // Clin Sci (Lond) - 2021 - Vol - NNULL - p.; PMID:33904582
• Shmeleva EV., Colucci F. Maternal natural killer cells at the intersection between reproduction and mucosal immunity. // Mucosal Immunol - 2021 - Vol - NNULL - p.; PMID:33903735
• Moreno-Sepulveda J., Espinós JJ., Checa MA. Lower risk of adverse perinatal outcomes in natural versus artificial frozen-thawed embryo transfer cycles: a systematic review and meta-analysis. // Reprod Biomed Online - 2021 - Vol - NNULL - p.; PMID:33903031
• Owen M.D., Cassidy A.L., Weeks AD. Why are women still dying from obstetric hemorrhage? A narrative review of perspectives from high and low resource settings. // Int J Obstet Anesth - 2021 - Vol - NNULL - p.102982; PMID:33903002
• Liu CN., Yu FB., Xu YZ., Li JS., Guan ZH., Sun MN., Liu CA., He F., Chen DJ. Prevalence and risk factors of severe postpartum hemorrhage: a retrospective cohort study.

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