Abstract
This paper aims at identifying and elaborating the development and functions of the human placenta, an organ that supports growth and development of the fetus. The human placenta is a fetomaternal organ that supports the development of a growing embryo by providing nutrients and gas from the mother to the embryo. Notably, the human placenta facilitates nutrients and gas exchange between the fetus and the mother which helps in maintaining fetomaternal tolerance. The placenta can release metabolic products into fetal and maternal circulations and it also metabolizes various substances. It also protects the fetus against maternal diseases, infections, and certain xenobiotic molecules. Although the placenta is a tough foetal organ, certain factors can have an effect on its health during pregnancy. After delivery, tissues found in the placenta are discarded, and this makes it easy to obtain these tissues for clinical research (Benirschke, 2012, p. 118).
Development of the Placenta and its Functions
Placental Development
As one of the most important and least understood human organ, the placenta starts developing after the blastocyst gets implanted into the maternal endometrium. Notably, all processes involved in the development of the placenta are highly regulated so as to maintain a healthy pregnancy and ensure normal growth of the developing fetal tissue. As an interface link between fetal and maternal tissues, one paramount function of the placenta is to perform vital roles such as; ensuring fetal nutrient supply, and preventing allograft rejection of the fetus (Kay, 2011, p. 611).
The development of the fetal tissues and the placenta goes on for nearly 9 months after fertilization. During the first 4 days of the development in the fallopian tube, the cellular mass shifts and penetrates the uterus where the blastocyst forms at the 5th day. The trophoblast layer and the outer membrane (chorion) are obtained from blastocyst (inner cell mass). There are other extra-embryonic tissues that develop from the blastocyst’s inner mass (Robinson, 2009, p. 221). Within 5 to 8 days of fertilization, the implantation process takes place by aligning the blastocyst to a fine position of the uterus. At the uterine, the implanted blastocyst is supplied with metabolic substances and oxygen from the maternal circulation. Markedly, oxygen and metabolic substances are paramount as they are necessities for embryonic developing growth (In Nicholson, 2013, p. 451).
The invasion process begins after adhesion where the cytotrophoblast cells shift into the decidual layer from trophoblast layer. The lacunar space forms 13 days after fertilization when the vacuoles found in the embryo are confluent to the uterus. After a few weeks, the lacunar space starts developing into the intervillous for blood circulation to take place. The cytotrophoblast cell is the placental progenitor. These cells perform various roles such as supporting the cellular growth of the placenta. Additionally, they are responsible for differentiating and proliferating during gestation. Functions of the specialized epithelium include; waste elimination, transport of gases, nutrient supply, and hormonal synthesis of steroids and peptides that regulate fetal and placental growth (Burton, 2010, p. 73).
The extravillous trophoblasts (EVT) are composed of invasive and proliferative cell layers. The migratory EVT is the third section of EVT that is not proliferative or invasive. Cell population of the trophoblast creates septum, cell islands, chorion leave, and chorionic plate. The proliferative layer grows at the base after the two trophoblasts grow. This gestation period takes approximately 4-5 weeks. The decidua is invaded by the invasive component of EVT to form the interstitial EVT (Blackburn, 2013, p. 119). Also known as the intra-arterial or intramural process is the endovascular invasion that takes place after the cytotrophoblast cells that contained in this layer migrate. The process takes place with the displacement and replacement of vascular endothelial cells. When the anastomoses between the endometrial maternal veins and the dilated spiral arteries take place, maternal blood circulation is allowed within the placental lacunar system in low resistance vessels. The fetus and the placenta are supplied with nutrients and oxygen by maternal blood to allow the removal of metabolic waste from the fetal and placental tissue to the maternal kidney through the umbilical cord for purging (Burton, 2009, p. 74).
After delivery, tissues found in the placenta are discarded, and this makes it easy to obtain these tissues for clinical research. However, in medical research, ethical implications are constantly considered. Due to the low immunogenic properties, these cells represent a good source for allogenic research (In King, 2014, p. 3).
The Role of the Placenta in Pregnancy
Primarily, the placenta keeps the baby alive and well. It ensures that the fetus is fed and toxic waste disposed. It supplies the baby with adequate nutrition acts like a lung for the fetus thereby allowing exchange of gases. It produces hormones that protect the baby and prevents contractions in the uterus by producing hormones. The placenta can release metabolic products into fetal and maternal circulations and it also metabolizes various substances. It also protects the fetus against maternal diseases, infections, and certain xenobiotic molecules (Benirschke, 2012, p. 88). The following are well elaborated points on the role played by the placenta.
The fetus is fed and nourished for nine months by the placenta. The primary role of the placenta is to ensure the exchange of gases, and nutrients in the fetus. Therefore, the placenta greatly influences the health of the baby and the mother by keeping the baby alive and well. The newly formed baby should be supplied with adequate nutrition. The placenta can release metabolic products into fetal and maternal circulations, and it also metabolizes various substances. It also protects the fetus against maternal diseases, infections, and certain xenobiotic molecules. Additionally, it discharges hormones into the fetal and maternal circulations in order to affect metabolism, parturition, pregnancy, and other functions (Kay, 2011, p. 344).
The fetus is supplied with blood from the mother. During this process, blood is transferred to the umbilical cord that is attached to the placenta before reaching the baby. Blood that is transferred from the mother to the fetus contains nutritional substances, oxygen, and glucose. The placenta refines substances before the fetus consumes them. It filters all harmful substances and allows those that are good for the fetus to pass through. Just like the lungs exchange oxygen and carbon dioxide, the placenta allows the transfer of oxygen in the fetus (Power, 2012, p. 43). Once blood with the oxygen is used by the fetus, the blood is transferred to the placenta to pick up more oxygen and get rid of carbon dioxide. The placenta has a critical role of ensuring that products from the baby are discharged into the mother’s circulation and later disposed of through her urine. The baby is also protected by the uterus from any infections as it keeps the baby’s blood and the mother’s blood separate. In this case, it acts as an efficient filter. A long list of the hormones is produced by the placenta. Human placental lactose produced in the largest amount causes the mother to produce more nutrients. For instance, she has more glucose in her circulation to supply the fetus.
Large amounts of female hormones such as progesterone and the estrogen are produced by the placenta. A critical role is played by these hormones in preparing the maternal tissues and the uterus for labor. Before the mother delivers the baby, these hormones also stop any contractions in the uterus. In addition, progesterone and estrogen are responsible for certain exchanges that take place in the mother’s body. Among these hormones are; corticotrophin-releasing hormone and estrogen. They are believed to control the timing of the onset of labor. The placenta metabolizes various substances and releases metabolic products into fetal and maternal circulations.
As the womb stretches and grows, the placenta makes frequent movements to support growth. There are instances when the placenta is low in the womb especially during early pregnancy. In order for it to move to the top, the cervix opens during the third trimester for delivery (Dittmar, 2011, p. 90). During many instances, the placenta either attaches to the side or the top of the uterus. Interestingly, the placenta has no nerve cells. Therefore, it does not directly control the spinal cord or the brain. During pregnancy, the food the mother eats must first be broken down into fine particles of nutrients and proteins across the placenta. Food does not go directly to the baby. During pregnancy, in every minute, 568.26ml of blood that is equivalent to one pint is pumped into the uterus to exchange nutrients with the placenta (Berven, 2010, p. 54).
Precisely, for nine months, the placenta disposes of toxic waste nourishes and feeds the fetus. The placenta contains all ingredients and nutrients needed by the mother. It also supplies the symbiote fetus with blood cells that are well oxygenated (Heffner, 2010). Although the placenta is a tough foetal organ, certain factors can have an effect on its health during pregnancy. Such factors can greatly increase risks of developing problems that are changeable and others are can’t. Some of these problems include; abdominal trauma, high blood pressure, blood-clotting, and maternal age. However, with certain interventions such as ultrasound and Doppler measurement of blood, it is easy to test and evaluate the functioning of the placenta (Iwawaki, 2009, p. 95).
Conclusively, the human placenta facilitates nutrients and gas exchange between the fetus and the mother which helps in maintaining fetomaternal tolerance. It starts developing after the blastocyst gets implanted into the maternal endometrium. The development of the fetal tissues and the placenta goes on for nearly 9 months after fertilization. Notably, all processes involved in the development of the placenta are highly regulated so as to maintain a healthy pregnancy and ensure normal growth of the developing fetal tissue (Hui, 2012, p. 665). Blood that is transferred from the mother to the fetus contains nutritional substances, oxygen, and glucose. The placenta refines substances before the fetus consumes them. It filters all harmful substances and allows those that are good for the fetus to pass through.
Just like the lungs exchange oxygen and carbon dioxide, the placenta allows the transfer of oxygen in the fetus (Burton, 2010, p. 170). The placenta greatly influences the health of the baby and the mother by keeping the baby alive and well. The baby is also protected by the uterus from any infections as it keeps the baby’s blood and the mother’s blood separate (Herlihy, 2014). In this case, it acts as an efficient filter. The newly formed baby must be supplied with adequate nutrition. Before birth, these hormones also stop any contractions in the uterus. In addition, progesterone and estrogen are responsible for certain exchanges that take place in the mother’s body. Among these hormones are; corticotrophin-releasing hormone and estrogen. After delivery, tissues in the placenta are discarded, and this makes it easy to obtain these tissues for clinical research.
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