Chapter 7: Placenta & Extraembryonic Membranes Flashcards
A 32-year-old woman’s obstetrician notes that her weight gain during late pregnancy is excessive. At least part of her weight gain seems to be the result of a greater than normal volume of amniotic fluid. The patient lives in a remote rural area far from an imaging center. Amniocentesis is performed, and the laboratory report indicates the presence of a high level of alpha-fetoprotein in the amniotic fluid. The obstetrician is concerned that this pregnancy will not result in a normal single birth. What condition does the obstetrician suspect and why?
a. Esophageal atresia
b. Renal agenesis
c. Triplets
d. Anencephaly
e. Placenta previa
d. Anencephaly
alpha-fetoprotein, which is produced principally by the fetal liver, is found in many tissues of the body, but normally, only small amounts are excreted into the amniotic fluid. With open neural tube defects, large quantities of alpha-fetoprotein escape through the opening and enter the amniotic fluid.
In the mature placenta, which fetal tissue directly interfaces with the maternal uterine connective tissue?
a. Cytotrophoblast
b. Syncytiotrophoblast
c. Extraembryonic mesoderm
d. Decidual cells
e. None of the above
a. Cytotrophoblast
Which condition is related to paternal imprinting?
a. Accessory placental lobes
b. Placenta previa
c. Oligohydramnios
d. Single umbilical artery
e. Hydatidiform mole
e. Hydatidiform mole
Blood vessels associated with which structure enter the fetal component of the placenta?
a. Decidua basalis
b. Allantois
c. Amnion
d. Yolk sac
e. Decidua parietalis
b. Allantois
What type of cells invades the maternal spiral arteries and reduces the flow of blood from their open ends?
a. Hofbauer cells
b. Syncytiotrophoblast
c. Fetal erythrocytes
d. Cytotrophoblast
e. Amniotic epithelium
d. Cytotrophoblast
Which condition of the extraembryonic membranes can be found in uteri containing identical twins?
a. Common placenta and amniotic membrane
b. Common placenta and chorion, separate amnions
c. Separate placentas and extraembryonic membranes
d. Common placenta, partially fused chorions
e. All of the above
e. All of the above
A 28-year-old Rh-negative woman’s second son is born severely jaundiced. Which characteristic most likely describes her first child?
a. Male
b. Female
c. Rh positive
d. Rh negative
e. Hydramnios
c. Rh positive
Why is the human placenta designated a hemochorial type of placenta?
Because the placental villi (specializations of the chorion) are directly bathed in maternal blood.
Through what layers of a placental villus must a molecule of oxygen pass to go from the maternal blood into the embryonic circulation?
This depends on the age of the embryo. In an early fetus, the molecule may have to pass through the following layers: syncytiotrophoblast, cytotrophoblast, basal lamina underlying cytotrophoblast, villous mesenchyme, basal lamina of a fetal capillary, and endothelium of the fetal capillary. In a mature placenta, the same molecule may pass from the maternal to the fetal circulation by traversing as few layers as syncytiotrophoblast, a fused basal lamina of trophoblast and capillary endothelium, and the endothelium of a fetal capillary.
What embryonic hormone has served as the basis for many standard pregnancy tests and why?
Human chorionic gonadotropin. This is the first distinctive embryonic hormone to be produced by the trophoblastic tissues. Early pregnancy tests involved injecting small amounts of urine of a woman into female African clawed toads (Xenopus laevis). If the woman was pregnant, the chorionic gonadotropin contained in the urine stimulated the frogs to lay eggs the next day. Contemporary pregnancy tests, which can be done using kits bought over the counter, give almost instantaneous results.
Why must a pregnant woman be very careful of what she eats and drinks?
Many substances that enter a woman’s blood are now known to cross the placental barrier, including alcohol, many drugs (both prescribed and illicit), steroid hormones, and other low-molecular-weight substances. Generally, molecules with molecular weights less than 5000 daltons should be assumed to cross the placental barrier with little difficulty.
