Functions and Structure of the Placenta
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Questions and Answers

What are the primary components of the placenta?

  • Endometrium and myometrium
  • Chorionic sac and amniotic sac
  • Fetal part and maternal part (correct)
  • Uterine wall and lacunae

    • Which of the following correctly describes the main function of the placenta?

  • It serves as the primary site of nutrient and gas exchange. (correct)
  • It directly nourishes the fetus through maternal blood.
  • It produces hormones essential for fetal development.
  • It provides physical protection for the fetus.

    • In the structure of the placental villi, which features surround the maternal blood pools?

  • Syncytiotrophoblast and cytotrophoblast (correct)
  • Chorionic villi and decidua
  • Maternal arteries and venules
  • Amniotic fluid and fetal membranes

    • What substances are transported from the fetal blood to the maternal blood through the placenta?

    <p>Waste materials and carbon dioxide</p> Signup and view all the answers

    How does the placenta function as a transport system for the fetus?

    <p>By facilitating the exchange of gases and nutrients via the blood supply</p> Signup and view all the answers

    What accurately describes the fetal part of the placenta?

    <p>It arises from the chorionic sac.</p> Signup and view all the answers

    Which layer surrounds the maternal blood pools in the placental villi?

    <p>Syncytiotrophoblast</p> Signup and view all the answers

    In the transport system of the placenta, which of the following substances is primarily transported from the maternal blood to the fetus?

    <p>Nutrients</p> Signup and view all the answers

    Which function of the placenta is crucial for the removal of fetal waste products?

    <p>Carbon dioxide exchange</p> Signup and view all the answers

    What is the role of the umbilical cord in relation to the placenta?

    <p>It facilitates the exchange of substances between the mother and fetus.</p> Signup and view all the answers

    What structure primarily distinguishes the placental membrane in late pregnancy?

    <p>Vasculosyncytial placental membrane</p> Signup and view all the answers

    Which layer is NOT present in the placental membrane during early pregnancy?

    <p>Vasculosyncytial membrane</p> Signup and view all the answers

    Which component of the placental membrane may experience notable thinning during pregnancy?

    <p>Connective tissue</p> Signup and view all the answers

    What is formed by the fusion of the cytotrophoblast and syncytiotrophoblast layers?

    <p>Syncytium</p> Signup and view all the answers

    Which of the following represents one of the primary functions of the placental membrane?

    <p>Separation of maternal and fetal blood</p> Signup and view all the answers

    What primarily composes the vasculosyncytial placental membrane in late pregnancy?

    <p>Syncytiotrophoblast and endothelium of fetal capillaries</p> Signup and view all the answers

    What is the significance of the intervillous space in the placental membrane?

    <p>It is where maternal blood pools for nutrient exchange</p> Signup and view all the answers

    In early pregnancy, how many distinct layers does the placental membrane consist of?

    <p>Four layers</p> Signup and view all the answers

    What happens to the cytotrophoblastic cells in the branch villi after the 20th week of pregnancy?

    <p>They become attenuated and disappear over large areas.</p> Signup and view all the answers

    At full term, which of the following best describes the layers of the placental membrane?

    <p>Three layers comprising syncytiotrophoblast, connective tissue, and endothelium.</p> Signup and view all the answers

    Which structure is primarily responsible for the exchange of oxygen and nutrients between maternal and fetal blood?

    <p>Endothelium of fetal capillaries.</p> Signup and view all the answers

    What primarily characterizes the appearance of syncytiotrophoblast cells in the placental villus?

    <p>They are multinucleated and appear as pink/purple.</p> Signup and view all the answers

    Which of the following changes in the placental structure occurs by the end of pregnancy?

    <p>Reduction in cytotrophoblastic cells across large villous areas.</p> Signup and view all the answers

    Which beneficial substance is primarily involved in the transport of oxygen to the fetus?

    <p>Oxygen (O2)</p> Signup and view all the answers

    Which harmful substance crosses the placental membrane and poses a significant risk to fetal health?

    <p>Cocaine</p> Signup and view all the answers

    What type of immunoglobulin is known to cross the placental membrane to provide passive immunity to the fetus?

    <p>Immunoglobulin G (IgG)</p> Signup and view all the answers

    Which substance is NOT able to cross the placental membrane?

    <p>Immunoglobulin E (IgE)</p> Signup and view all the answers

    Which class of drugs is classified as Category X, indicating an absolute contraindication in pregnancy?

    <p>Aminopterin</p> Signup and view all the answers

    What is a key characteristic of monozygotic twins that distinguishes them from other types of twins?

    <p>They share a common placenta.</p> Signup and view all the answers

    What results from the incomplete division of the embryonic disc in monozygotic twins?

    <p>Formation of conjoint twins.</p> Signup and view all the answers

    How many amniotic sacs do monozygotic twins that result from complete zygote division typically have?

    <p>Two amniotic sacs.</p> Signup and view all the answers

    What type of twins are classified as conjoined twins?

    <p>Monozygotic twins with incomplete embryonic disc division.</p> Signup and view all the answers

    What structural components do monozygotic twins that are not conjoined share?

    <p>One placenta and chorionic cavity.</p> Signup and view all the answers

    What is the primary reason for the difference in size between the donor and recipient twins in Twin Transfusion Syndrome?

    <p>Blood shunting occurs from the donor to the recipient twin.</p> Signup and view all the answers

    What placental abnormality is associated with the donor twin in TTTS?

    <p>Oligohydramnios</p> Signup and view all the answers

    In lethal cases of Twin Transfusion Syndrome, what is a common outcome for the recipient twin?

    <p>Congestive heart failure</p> Signup and view all the answers

    Which of the following best describes the cause of Twin Transfusion Syndrome?

    <p>Anastomosis of placental vessels leading to unequal blood flow.</p> Signup and view all the answers

    What percentage range of monochorionic-diamniotic monozygotic twins are affected by Twin Transfusion Syndrome?

    <p>15% to 30%</p> Signup and view all the answers

    Study Notes

    Functions of the Placenta

    • The placenta is a vital organ, with both fetal and maternal components.
    • The placenta acts as the primary site for nutrient and gas exchange between the mother and the fetus.
    • It works as a transport system, facilitating the movement of substances between the mother and the fetus.
    • Nutrients and oxygen are transported from the mother to the fetus through the placenta.
    • Waste products and carbon dioxide are transported from the fetus to the mother through the placenta.

    Structure of Placental Villi

    • The placental villi have a complex structure, crucial for nutrient exchange.
    • Maternal blood is contained in spaces called lacunas, surrounded by layers known as the cytotrophoblast and syncytiotrophoblast.
    • Fetal blood vessels within the villi access the maternal blood supply for nutrient uptake and waste removal.

    Circulation of Amniotic Fluid

    • The image illustrates the circulation of amniotic fluid, showing its movement between the fetus and its surrounding environment.
    • This fluid is swallowed by the fetus and reintroduced to the amniotic sac.

    Placenta: A Fetomaternal Organ

    • The placenta is a unique organ with both fetal and maternal components, facilitating crucial exchanges between the mother and the developing fetus.

    Placental Functions

    • Nutrient and Gas Exchange: The placenta acts as the primary site for the exchange of nutrients and gases between the mother and fetus, ensuring the fetus's growth and development.
    • Transport System: The placenta, along with the umbilical cord, forms a vital transport system, allowing for the transfer of substances between the mother and fetus.

    Placental Components

    • Fetal Part: Develops from the chorionic sac, the outer layer of the embryo.
    • Maternal Part: Derived from the endometrium, the inner lining of the uterine wall.

    Placental Transport

    • Nutrients and Oxygen: Pass from the mother's blood to the fetal blood
    • Waste Materials and Carbon Dioxide: Pass from the fetal blood to the mother's blood

    Placental Villi: Structural Details

    • Maternal Blood Lacunae: Pools of maternal blood are surrounded by the cytotrophoblast and syncytiotrophoblast layers.
    • Fetal Blood Vessels: Located within the villi, these vessels access the maternal blood supply for nutrient uptake and waste disposal.

    Amniotic Fluid Circulation

    • Amniotic Fluid Exchange: The fluid is circulated and exchanged between the fetus and the surrounding environment.
    • Fluid Swallowing: The fetus swallows amniotic fluid as part of the circulation process.
    • Fluid Return: The fluid is returned to the amniotic sac through various pathways.

    Placental Membrane Composition

    • The placental membrane, also known as the placental barrier, is a complex structure composed of extrafetal tissues.
    • It acts as a barrier between maternal and fetal blood.
    • During early pregnancy, until approximately 20 weeks, the placental membrane consists of four layers:
      • Syncytiotrophoblast (Syncytium)
      • Cytotrophoblast
      • Connective tissue
      • Endothelium of fetal capillaries

    Placental Membrane Changes During Pregnancy

    • The composition of the placental membrane undergoes changes throughout pregnancy.
    • In late pregnancy, the membrane thins significantly in certain areas, forming a vasculosyncytial placental membrane.
    • This thinner structure consists of only two layers:
      • Syncytiotrophoblast (Syncytium)
      • Endothelium of fetal capillaries (vessels)

    Placental Membrane Diagrams

    • Diagram (A): Illustrates the structure of villi during the fourth week of pregnancy, showcasing the layers of the placental membrane, including the decidual layer, spiral artery, intervillous space, blood vessels, cytotrophoblast, and syncytium.
    • Diagram (B): Provides a cross-section of a villus, highlighting the syncytiotrophoblast, cytotrophoblast, connective tissue, and fetal endothelium.
    • Diagram (C): Depicts the layers of the placental membrane in early pregnancy: syncytiotrophoblast, cytotrophoblast, connective tissue, and endothelium of fetal capillaries.
    • Diagram (D): Focuses on the placental barrier, illustrating the exchange of materials between maternal and fetal blood through diffusion. This diagram labels the basal lamina, syncytiotrophoblast, and fetal capillaries.

    Microscopic Changes in Placental Villi

    • After the 20th week of pregnancy, the branch villi undergo significant microscopic changes
    • The cytotrophoblast layer thins out in many villi
    • Over large areas of the villi, cytotrophoblastic cells disappear, leaving only a thin layer of syncytiotrophoblast

    Placental Membrane at Full Term

    • At full term, the placental membrane primarily consists of just three layers:
      • Syncytiotrophoblast (also known as syncytium)
      • Connective tissue of the villus
      • Endothelium of fetal capillaries

    Diagram Description

    • The diagram illustrates a cross-section of a placental villus at full term
    • The villus contains three distinct layers:
      • Syncytiotrophoblast: A layer of multinucleated cells, appearing pink/purple in the diagram
      • Connective tissue of the villus: A layer of supporting tissue surrounding the capillary, appearing in light pink/gray
      • Endothelium of fetal capillaries: The innermost layer, consisting of thin-walled fetal blood vessels, appearing dark purplish-blue
    • The diagram shows oxygen-poor blood entering the capillary, while oxygen-rich blood flows out into the fetal blood vessels
    • It also highlights the syncytial knot
    • The diagram labels key structures, including cytotrophoblast cells, oxygenated and de-oxygenated blood

    Beneficial Substances That Cross the Placental Membrane

    • Oxygen, essential for fetal respiration
    • Carbon dioxide, waste product transported from fetus to mother
    • L-form amino acids, building blocks for fetal growth and development
    • Free fatty acids, provide energy to the fetus
    • Vitamins, crucial for fetal development and function
    • Water, essential for hydration and overall fetal well-being
    • Sodium, chloride, potassium, calcium, and phosphate, involved in electrolyte balance and other vital processes
    • Urea, a waste product from fetal metabolism
    • Uric acid, a waste product of nucleotide breakdown
    • Bilirubin, a waste product from the breakdown of heme
    • Fetal and maternal red blood cells, for oxygen transport
    • Maternal serum proteins, provide nutrients and protection
    • α-fetoprotein, plays a role in fetal development
    • Transferrin-Fe2+ complex, transports iron for fetal growth
    • Low-density lipoprotein, delivers cholesterol for fetal development
    • Prolactin, plays a role in milk production
    • Steroid hormones (unconjugated), essential for fetal development
    • Immunoglobulin G (IgG), provides passive immunity from mother to fetus

    Harmful Substances That Cross the Placental Membrane

    • Viruses, can cause fetal infections and developmental problems
    • Category X drugs (absolute contraindication in pregnancy), pose significant risk to the fetus and should never be used during pregnancy
    • Category D drugs (definite evidence of risk to fetus), have been shown to cause fetal harm and should be used with extreme caution if at all
    • Carbon monoxide, a poisonous gas that can impair fetal oxygen uptake
    • Organic mercury, lead, polychlorinated biphenyls, potassium iodide, heavy metals and environmental toxins that can harm the fetus
    • Cocaine, an addictive stimulant that can cause fetal growth problems and addiction
    • Heroin, an opioid that can cause fetal withdrawal syndrome
    • Toxoplasma gondii, a parasite that can cause fetal brain damage
    • Treponema pallidum, the bacterium that causes syphilis, which can lead to serious fetal complications
    • Listeria monocytogenes, a bacteria that can cause fetal infections
    • Rubella virus vaccine, should not be given during pregnancy, but vaccination prior to pregnancy is recommended
    • Anti-Rh antibodies, can cause fetal anemia if the mother is Rh-negative and the fetus is Rh-positive

    Substances That Do Not Cross the Placental Membrane

    • Maternally derived cholesterol, triglycerides, and phospholipids, large molecules that cannot easily cross the placenta
    • Protein hormones (e.g., insulin), large molecules that cannot easily cross the placenta
    • Drugs (e.g., succinylcholine, curare, heparin, methyldopa), molecules that are too large or have specific properties that prevent them from crossing the placenta
    • Immunoglobulin D, E, M, and A, immunoglobulins that do not cross the placental barrier
    • Bacteria in general, microorganisms that are too large to cross the placenta

    Immunoglobulins (Five Types)

    • Immunoglobulin G (IgG), the only immunoglobulin that can cross the placenta, providing passive immunity
    • Immunoglobulin M (IgM), produced by the fetus after birth
    • Immunoglobulin A (IgA), found in secretions like breast milk
    • Immunoglobulin D (IgD), functions in B cell activation
    • Immunoglobulin E (IgE), involved in allergic reactions

    Monozygotic Twins

    • Monozygotic twins, or identical twins, result from the division of a single fertilized egg (zygote)
    • 65% of monozygotic twins result from the splitting of the zygote at various developmental stages, typically during the early blastocyst stage
    • The inner cell mass divides into two separate cell groups within the same blastocyst cavity
    • The resulting embryos share a common placenta and chorionic cavity but have separate amniotic cavities
    • The fetuses have one placenta, one chorion, and two amniotic sacs

    Conjoint Twins

    • Conjoint twins are a rare form of monozygotic twins
    • The embryonic disc does not fully split or divide
    • These twins share one amnion, one chorion, and one placenta
    • Conjoined twins are connected, resembling two or more pipes or hoses joined to permit a single discharge stream

    Twin Transfusion Syndrome (TTTS)

    • Twin Transfusion Syndrome is a serious complication that can occur in monozygotic twin pregnancies
    • It occurs when there is an imbalance of blood flow between the twins through shared blood vessels in the placenta
    • One twin (the recipient) receives more blood flow than the other twin (the donor)
    • This can lead to a variety of health problems for both twins, including heart failure, anemia, and even death

    Twin Transfusion Syndrome (TTTS)

    • TTTS occurs in 15% to 30% of monochorionic-diamniotic monozygotic twins.
    • TTTS results from abnormal blood flow between twins through arteriovenous anastomoses in the placenta.
    • The donor twin experiences reduced blood flow, leading to anemia, pale skin, and oligohydramnios.
    • The recipient twin receives an excess of blood flow, leading to polycythemia, larger size, and polyhydramnios.
    • The placenta shows abnormalities: the donor twin's portion is pale, and the recipient twin's portion is dark red.
    • TTTS can be fatal, with the donor twin dying from anemia and the recipient twin dying from congestive heart failure.
    • Approximately 65% of monozygotic twins develop from one zygote through division of the inner cell mass.
    • If there is anastomosis of the placental vessels, one twin may receive most of the nutrition from the placenta.

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    Description

    Explore the crucial roles of the placenta, including nutrient exchange and waste removal between mother and fetus. Understand the complex structure of placental villi and the circulation of amniotic fluid. This quiz covers key concepts related to placental biology and physiology.

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