Development and Function of Placenta

Subject: Midwifery I (Theory)

Overview

The choronion frondosum, one of the fetal components, and the decidua basalis, one of the maternal components, come together to form a placenta, which is an organ. By the start of the third week, the trophoblast produces primary stem villi, which are finger-like buds with an inner core of cytotrophoblast and an outside layer of syncytiotrophoblast. The primary stem villi are known as chorionic villi after the development of the chorion and the appearance of the primitive mesenchyme. By the tenth day, the primary mesoderm invades the primary chorionic villi's central core and changes them into secondary villi. Later, the mesodermal cells in the villi's core develop to become blood vessels, producing the vascular villous system. Tertiary villi are the vascularized villi, and they begin to form by day 21. The decidua basalis and the chorionic frondosum mature into the distinct placenta. It starts in the sixth week and ends in the following one. The placenta increases in thickness and circumference up until the end of the 16th week as a result of the chorionic villi's growth and the intervillous space's corresponding expansion. The thickness does not significantly expand after that, but it does increase circumferentially until term.

Placenta

The maternal component, the decidua basalis, and the fetal component, the choronion frondosum, oppose or fuse to form the placenta, which is an organ.

Development

On the eleventh day, the interstitial implantation is finished, and the blastocyst is surrounded on all sides by lacunar spaces around trabecular cords of syncytial cells. On the thirteenth day, the stem villi emerge from the trabeculae and connect to the basal plate via a chorionic plate. By the start of the third week, the trophoblast produces primary stem villi, which are finger-like buds with an inner core of cytotrophoblast and an outer layer of syncytiotrophoblast. The primary stem villi are known as chorionic villi after the development of the chorion and the appearance of the primitive mesenchyme.

By the tenth day, the primary mesoderm invades the primary chorionic villi's central core and changes them into secondary villi. Later, the mesodermal cells in the villi's core develop to become blood vessels, producing the vascular villous system. Tertiary villi are the vascularized villi, and they begin to form by day 21.

From the stem villi, primary, secondary, and tertiary villi are gradually formed. On the twenty-first day, the arteriocapillary venous system in the mesenchymal core of each villus is finished. In the end, this connects to the intraembryonic vascular network via the body stalk. The decidua basalis and the chorionic frondosum develop into the discrete placenta. It starts in the sixth week and ends in the following one.

The placenta increases in thickness and circumference up until the end of the 16th week as a result of the chorionic villi's growth and the intervillous space's corresponding expansion. The thickness does not significantly expand after that, but it does increase circumferentially until term.

Functions of placenta

  1. Transfer function: The transfer of substances across the placenta involves the following mechanism.
    • Simple diffusion
    • Facilitated diffusion
    • Active transport
    • Pinocytosis
    • Leakage
    • Before delivery, the fetus uses the placenta to absorb oxygen and expel carbon dioxide, a process known as pulmonary exchange. Compared to adult hemoglobin, fetal hemoglobin has a higher capacity to absorb oxygen.
    • Excretory function: Urea, uric acid, and creatinine, among other waste products from the fetus, are expelled to the maternal blood by simple diffusion.
    • Nutritional function: The fetuses receive their nutrients from the mother's blood, and the depletion of the mother's tissue reserves only happens when the diet is insufficient. Thus, a diet high in essential foods is required during pregnancy in order to prevent maternal tissue storage depletion.
  •  Enzymatic functions: Placenta produce enzymes like diamine oxidase, oxytocinase which activate oxytocin and phospholipase A2
  •  Barrier function: The placenta serves as a barrier for the fetus against harmful substances that circulate in the mother's blood. Nearly all medications taken during pregnancy, including insulin, heparin, and others, can pass the placental barrier and harm the developing fetus.
  • Endocrinal function:
    • The cytotrophoblast layer of the chorionic villi produces the human chorionic gonadotrophin hormone. At 7 to 10 weeks of pregnancy, the corpus luteum maintenance reaches its height.
    • Estrogen: During pregnancy, the placenta secretes a significant amount of estrogen when the corpus luteum regresses.
    • Progesterone: Up to the conclusion of labor, the placenta's syncytial layer secretes a significant amount of progesterone.
    • Human placental lactogen: HPL increases for glucose metabolism to support development as HCG levels drop.
  • Placental transfer of heat: The core temperature of a human fetus is 0.5 degrees Celsius higher than that of the mother. Fetal tissue and amniotic fluid have a temperature difference of 0.2 degrees Celsius and 0.1 degrees Celsius, respectively.

REFERENCE

Medline Plus. 05 January 2017 https://medlineplus.gov/ency/article/002398.htm

Medscape. 1994. 2017 http://www.medscape.com/viewarticle/780615_2

England, Marjorie A. Life Before Birth. 2nd ed. England: Mosby-Wolfe, 1996, p.31

Sadler, T.W. Langman's Medical Embryology. 7th edition. Baltimore: Williams & Wilkins 1995, p

 
Things to remember
  • The choronion frondosum, one of the fetal components, and the decidua basalis, one of the maternal components, come together to form a placenta, which is an organ.
  • By the start of the third week, the trophoblast produces primary stem villi, which are finger-like buds with an inner core of cytotrophoblast and an outside layer of syncytiotrophoblast.
  • The primary stem villi are known as chorionic villi after the development of the chorion and the appearance of the primitive mesenchyme.
  • By the tenth day, the primary mesoderm invades the primary chorionic villi's central core and changes them into secondary villi. Later, the mesodermal cells in the villi's core develop to become blood vessels, producing the vascular villous system.
  • Tertiary villi are the vascularized villi, and they begin to form by day 21. The decidua basalis and the chorionic frondosum mature into the distinct placenta.
  • Before delivery, the fetus uses the placenta to absorb oxygen and expel carbon dioxide, a process known as pulmonary exchange.
  • Because the fetuses receive their nutrients from the mother's blood, maternal tissue storage is only depleted when the diet is insufficient.
  • The placenta serves as a barrier for the fetus against harmful substances that circulate in the mother's blood.
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The Placenta: Its Development and Function
Questions and Answers

The blastocyst's interstitial implantation is finished on day eleven when trabecular cords of syncytial cells completely encircle it. The stem villi arise from the trabeculae on the twelfth day and attach to the basal plate via a chorionic plate. The trophoblast has started to produce primary stem villi by the beginning of the third week. These villi resemble finger-like buds and have an inner core of cytotrophoblast and an outer layer of syncytiotrophoblast. The primary stem villi are known as chorionic villi once the chorion has formed and before the rudimentary mesenchyme appears.

By day ten, the primary mesoderm has colonized the primary chorionic villi's central core, converting them into secondary villi. The vascular villous system is created later when the mesodermal cells in the middle of the villi develop into blood vessels. By day 21, tertiary villi, or the vascularized villi, start to form.

The primary, secondary, and tertiary villi are gradually produced by the stem villi. The arteriocapillary venous system in the mesenchymal core of each villus is finished on day twenty-one. Following that, the intraembryonic vascular network is connected to this. The separate placenta develops from the chorionic frondosum and decidua basalis. It begins the sixth week and concludes the following.

Up until the end of the 16th week, the placenta continues to thicken and increase in size as a result of the expansion of the chorionic villi and intervillous space. After that, the thickness doesn't really get any thicker, but the circumference does until the end.

Functions of placenta:

Transfer function: This mechanism is used to transport substances across the placenta.

  • Basic diffusion
  • Diffusion was made easier.
  • Moving actively.
  • Pinocytosis.
  • Leakage.

The following functions are occurring within the transfer functions:

  • Respiratory function: Before delivery, the fetus receives O2 from the placenta and exhales CO2 while the pulmonary exchange occurs. Compared to adult hemoglobin, fetal hemoglobin has a higher capacity to absorb oxygen.
  • Excretory function: Urea, uric acid, and creatinine, among other waste products from the fetus, are excreted into the maternal blood by simple diffusion.
  • Nutritive function: Because the fetuses receive their nutrients from the mother's blood, maternal tissue storage is only depleted when the diet is insufficient. Thus, a diet high in essential foods is required during pregnancy in order to prevent maternal tissue storage depletion.

Enzymatic functions: Enzymes produced by the placenta include phospholipase A2, diamine oxidase, and oxytocinase, which activates oxytocin.

Barrier function: The placenta serves as a barrier for the fetus against harmful substances that circulate in the mother's blood. Nearly all medications taken during pregnancy, including insulin, heparin, and others, can pass the placental barrier and harm the developing fetus.

Endocrinal function:

The cytotrophoblast layer of the chorionic villi produces the human chorionic gonadotrophin hormone. At 7 to 10 weeks of pregnancy, the corpus luteum maintenance reaches its peak.

  • Estrogen: During pregnancy, the placenta secretes a significant amount of estrogen as the corpus luteum regresses.
  • Progesterone: Up until the conclusion of labor, the placenta's syncytial layer secretes a significant amount of progesterone.
  • Human placental lactogen: HPL increases as HCG levels drop, allowing the growth-promoting glucose metabolism.

Placental transfer of heat: Fetal tissue and amniotic fluid are separated in temperature by 0.2 oC, and the uterine wall and amniotic fluid are separated in temperature by 0.1 oC. The core temperature of a human fetus is 0.5 degrees Celsius higher than that of the mother.

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