What is the function of the placenta? How does the placenta work? What happens to the placenta after birth? These should be important questions for any future mother if she wants to have complete control over her pregnancy.
Table of Contents
What Is a Placenta and What Does It Do?
The placenta is a temporary organ which develops in the uterus and helps the baby receiving all the necessary nutrients to develop during the 40 weeks of pregnancy. At 12 weeks of pregnancy, the placenta is completely formed. The placenta has the shape of a disc at delivery, measures around 18 to 20 cm in diameter and only a little over 5 cm in thickness. Its upper part is completely smooth and the hip which adheres to the wall of the uterus is rough. The placenta is richly vascularized. The umbilical cord is the one connecting the placenta to the baby.
Progesterone, estrogen and hCG are produced by the placenta. The placenta is the organ responsible for functioning as a trading post between blood supply of the mother and baby. There are tiny blood vessels that carry fetal blood through this organ, which is already full of maternal blood. Oxygen and nutrients from the blood of the mother are transferred to the baby`s blood, while in turn waste products are transferred from baby`s blood to the maternal blood, without the 2 blood supplies ever mixing. – Read more!
The placental membrane divides the 2 circulations:
- The maternal placental circulation which runs from the basal plate.
- The villous fetal circulation which runs in a capillary system with an arterial path and a venous one.
The placenta is removed from the mother`s uterus in a process known as the after-birth process. A potential issue during pregnancy is placenta praevia, when the placenta gets attached over the cervix. As the baby develops, bleeding may occur due to the pressure caused on the placenta. This medical condition needs medical assistance to make sure labor and delivery run safely for both the mother and baby.
Transporting Function of the Placenta
Transfer of Some Important Elements
- Oxygen – The transfer of the oxygen is made through the mechanism of simple diffusion. The consumption of oxygen of the uterus and its content at term is of around 20ml/min. from which 2/3 transferred to the fetus.
The fetus has a great ability of maintaining the consumption of oxygen. The fetal hemoglobin presents an affinity for oxygen, and if the umbilical flow is reduced, the fetus has an increased ability of extracting the oxygen. In case that the released of the oxygen towards the fetus is reduced, the most part from the umbilical venous blood is diverted towards myocardium and the upper side of the heart. The secretion of catecholamines will increase simultaneously along with the achievement of vasoconstriction.
- Carbon Dioxide – At the placental membrane`s level, the permeability to carbon dioxide is increased.
- Water – The water flow at the placental level is influenced by the osmotic and hydrostatic force as well as the electrolyte gradient, the fetus drinking a large quantity of water on a daily basis.
- Glucose – The main energy substrate for the fetus is formed from maternal glucose. The normal transfer of this nutrient is an essential condition for the normal development of the fetus, so at the term, the placental transfer must be of around 20mg/min, around 30g/day. The main way of the transfer is the facilitated diffusion made through certain proteins. The placenta is also big consumer of glucose, and the rate of the transfer is influenced by this aspect as well.
- Amino Acids – The fetal protein synthesis starts from the transferred amino acids through the placenta and present in the fetal plasma in higher concentrations than the maternal one. – More info!
- Proteins – The placenta is impermeable at proteins, but there`s an exception regarding lg G, which confers immunity to the newborn through the placental transfer of these antibodies, transfer that is realized through endocytosis mediated by receptors or through solutions of continuity of the membranes.
- Lipids – The lipid concentration at the fetus is smaller. The one that is important is arachidonic acid – an important element for fetal development.
- Monovalent Cations – The sodium pump is found in the trophoblast, the transport of the sodium being important in regulating the trophoblastic pH.
- Anions – Since the thyroid hormones don`t cross the placenta, providing iodine to the fetus is essential. The transportation is made actively and the fetal concentrations are higher than the maternal ones.
- Calcium – The calcium`s transfer is made through active transport. During the third trimester of pregnancy, the calcium`s concentration at the fetus exceeds maternal concentration.
- Metals – The transfer of iron reaches its peak during the third trimester of pregnancy, receptor-mediated endocytosis (clathrin-mediated endocytosis) being the type of transfer. Zinc is involved in enzymatic activity.
- Substances that Ensures the Maintenance of Pregnancy &Modifies the Fetal Growth – These substances pass through a mechanism of slow diffusion: steroid and protein hormones.
From steroid hormones: estrogen, progesterone and androgens, pass slowly through the placental barrier, and their transplacental diffusion is influenced by their fixation on the carrier proteins.
From protein hormones: ACTH doesn`t cross the placenta, the insulin passes but in low quantities, and for hCG hasn`t been yet described a mechanism for passage.
Endocrine Function of the Placenta
It`s known that the human placenta produces over 30 hormones and has receptors for almost all factors of regulation, being the main major endocrine organ during pregnancy. Syncytiotrophoblast and villous cytotrophoblast are the main places of the hormonal production.
The placenta produces steroid hormones, protein hormones, cytokines and growth factors.
- Steroidogenesis during Pregnancy – During pregnancy, the placenta synthesizes large quantities of progesterone and estrogen, hormones that are secreted in the maternal and fetal blood compartment. They act against the maternal genital tract and metabolic systems, and assure a normal evolution of the pregnancy.
The essential condition for maintaining pregnancy is the functionality of the pregnancy body and the extension of the progesterone`s secretion, especially until the placental steroids are able to support the pregnancy on their own. The steroids that are produced by the placenta derive from precursors provided by the mother or fetus, are metabolized and conjugated. This particular way of biosynthesis of the steroids by the placenta explains the usage of the “fetoplacental unit” or “maternal-placental-fetal unit” terminology.
Progesterone is synthesized from the maternal cholesterol. During the last phase of the pregnancy, the placenta produces 250 – 600mg of progesterone on a daily basis. The production of this hormone depends firstly by the LDL associated cholesterol and an adequate blood flow. Estrogens increase the formation of progesterone from the cholesterol.
Estrogens are secreted, as progesterone, by the pregnancy yellow body during the first weeks of pregnancy, and their role extends until the end of the second month when their synthesis is provided by the fetoplacental unit. – Click here!
Estrogens synthesized by the fetoplacental unit are in most part channeled towards the maternal compartment and partially towards the amniotic liquid.
The secretion in the maternal blood is of 10 – 15mg/day of estradiol and 40 – 50mg/day for estriol. Most estrogens produced by the fetoplacental unit are secreted by the maternal kidney, and this way of elimination requires the transformation of estrogens in metabolites, conjugation that happens at the liver`s level, in the small intestine and kidney, and the renal elimination occurs in different ways for different estrogens.
In the last trimester of pregnancy, the radio-immunological estrogens from the maternal compartment are dosed to assess the functional status of the placenta and fetus. Still, these results are modified by certain circumstances: posture or dieresis`s volume.
The secretion`s control is made through the gonadotropins. Prolactin plays an inhibitory effect against the secretion of estrogen.
- The Protein Hormones – The placenta secretes several proteins in the maternal blood: hormones, proteins with enzymatic activity and proteins with biological functions.
HCG (human chrionic gonadotropin), produced by sincitotrofoblast is secreted into the maternal circulation, and small quantities in the fetal one. The placenta contains a similar quantity of hCG with the one from the serum, which suggests that this hormone isn`t stored in the placenta, but is continually released into circulation. Gonadotrophin`s functions are: it stimulates steroidogenesis and various tissues, sustains the luteal function during the course of fertile cycles stimulating the synthesis of progesterone and estrogen in the gestation body.
The main use in practice is related to the diagnosis of the pregnancy during the first stages of evolution, diagnosis and monitoring subsequent of the molar pregnancy and choriocarcinoma.
Somatotroph chorionic hormone (HCS, human placental lactogen HPL) is synthesized and produced in the syncytiotrophoblast. The placental secretion rate is very high, being a major product in the placenta at term. The serum is proportional to the placenta`s weight, it increases from 5 – 6 weeks, reaching at maximum 36 weeks.
Hormone roles: regulates fetal growth interfering with the metabolism of carbs and fats, owns proliferative effects on mammary gland.
The adjustment of its production is semiautonomous, and its dosage can be achieved through radio-immunological methods, being considered as one of the best markers of placental function and of the fetus`s status indirectly.
Thyroid stimulating hormone is a protein with big molecular weight of which activity increases during pregnancy. It owns antigenic properties due to its structure, thus making its immunological dosage possible. During pregnancy, its levels are higher during the first 2 trimesters, reaching minimal values at term.
Corticotropin chorionic hormone (corticotropin-releasing hormone) has similar properties to ACTH, its structure not being well defined. Its levels increase gradually during pregnancy.
Protective Role of the Placenta
The trophoblast unit represents the interface between the fetoplacental unit and the maternal endometrium.
One of the aspects of the immunological processes is in relation with the presence of cytokines in the fetoplacental unit. Cytokines represent a wide group of polypeptides that include interleukins, TNS alpha and beta interferons, representing chemical messengers of the manifest cellular interactions in the immune response and effectors in the immune processes.
Non Endocrine Metabolic Function of the Placenta
The placental metabolism reaches high levels comparable to those of adult organs, presenting some characteristics of the liver, lung, kidney or of some endocrine organs, but the placental metabolism isn`t totally autonomous.
The placenta ensures the thermoregulation of the fetus during prenatal life. Normally, the temperature of the human fetus is 0.5 ° C higher than the mother, and this gradient is determined by the level of the placental perfusion as well as the direction of the blood in the placenta.
Cloaking from the Mother`s Immune System
The placenta along with the fetus might be “viewed” as a foreign allograft in the mother`s body, and therefore escape from attack by the immune system of the mother. For this particular purpose, the mother`s placenta uses a few mechanisms:
- It starts secreting phosphocholine molecules that contain Neurokinin B, the very same mechanism that is used by parasitic nematodes to avoid being detected by their host`s immune system.
- There`s presence of very small fetal lymphocytic suppressor cells which inhibit the mother`s cytotoxic T cells by simply inhibiting the response to interleukin 2.
Still, the placental barrier isn`t the only means to avoid immunity, as the foreign cells of the fetus persist in the mother`s circulation as well on the placental barrier`s other side.
This organ offers a blood reservoir to the fetus as well, delivering blood if hypotension occurs and vice-versa, much compared to a capacitor.
Why Is It Good to Keep the Placenta?
The placenta represents an organ created by your body to offer your future baby nutrients and oxygen while he`s still in the uterus. However, once the placenta has finished its duty tour, it`s that all? For some of the mothers out there, there answer is obviously no. Some of them will want to keep it, cook it and eat it later to potentially avoid some of the side effects that come after birth. Other ones will probably want to plant it next to a tree to commemorate the entire event.
Why Is It Good to Eat your Placenta?
There are women who support the idea of eating the placenta because it raises their quantity of breast milk and level of energy. They also claim it can level off their hormones, decreasing their chances of insomnia or postpartum depression. However, there weren`t made any studies on these claims, so there`s no evidence to support them.
How Do You Eat the Placenta?
- Consume it through a placenta pill – Encapsulation is the latest when it comes to placental cuisine.
- Cook the placenta on your own – Clean it, drain it for all its blood, cut away the umbilical cord along with the membranes and consume it a maximum couple of days.
- Eat it raw – If you are a fan of placentophagia, then you already know that some of the mammals out there eat their placenta raw. It would suppose to amazing for boosting the healing process immediately after labor.
- Make a smoothie from it – A more enjoyable way of having your placenta raw is to turn it into a smoothie.
- Make a pâté – Almost 20 years ago, Chef Hugh Fearnley-Whittingstall cause a lot of fuss on Channel when fried up a placenta with shallots and garlic, then flambéed and puréed it, only to serve it to 20 relatives and friends as pâté.
- Enjoy it along with your most favorite dishes – You can have it with lasagna by replacing a layer of cheese with a layer of placenta. Or sautée along with spices in a pizza topping.