Testbook qns Flashcards
The sclerotome arises from cells that were located in the: A. Notochord B. Paraxial mesoderm C. Intermediate mesoderm D. Lateral plate mesoderm E. None of the above
Ans: B
2. The cardiogenic plate arises from: A. Embryonic endoderm B. Somatic mesoderm C. Splanchnic mesoderm D. Intermediate mesoderm E. Neural crest
Ans: C
An inductive stimulus from which structure stimulates the transformation of the epithelial sclerotome into secondary mesenchyme? A. Neural crest B. Somite C. Ectodermal placodes D. Embryonic endoderm E. Notochord
Ans: E
Which of these structures in the embryo is unsegmented? A. Somitomeres B. Neuromeres C. Notochord D. Somites
Ans: C
The intermediate mesoderm is the precursor of the: A. Urogenital system B. Heart C. Somites D. Body wall E. Vertebral bodies
Ans: A
What forces are involved in the folding of the neural
plate to form the neural tube?
A change in cell shape at the median hinge point and
pressures of the lateral ectoderm acting to push up the
lateral walls of the neural plate.
What role do neuromeres play in the formation of
the central nervous system?
Neuromeres provide the fundamental organization of parts
of the brain in which they are present. Certain homeobox
genes are expressed in a definite sequence along the
neuromeres.
From what structures do the cells that form skeletal
muscles arise?
The somites. Axial muscles form from cells derived from
the medial halves of the somites, and limb muscles arise
from cellular precursors located in the lateral halves of the
somites.
Where do the first blood cells of the embryo form?
In blood islands that arise from mesoderm of the wall of
the yolk sac.
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 α-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
Ans: D. α-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
α-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
Ans: A
Which condition is related to paternal imprinting? A. Accessory placental lobes B. Placenta previa C. Oligohydramnios D. Single umbilical artery E. Hydatidiform mole
Ans: E
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
Ans: B
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
Ans: D
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
Ans: E
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
Ans C
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
A woman in her early 40s who has chronic alcoholism, who smokes heavily, and who also occasionally uses cocaine gives birth to an infant with severe anencephaly. She had previously given birth to a child who had a less severe form of spina bifida. Another child, although small in stature, seemed normal, but had a behavioral problem in school.
What is a likely basis for such a history?
Although this woman’s history suggests many risk factors, In one of her children’s problems could be definitely attributed to any specific cause. Nevertheless, there is a good likelihood that the spina bifida in the first child and the anencephaly of the third child could be related to overall poor nutrition and
a specific deficiency in folic acid because poor nutrition is
common in persons with alcoholism. The small stature of the middle child could possibly result from the mother’s heavy smoking. On the one hand, the behavior problem of the middle child could be a consequence of the mother’s cocaine
use, smoking, or alcohol consumption. On the other hand, there could be no relation between any of the mother’s risk factors and a prenatal influence on the child’s later behavior. An important point is that despite many well-known risk
factors, it is very difficult, if not impossible, to assign a given congenital anomaly to a specific cause. Realistically, one can only speak in terms of probabilities.
Phocomelia is most likely to be seen after maternal
exposure to which teratogenic agent during the first trimester of pregnancy?
A. Alcohol
B. Aminopterin
C. Androgens
D. Ionizing radiation
E. Thalidomide
E
Which of these anomalies can be attributed to a disturbance in tissue resorption? A. Pelvic kidney B. Cleft lip C. Anal atresia D. Renal agenesis E. Amputated digit in utero
C
Which of the following is responsible for the largest percentage of congenital malformations? A. Maternal infections B. Chemical teratogens C. Genetically based conditions D. Ionizing radiations E. Unknown factors
E
