أسئلة المحاضرات (8 - 9 - 10) امبريولوجي (قبل التعديل)
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Questions and Answers

What does a urachal fistula indicate?

  • Absence of urachal structures
  • Development of abnormal urinary connections
  • Persistence of the distal part of the urachus
  • Persistence of the whole urachus (correct)

    • Which structure is primarily responsible for embryonic nutrition before placental function begins?

  • Allantois
  • Amniotic fluid
  • Umbilical cord
  • Yolk sac (correct)

    • Which of the following best describes the structure of the umbilical cord?

  • Covered with an amniotic sheath formed from extra-embryonic mesoderm (correct)
  • Covered by a thick fibrous layer with no underlying structures
  • Contains only the definitive yolk sac
  • Includes only two umbilical arteries

    • What physiological change occurs in the umbilical cord during the 6th to 10th week of development?

    <p>Physiological hernia occurs</p> Signup and view all the answers

    What is the significance of cells migrating from the gut to the gonads?

    <p>Formation of germ cells</p> Signup and view all the answers

    What does the left umbilical vein develop into after birth?

    <p>Ligamentum teres of liver</p> Signup and view all the answers

    What type of umbilical cord attachment is characterized by being attached to the margin of the placenta?

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

    Which type of true knot in the umbilical cord affects placental circulation?

    <p>True knot</p> Signup and view all the answers

    What structure does the chorion frondosum contribute to?

    <p>Fetal part of the placenta</p> Signup and view all the answers

    Which type of villi is characterized by containing fetal blood vessels?

    <p>Tertiary villi</p> Signup and view all the answers

    What is the fate of the chorion leave?

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

    What can a long umbilical cord lead to during pregnancy?

    <p>Formation of true knots</p> Signup and view all the answers

    Which anatomical structures are involved in the formation of primary villi?

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

    What is the main source of amniotic fluid in the amniotic cavity?

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

    During which week does the amniotic cavity completely surround the embryo?

    <p>4th week</p> Signup and view all the answers

    What characterizes oligohydramnios?

    <p>Fluid less than 0.5 liters</p> Signup and view all the answers

    Which of the following is NOT a function of the amniotic cavity?

    <p>Fuel fetal metabolism</p> Signup and view all the answers

    What is one cause of polyhydramnios?

    <p>Diabetes in the mother</p> Signup and view all the answers

    What percentage of the amniotic fluid is composed of water?

    <p>99%</p> Signup and view all the answers

    What is a potential consequence of prolonged oligohydramnios?

    <p>Fetal adhesion and anomalies</p> Signup and view all the answers

    Which structure forms the roof of the amniotic cavity during its development?

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

    What is the weight of the placenta in relation to the baby?

    <p>1/6 of baby weight</p> Signup and view all the answers

    Which structure forms the fetal part of the placenta?

    <p>Chorion frondosum</p> Signup and view all the answers

    How does the placenta facilitate respiratory function for the fetus?

    <p>Simple diffusion via the placental barrier</p> Signup and view all the answers

    What is a key characteristic of the maternal surface of the placenta?

    <p>Cobblestone appearance</p> Signup and view all the answers

    At what week of pregnancy do changes in the placental barrier structure occur?

    <p>After the 20th week</p> Signup and view all the answers

    Which hormone is secreted by the placenta to maintain the corpus luteum?

    <p>Human chorionic gonadotropin (HCG)</p> Signup and view all the answers

    What condition is known as accessory placenta?

    <p>Placenta succentriata</p> Signup and view all the answers

    Which function of the placenta involves the elimination of waste products from the fetus?

    <p>Excretory function</p> Signup and view all the answers

    What is the function of the allantois in embryonic development?

    <p>Extension from the yolk sac into the umbilical cord</p> Signup and view all the answers

    Which structure becomes incorporated inside the embryo during the 4th week?

    <p>Yolk sac</p> Signup and view all the answers

    What happens to the extra-embryonic part of the allantois?

    <p>It degenerates</p> Signup and view all the answers

    What is a common feature of Meckel’s diverticulum?

    <p>Containing ectopic pancreatic tissue</p> Signup and view all the answers

    Which of the following options describes a vitelline cyst?

    <p>Persistence of the middle part of the vitelline duct</p> Signup and view all the answers

    What can occur if the vitelline duct is obliterated but not degenerated?

    <p>Vitelline band</p> Signup and view all the answers

    What marks the transition from the primary yolk sac to the second yolk sac?

    <p>Communication through the neurenteric canal</p> Signup and view all the answers

    What does the distal part of the urachus become after its development?

    <p>Median umbilical ligament</p> Signup and view all the answers

    What is a characteristic of placenta percreta?

    <p>Chorionic villi penetrate into the surrounding organs</p> Signup and view all the answers

    Which type of twins arises from the fertilization of two separate eggs?

    <p>Dizygotic twins</p> Signup and view all the answers

    What type of twin formation occurs at the bilaminar stage of development?

    <p>Monoamniotic monochorionic</p> Signup and view all the answers

    Which of the following is not a characteristic of monozygotic twins?

    <p>They are completely separate in appearance</p> Signup and view all the answers

    What is the primary cause of conjoined twins?

    <p>Incomplete separation of the embryonic disc</p> Signup and view all the answers

    At which developmental stage do diamniotic dichorionic twins form?

    <p>2 cell stage</p> Signup and view all the answers

    What percentage of twin births are typically dizygotic?

    <p>70%</p> Signup and view all the answers

    Which of the following characteristics applies to dizygotic twins?

    <p>Non-identical genetic makeup</p> Signup and view all the answers

    What is a primary cause of oligohydramnios?

    <p>Renal agenesis</p> Signup and view all the answers

    Which component is primarily responsible for the maintenance of electrolyte balance in the amniotic cavity?

    <p>Fetal kidney</p> Signup and view all the answers

    During which week of development does the amniotic cavity fully encapsulate the embryo?

    <p>Fourth week</p> Signup and view all the answers

    What is the main composition of amniotic fluid?

    <p>99% water</p> Signup and view all the answers

    What is a common fetal anomaly associated with oligohydramnios?

    <p>Fetal adhesion</p> Signup and view all the answers

    What source primarily contributes to the production of amniotic fluid at later stages of fetal development?

    <p>Fetal kidney</p> Signup and view all the answers

    What is the primary role of the yolk sac before the function of the liver begins?

    <p>Nutritional provision to the embryo</p> Signup and view all the answers

    Which structure is formed from the allantois after birth?

    <p>Median umbilical ligament</p> Signup and view all the answers

    What is the fate of the intra-embryonic part of the allantois?

    <p>It forms the median umbilical ligament</p> Signup and view all the answers

    During which week does physiological hernia occur as a normal developmental change?

    <p>6th to 10th week</p> Signup and view all the answers

    Which anomaly is characterized by the persistence of the whole vitelline duct?

    <p>Vitelline fistula</p> Signup and view all the answers

    What is the correct description of the primitive umbilical cord's diameter?

    <p>1 cm</p> Signup and view all the answers

    During which week does the second yolk sac begin to communicate with the amniotic cavity?

    <p>Third week</p> Signup and view all the answers

    What contributes to the formation of Meckel’s diverticulum?

    <p>Persistence of the proximal part of the vitelline duct</p> Signup and view all the answers

    What component is NOT part of the structure of the primitive umbilical cord?

    <p>Amniotic fluid</p> Signup and view all the answers

    Which structure is formed from the medial part of the allantois?

    <p>Median umbilical ligament</p> Signup and view all the answers

    What remains connected to the definitive yolk sac by the vitello-intestinal duct?

    <p>Part of the yolk sac incorporated inside the baby</p> Signup and view all the answers

    In which population is Meckel’s diverticulum more prevalent?

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

    What defines the roof of the primary yolk sac?

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

    What is the primary reason for the occurrence of conjoined twins?

    <p>Incomplete separation of the embryonic disc</p> Signup and view all the answers

    At which stage do diamniotic monochorionic twins develop?

    <p>At the blastocyst stage</p> Signup and view all the answers

    Which type of twins is characterized by being genetically identical?

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

    What configuration characterizes placenta percreta?

    <p>Chorionic villi penetrate myometrium and surrounding organs</p> Signup and view all the answers

    What percentage of twin births is typically attributed to dizygotic formation?

    <p>70%</p> Signup and view all the answers

    Which statement about the appearance of monozygotic twins is true?

    <p>They can share similar fingerprints</p> Signup and view all the answers

    What defines the fetal membranes configuration for diamniotic dichorionic twins?

    <p>2 amnions, 2 chorions, and 2 placentas</p> Signup and view all the answers

    What is a potential site for fusion in conjoined twins?

    <p>Cranial region</p> Signup and view all the answers

    What is the fate of the chorion frondosum during development?

    <p>It forms the fetal part of the placenta.</p> Signup and view all the answers

    Which type of umbilical cord attachment is characterized by the cord being attached away from the placenta?

    <p>Eccentric attachment</p> Signup and view all the answers

    What is a potential consequence of having a true knot in the umbilical cord?

    <p>Loss of placental circulation, leading to fetal death</p> Signup and view all the answers

    What structure is primarily involved in the formation of tertiary villi?

    <p>All listed structures including fetal blood vessels</p> Signup and view all the answers

    Which type of anomaly is characterized by a short umbilical cord?

    <p>Causes fetal demise due to placental separation</p> Signup and view all the answers

    In the context of chorionic development, which type is destined to degenerate?

    <p>Chorion leave</p> Signup and view all the answers

    How do absorbing villi function within the placenta?

    <p>They exchange gases and materials between fetal and maternal blood.</p> Signup and view all the answers

    What results from the degeneration of the definitive yolk sac?

    <p>It results in the loss of nutritional support for the embryo.</p> Signup and view all the answers

    What is the primary protective function of the placenta during pregnancy?

    <p>To protect the fetus against maternal organisms</p> Signup and view all the answers

    Which surface of the placenta exhibits a characteristic cobblestone appearance?

    <p>The maternal surface</p> Signup and view all the answers

    What happens to the structure of the placental barrier after the 20th week of pregnancy?

    <p>It consists only of syncytiotrophoblast and fetal blood vessels</p> Signup and view all the answers

    Which hormone does the placenta primarily secrete to stimulate milk formation during pregnancy?

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

    Which characteristic defines the weight of the placenta in relation to the baby's weight?

    <p>It weighs approximately 1/6 of the baby weight</p> Signup and view all the answers

    What type of placenta anomaly is characterized by an accessory placenta?

    <p>Placenta succentriata</p> Signup and view all the answers

    What is the main function of the placental barrier during fetal development?

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

    Which hormone is primarily responsible for maintaining the corpus luteum in early pregnancy?

    <p>Human chorionic gonadotropin (HCG)</p> Signup and view all the answers

    What is the result of persistence of the entire urachus in embryonic development?

    <p>Urachal fistula.</p> Signup and view all the answers

    During which developmental week does the umbilical cord begin to take shape as a connecting stalk?

    <p>During the 2nd week.</p> Signup and view all the answers

    What are the two primary blood vessels found in a typical umbilical cord?

    <p>Two umbilical arteries and one left umbilical vein.</p> Signup and view all the answers

    What embryonic structure contributes to the formation of the median umbilical ligament after birth?

    <p>Allantois.</p> Signup and view all the answers

    What life-supporting function does the yolk sac provide before the liver takes over?

    <p>Hematopoietic function for RBC formation.</p> Signup and view all the answers

    What anatomical structure do the 2 umbilical arteries become after development?

    <p>They become the medial umbilical ligaments.</p> Signup and view all the answers

    What distinguishes a true knot from a false knot in the umbilical cord?

    <p>A true knot affects placental circulation and can lead to fetal death, while a false knot does not.</p> Signup and view all the answers

    During which stage are tertiary villi formed?

    <p>Tertiary villi are formed when fetal blood vessels develop within them.</p> Signup and view all the answers

    What condition is characterized by the persistent physiological hernia after the 10th week?

    <p>Exomphalos or omphalocele.</p> Signup and view all the answers

    What type of umbilical cord attachment is identified by being attached away from the placenta?

    <p>This is known as a velamentous cord insertion.</p> Signup and view all the answers

    What complications can arise from a short umbilical cord?

    <p>It can lead to premature separation of the umbilical cord.</p> Signup and view all the answers

    What are the primary components that make up primary villi?

    <p>Primary villi are composed of syncytiotrophoblast and cytotrophoblast.</p> Signup and view all the answers

    What are the different shapes of the placenta associated with placenta percreta?

    <p>Zonary, Irregular, Bipartite, and Tripartite.</p> Signup and view all the answers

    What is the genetic difference between dizygotic and monozygotic twins?

    <p>Dizygotic twins are non-identical, whereas monozygotic twins are identical.</p> Signup and view all the answers

    What is one of the key characteristics of conjoined twins?

    <p>Twins may fuse at various body parts like the head or thorax.</p> Signup and view all the answers

    How does the incidence of dizygotic twins compare to that of monozygotic twins?

    <p>Dizygotic twins have a 70% incidence, while monozygotic twins have a 30% incidence.</p> Signup and view all the answers

    How many zygotes are involved in the formation of dizygotic twins?

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

    Describe the process of amniotic fluid circulation in the amniotic cavity.

    <p>Amniotic fluid is produced by amnioblasts and the placenta, is swallowed by the fetus, and excess fluid passes through the urinary system back into the cavity.</p> Signup and view all the answers

    What are two potential causes of oligohydramnios?

    <p>Placental insufficiency and renal agenesis are two potential causes.</p> Signup and view all the answers

    Explain the significance of the amniotic cavity in fetal development.

    <p>The amniotic cavity protects the fetus from trauma and infections, and allows for symmetrical growth and movement.</p> Signup and view all the answers

    What is the maximum volume of amniotic fluid typically present at birth?

    <p>The maximum volume of amniotic fluid at birth is approximately one liter.</p> Signup and view all the answers

    Identify one fetal and one maternal cause of polyhydramnios.

    <p>Esophageal atresia is a fetal cause, while diabetes is a maternal cause of polyhydramnios.</p> Signup and view all the answers

    What characterizes the composition of amniotic fluid?

    <p>Amniotic fluid is composed of 99% water and 1% organics, inorganic salts, and fetal epithelial cells.</p> Signup and view all the answers

    What is one of the main developmental structures that form the floor of the amniotic cavity?

    <p>The floor of the amniotic cavity is formed by epiblasts.</p> Signup and view all the answers

    What effect does the rupture of the amniotic sac have during labor?

    <p>Rupture of the amniotic sac allows the amniotic fluid to wash the vagina, facilitating vaginal birth.</p> Signup and view all the answers

    What anatomical structures form the floor and roof of the primary yolk sac during embryonic development?

    <p>The floor is formed by the hausser membrane and splanchnic extra-embryonic mesoderm, while the roof is formed by hypoblast.</p> Signup and view all the answers

    Describe the fate of the intra-embryonic and extra-embryonic parts of the allantois.

    <p>The extra-embryonic part degenerates, while the intra-embryonic part forms the urachus, which gives rise to the apex of the urinary bladder and the median umbilical ligament.</p> Signup and view all the answers

    What anomalies are associated with the persistence of the vitelline duct?

    <p>Anomalies include vitelline band, vitelline fistula, vitelline sinus, and vitelline cyst.</p> Signup and view all the answers

    What structure is formed from the proximal part of the vitelline duct, and what percentage of people does it affect?

    <p>Meckel’s diverticulum forms from the proximal part of the vitelline duct and occurs in about 2% of people.</p> Signup and view all the answers

    In what manner does the second yolk sac communicate with the amniotic cavity?

    <p>The second yolk sac communicates with the amniotic cavity through the neurenteric canal.</p> Signup and view all the answers

    What key role does the definitive yolk sac play in embryonic development after folding occurs?

    <p>Part of the yolk sac becomes incorporated inside the embryo to form gut, while another part remains outside as the definitive yolk sac.</p> Signup and view all the answers

    What is the anatomical significance of the vitello-intestinal duct?

    <p>The vitello-intestinal duct connects the yolk sac to the embryo and is critical for nutrient transfer during early development.</p> Signup and view all the answers

    What occurs during the 4th week of embryonic development concerning the yolk sac?

    <p>During the 4th week, part of the yolk sac is incorporated into the embryo to form the gut, while the rest remains as the definitive yolk sac linked by the vitello-intestinal duct.</p> Signup and view all the answers

    What is the thickness and weight of the placenta as compared to the baby's weight?

    <p>The placenta is approximately 2 cm thick and weighs about 1/6 of the baby's weight, which is around 0.5 kg.</p> Signup and view all the answers

    Describe the appearance of the maternal surface of the placenta.

    <p>The maternal surface of the placenta has a cobblestone appearance.</p> Signup and view all the answers

    What structures form the placental barrier before the 20th week of pregnancy?

    <p>Before the 20th week, the placental barrier consists of the syncytiotrophoblast, cytotrophoblast, extra-embryonic mesoderm, and fetal blood vessels.</p> Signup and view all the answers

    What is the primary function of the placenta in terms of gas exchange for the fetus?

    <p>The placenta facilitates gas exchange for the fetus through simple diffusion across the placental barrier.</p> Signup and view all the answers

    Which hormones are secreted by the placenta to maintain pregnancy and support fetal development?

    <p>The placenta secretes hormones such as human chorionic gonadotropin (HCG), progesterone, estrogen, lactogen, and relaxin.</p> Signup and view all the answers

    What characterizes placenta previa as an anomaly?

    <p>Placenta previa is characterized by the placenta's abnormal location over the cervix, which can lead to complications during delivery.</p> Signup and view all the answers

    How does the thickness of the placenta change throughout pregnancy?

    <p>The thickness of the placenta can vary but typically remains around 2 cm, particularly in the first and second trimesters.</p> Signup and view all the answers

    Define placenta succenturiata and its significance.

    <p>Placenta succenturiata refers to the presence of an accessory placenta, which can complicate delivery and increase risks of hemorrhage.</p> Signup and view all the answers

    What forms the floor of the primary yolk sac during the second week of development?

    <p>The floor is formed by the Hausser membrane and splanchnic extra-embryonic mesoderm.</p> Signup and view all the answers

    How does the secondary yolk sac communicate with the amniotic cavity?

    <p>It communicates through the neurenteric canal.</p> Signup and view all the answers

    What are the features of Meckel's diverticulum?

    <p>Meckel's diverticulum is present in 2% of people, occurs more commonly in males, is about two inches long, and is located two feet from the ileocecal junction.</p> Signup and view all the answers

    What happens to the extra-embryonic portion of the allantois during development?

    <p>The extra-embryonic part degenerates.</p> Signup and view all the answers

    What structures remain connected by the vitello-intestinal duct?

    <p>The part of the yolk sac incorporated inside the baby and the definitive yolk sac remain connected.</p> Signup and view all the answers

    What anomaly occurs due to the persistence of the distal part of the urachus?

    <p>A urachal sinus is formed.</p> Signup and view all the answers

    What causes the formation of a vitelline fistula?

    <p>A vitelline fistula forms due to the persistence of the entire vitelline duct.</p> Signup and view all the answers

    What are the primary sources of amniotic fluid in the amniotic cavity?

    <p>The primary sources are amnioblasts, the placenta, and the fetal kidneys.</p> Signup and view all the answers

    How does excess amniotic fluid affect the fetus during development?

    <p>Excess amniotic fluid can result in polyhydramnios, causing potential complications such as fetal anomalies and maternal discomfort.</p> Signup and view all the answers

    During which week of development does the amniotic cavity begin to communicate with the yolk sac?

    <p>The amniotic cavity communicates with the yolk sac during the 3rd week of development.</p> Signup and view all the answers

    What are some of the key functions of the amniotic cavity?

    <p>Key functions include preventing infection, protecting against trauma, and allowing free movement to prevent body adhesion.</p> Signup and view all the answers

    What is oligohydramnios and what are its possible causes?

    <p>Oligohydramnios is defined as having less than 0.5 liters of amniotic fluid, potentially caused by placental insufficiency, renal agenesis, or urinary tract obstruction.</p> Signup and view all the answers

    What happens to the amniotic fluid when the fetus swallows it?

    <p>When the fetus swallows amniotic fluid, excess water passes through the urinary system back into the amniotic cavity.</p> Signup and view all the answers

    What is the characteristic composition of amniotic fluid at birth?

    <p>At birth, amniotic fluid is composed of 99% water and 1% organic and inorganic materials.</p> Signup and view all the answers

    What role does the amniotic fluid play during labor?

    <p>During labor, the amniotic fluid helps in dilating the cervix and can wash the vagina upon rupture.</p> Signup and view all the answers

    What is the clinical significance of a persistent urachal diverticulum?

    <p>A persistent urachal diverticulum can lead to complications such as urinary tract infections or the formation of diverticulitis.</p> Signup and view all the answers

    Describe the role of the yolk sac before the liver takes over hematopoiesis.

    <p>The yolk sac is responsible for the formation of red blood cells during early embryonic development until the liver assumes this function.</p> Signup and view all the answers

    What are the main components of the primitive umbilical cord?

    <p>The primitive umbilical cord consists of a connecting stalk, umbilical vessels (two arteries and one vein), allantois, and Wharton’s jelly.</p> Signup and view all the answers

    What anatomical changes occur in the umbilical cord structure during the 4th week of development?

    <p>During the 4th week, the umbilical cord is carried from the caudal end to the ventral surface of the embryo as a result of body folding.</p> Signup and view all the answers

    How does the allantois contribute to fetal development after birth?

    <p>The allantois becomes the median umbilical ligament, which helps maintain the position of the urinary bladder.</p> Signup and view all the answers

    What are the consequences of a true knot in the umbilical cord?

    <p>A true knot can stop placental circulation, potentially causing fetal death.</p> Signup and view all the answers

    Describe the role of anchoring villi in embryonic development.

    <p>Anchoring villi fix the embryonic sac to the endometrium, providing stability for the developing embryo.</p> Signup and view all the answers

    Explain the difference between chorion leave and chorion frondosum.

    <p>Chorion leave is directed towards the decidua capsularis and degenerates, while chorion frondosum forms the fetal part of the placenta at the decidua basalis.</p> Signup and view all the answers

    What happens to the umbilical vein after birth?

    <p>The left umbilical vein becomes the ligamentum teres of the liver post-birth.</p> Signup and view all the answers

    How can the length of the umbilical cord affect pregnancy outcomes?

    <p>A long umbilical cord can lead to true knots formation, while a short cord may cause premature separation.</p> Signup and view all the answers

    What are secondary villi, and what additional structure do they form?

    <p>Secondary villi are formed from syncytiotrophoblast, cytotrophoblast, and somatic extra-embryonic mesoderm.</p> Signup and view all the answers

    What is exomphalos, and when does it occur during development?

    <p>Exomphalos, or omphalocele, is a persistent physiological hernia that occurs after the 10th week of gestation.</p> Signup and view all the answers

    Identify the types of umbilical cord attachment and their characteristics.

    <p>Eccentric attachment is away from the center, marginal is at the placental margin, and velamentous is further away from the placenta.</p> Signup and view all the answers

    What is the characteristic shape of placenta percreta?

    <p>The shape of placenta percreta can be zonary, irregular, bipartite, or tripartite.</p> Signup and view all the answers

    What are the two types of twins based on their formation?

    <p>The two types of twins are dizygotic and monozygotic.</p> Signup and view all the answers

    What is the genetic characteristic of monozygotic twins?

    <p>Monozygotic twins are genetically identical.</p> Signup and view all the answers

    During which developmental stage do diamniotic dichorionic twins form?

    <p>Diamniotic dichorionic twins form at the 2-cell stage.</p> Signup and view all the answers

    What causes conjoined twins to occur?

    <p>Conjoined twins arise due to the incomplete separation of the embryonic disc.</p> Signup and view all the answers

    What is the incidence rate of dizygotic twins compared to monozygotic twins?

    <p>Dizygotic twins have a 70% incidence rate, while monozygotic twins have a 30% incidence rate.</p> Signup and view all the answers

    What are the different types of twin configurations during pregnancy?

    <p>The configurations are diamniotic dichorionic, diamniotic monochorionic, and monoamniotic monochorionic.</p> Signup and view all the answers

    Which type of twins may fuse at the dorsal surface?

    <p>Conjoined twins may fuse at the dorsal surface.</p> Signup and view all the answers

    What are the two main parts of the placenta and which structures form them?

    <p>The fetal part is formed by the chorion frondosum, and the maternal part is formed by the decidua basalis.</p> Signup and view all the answers

    Describe the shape and dimensions of the placenta.

    <p>The placenta has a discoid shape, with a diameter of 20 cm and a thickness of 2 cm.</p> Signup and view all the answers

    What is the placental barrier, and how does its structure change after the 20th week of pregnancy?

    <p>The placental barrier is a membrane separating maternal and fetal blood; after the 20th week, it includes syncytiotrophoblast, extra-embryonic mesoderm, and fetal blood vessels.</p> Signup and view all the answers

    What are the primary functions of the placenta?

    <p>The placenta's main functions are protective, respiratory, excretory, nutritive, and secretory.</p> Signup and view all the answers

    Which hormone secreted by the placenta is responsible for maintaining the corpus luteum during the first four months of pregnancy?

    <p>Human chorionic gonadotropin (HCG) is responsible for maintaining the corpus luteum.</p> Signup and view all the answers

    What is placenta previa, and how does it differ from a succenturiate placenta?

    <p>Placenta previa occurs when the placenta covers the cervix, while a succenturiate placenta is characterized by an accessory placenta.</p> Signup and view all the answers

    How does the placenta facilitate gas exchange for the fetus?

    <p>The placenta facilitates gas exchange through simple diffusion across the placental barrier.</p> Signup and view all the answers

    What is the normal weight of the placenta in relation to fetal weight?

    <p>The placenta weighs approximately 1/6 of the baby's weight, or about 0.5 kg.</p> Signup and view all the answers

    Study Notes

    Fetal Membranes & Twins

    • Fetal membranes surround and protect the developing embryo/fetus, providing a protective environment and allowing for gas exchange, waste removal, and nutrition.
    • The amniotic cavity is filled with amniotic fluid, which cushions the embryo and prevents it from adhering to the membranes.
    • Amniotic fluid is mostly water, with a small percentage of organic and inorganic salts, and fetal epithelium.
    • Amniotic fluid originates in amnioblasts, the placenta, and the fetal kidney.
    • Excess amniotic fluid is absorbed back into the bloodstream, via the fetal kidneys, and waste products are removed by the maternal blood; fetus can also swallow some of the amniotic fluid.

    Amniotic Fluid

    • Definition: Fluid that fills the amniotic cavity, surrounding the embryo.
    • Amount: Approximately one liter at birth.
    • Sources: Amnioblasts, placenta, and fetal kidneys.
    • Structure: Primarily water; also contains inorganic salts, organics, and fetal cells.
    • Circulation: Amniotic fluid is produced and absorbed by the fetus and placenta. Excess fluid is transported via the urinary system back to the amniotic cavity and waste products are returned to maternal blood; fetus can also swallow some of the fluid.

    Oligohydramnios

    • Definition: Amniotic fluid volume less than 0.5 liters.
    • Causes: Placental insufficiency, renal agenesis, urinary tract obstruction.
    • Character: Fetal adhesions, other abnormalities.

    Polyhydramnios

    • Definition: Amniotic fluid volume greater than 2 liters.
    • Causes: Idiopathic (most common), fetal issues (esophageal atresia), or maternal issues (diabetes).
    • Character: Maternal and fetal distress, possible true knots in the umbilical cord.

    Yolk Sac

    • Definition: A cavity related to the ventral surface of the embryo.
    • Development: Formed during the second week, with a floor formed by the Heuser's membrane and a roof formed by the hypoblast. During the third week, it communicates with the amniotic cavity via the neurenteric canal. During the fourth week, some of the yolk sac is incorporated into the developing gut and some becomes the definitive yolk sac. Both are connected by the vitello-intestinal duct.

    Vitelline Duct Anomalies

    • Vitelline band: The vitelline duct is obliterated but not completely degraded.
    • Vitelline fistula: Persistence of the entire vitelline duct.
    • Vitelline sinus: Persistence of the distal portion of the vitelline duct.
    • Vitelline cyst: Persistence of the middle portion of the vitelline duct.
    • Meckel’s diverticulum: Persistence of the proximal vitelline duct (occurs twice as commonly in males). It is approximately two inches long and is positioned a few feet from the ileocecal junction; it can have ectopic gastric or pancreatic tissue.

    Allantois

    • Definition: Extension from the caudal part of the yolk sac into the umbilical cord.
    • Fate: Extra-embryonic part degenerates, while the intra-embryonic part becomes the urachus; the medial part forms the apex of the urinary bladder, and the distal part of the urachus forms the median umbilical ligament.
    • Anomalies: Persistence of the distal part (urachal sinus), middle part (urachal cyst), or the whole urachus (urachal fistula). A urachal diverticulum is the persistence of the proximal part of the urachus.

    Umbilical Cord

    • Development: Forms during the second week as a connecting stalk and becomes positioned ventrally during the fourth week.
    • Structure: Primitive umbilical cord is ~50cm long and ~1cm in diameter and is composed of extra-embryonic mesoderm and the allantois. The umbilical cord contains umbilical vessels (2 arteries & 1 vein). Wharton's jelly surrounds the blood vessels.
    • Changes after birth: Allantois forms umbilical scar; two arteries are the left umbilical arteries; and the left umbilical vein is a ligament running to the liver.
    • Anomalies: Abnormal attachments to the placenta, number of vessels (2 or 3), and knots (true vs. false). Short or long cord and ectopic hernia (omphalocele). Variations in structure are possible.

    Chorion

    • Structure: Syncytiotrophoblast, cytotrophoblast, and somatic extra-embryonic mesoderm.
    • Development: Primary villi develop from the syncytiotrophoblast and cytotrophoblast; Secondary villi develop by the addition of somatic extraembryonic mesoderm; tertiary villi have fetal blood vessels.
    • Types & Fate: Chorion leaves, chorion frondosum (fetal side of the placenta).
    • Function: Anchoring villi fix the embryonic sac to the endometrium; absorbing villi exchange gas and materials between the fetal and maternal blood.

    Placenta

    • Parts: Fetal part (chorion frondosum) and maternal part (Decidua basalis).
    • Structure: Macroscopic structure is discoid, 20cm in diameter, 2cm thick and one-sixth of the fetal weight, with a cobblestone maternal surface and smooth fetal surface with umbilical cord.
    • Microscopic structure: Before 20th week, there are syncytiotrohpblast, cytotrophoblast & extra-embryonic mesoderm & fetal blood vessel. After 20th week, there are syncytiotrohpblast, extra-embryonic mesoderm & fetal blood vessel. Late in pregnancy, there are syncytiotrohpblast and fetal blood vessel.
    • Function: Gas exchange, nutrient transport, waste removal, and hormone secretion.

    Placental anomalies

    • Placenta succentriata: Accessory placenta.
    • Placenta previa: Chorionic villi penetrate the myometrium of the uterine wall to surrounding organs.
    • Placenta percreta: The most severe form of the abnormal placenta previa in which the villi penetrate completely through the uterine wall, or endometrium (this is a more specific term).
    • Number anomalies: Abnormal number or abnormal placement of the placenta. Bipartite, zonary, irregular, or tripartite are terms used to describe variations in placental structure.

    Twins

    • Definition: Delivery of more than one embryo.
    • Causes: Hereditary or medical (administration of exogenous gonadotropins).
    • Types: Dizygotic and monozygotic.
    • Dizygotic: Two oocytes are fertilized by two sperm- the two zygotes are viable and non-identical.
    • Monozygotic: One oocyte is fertilized by one sperm that splits to two zygotes. The zygotes are viable and genetically identical.
    • Conjoined Twins: Occur in monozygotic twins; the twins fuse at various stages of development and can fuse at the head, thorax, ventral surface or dorsal surface- this results in various degrees and locations of fusion.
    • Classification of monozygotic twins: Diamniotic-dichorionic, diamniotic-monochorionic, or monoamniotic-monochorionic, depending on the stage of separation.

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