BRS Embryology - Placenta & Fetal Membranes Flashcards
During the later stages of pregnancy, maternal blood is separated from fetal blood by the
(A) syncytiotrophoblast only
(B) cytotrophoblast only
(C) syncytiotrophoblast and cytotrophoblast
(D) syncytiotrophoblast and fetal endothelium
(E) cytotrophoblast and fetal endothelium
D.
During the later stages of pregnancy, the placental membrane becomes very thin and consists of two layers—the syncytiotrophoblast and the fetal endothelium.
The maternal and fetal components of the placenta are
(A) decidua basalis and secondary chorionic villi
(B) decidua capsularis and secondary chorionic villi
(C) decidua parietalis and tertiary chorionic villi
(D) decidua capsularis and villous chorion
(E) decidua basalis and villous chorion
E.
The placenta is a unique organ, in that it is a composite of tissue from two different sources—the mother and fetus. The maternal component is the decidua basalis, and the fetal component is the villous chorion.
The intervillous space of the placenta contains
(A) maternal blood (B) fetal blood (C) maternal and fetal blood (D) amniotic fluid (E) maternal blood and amniotic fluid
A.
The intervillous space contains only maternal blood as the spiral arteries of the endometrium penetrate the outer cytotrophoblast shell.
A young insulin-dependent diabetic woman in her first pregnancy is concerned that her daily injection of insulin will cause a congenital malformation in her baby. What should the physician tell her?
(A) Insulin is highly teratogenic; discontinue treatment
(B) Insulin does not cross the placental membrane
(C) Insulin crosses the placental membrane but is degraded rapidly
(D) Insulin will benefit her baby by increas- ing glucose metabolism
(E) Insulin crosses the placental membrane but is not teratogenic
B.
Insulin, like all protein hormones, does not cross the placental membrane in significant amounts.
What is a normal amount of amniotic fluid at term?
(A) 50 mL (B) 500 mL (C) 1000 mL (D) 1500 mL (E) 2000 mL
C.
The normal amount of amniotic fluid at term is 1000 mL. However, the amount of amniotic fluid at various stages of pregnancy can be indicative of congenital malformations. Oligohydramnios (400 mL in late pregnancy) may be indicative of renal agenesis. Polyhydramnios (2000 mL in late pregnancy) may be indicative of either anencephaly or esophageal atresia.
Which of the following does not pass through the primitive umbilical ring?
(A) Allantois (B) Amnion (C) Yolk sac (D) Connecting stalk (E) Space connecting the intraembryonic and extraembryonic coeloms
B.
The amnion does not pass through the primitive umbilical ring. As craniocaudal folding occurs, the amnion becomes the outer covering of the umbilical cord.
Which of the following best describes the placental components of dizygotic twins?
(A) One placenta, two amniotic sacs, one chorion
(B) One placenta, two amniotic sacs, two chorions
(C) Two placentas, two amniotic sacs, one chorion
(D) Two placentas, two amniotic sacs, two chorions
(E) One placenta, two amniotic sacs, two chorions
D.
Dizygotic twins and 35% of monozygotic twins have two placentas, two amniotic sacs, and two chorions (“222”).
A 26-year-old pregnant woman experiences repeated episodes of bright red vaginal bleeding at week 28, week 32, and week 34 of pregnancy. The bleeding spontaneously subsided each time. Use of ultrasound shows that the placenta is located in the lower right portion of the uterus over the internal os. What is the diagnosis?
(A) Hydatidiform mole (B) Vasa previa (C) Placentaprevia (D) Placental abruption (E) Premature rupture of the amnio- chorionic membrane
C.
A placenta implanted in the lower part of the uterus near the internal os is called placenta previa. The repeated episodes of bright-red vaginal bleeding are caused by the gradual dilation of the uterus in the later stages of pregnancy. As the uterus dilates, spiral arteries and veins supplying the placenta are ruptured. The mother may bleed to death, and the fetus is placed in jeopardy because of the compromised maternal blood flow.
A 19-year-old woman in week 32 of a complication-free pregnancy is rushed to the emergency department because of profuse vaginal bleeding. The bleeding subsides, but afterward no fetal heart sounds can be heard, indicating intrauterine fetal death. The woman goes into labor and delivers a stillborn infant. On examination of the afterbirth, a velamentous placenta is detected. Although not much can be done at this point, what is the diagnosis?
(A) Placenta previa (B) Vasa previa (C) Hydatidiform mole (D) Premature rupture of the amniochorionic membrane (E) Amniotic band syndrome
B.
A velamentous placenta occurs when umbilical blood vessels abnormally travel through the amniochorionic membrane before reaching the placenta proper. If the vessels cross the internal os, a serious condition called vasa previa exists. As the fetus grows dur- ing pregnancy and the amniochorionic membrane stretches, the umbilical vessels may rupture. When that happens, the fetus will bleed to death. The mother is in no danger of bleeding to death in vasa previa because only the umbilical vessels rupture.
A 32-year-old pregnant woman at 30 weeks of gestation comes to her physician because of excess weight gain in a 2-week period. Ultrasonography reveals polyhydram- nios. Which fetal abnormality is most likely responsible for the polyhydramnios?
(A) Bilateral kidney agenesis (B) Umbilical cord knots (C) Velamentous placenta (D) Hypoplastic lungs (E) Esophageal atresia
E.
Polyhydramnios is associated with the inability of the fetus to swallow because of esophageal atresia or anencephaly. Polyhydramnios can also result from absorption defects such as duodenal atresia. The inability of the embryo to swallow the amniotic fluid means that the fluid cannot be absorbed into the fetal blood and removed by the placenta and passed into the maternal blood.
A 25-year-old pregnant woman at 17 weeks of gestation comes to her OB/GYN for a normal examination. During routine blood tests, her serum α-fetoprotein (AFP) concen- tration is found to be markedly decreased for her gestational age. Which abnormality will the physician need to rule out based on these low AFP levels?
(A) Spina bifida (B) Anencephaly (C) Omphalocele (D) Down syndrome (E) Esophageal atresia
D.
Reduced AFP levels are associated with Down syndrome. All of the other defects (neural tube defects such as spina bifida and anencephaly, omphalocele, and esophageal atresias) are associated with elevated AFP levels.
