Flashcards in Testbook qns Deck (43)
The sclerotome arises from cells that were located in
B. Paraxial mesoderm
C. Intermediate mesoderm
D. Lateral plate mesoderm
E. None of the above
2. The cardiogenic plate arises from:
A. Embryonic endoderm
B. Somatic mesoderm
C. Splanchnic mesoderm
D. Intermediate mesoderm
E. Neural crest
An inductive stimulus from which structure
stimulates the transformation of the epithelial
sclerotome into secondary mesenchyme?
A. Neural crest
C. Ectodermal placodes
D. Embryonic endoderm
Which of these structures in the embryo is
The intermediate mesoderm is the precursor of the:
A. Urogenital system
D. Body wall
E. Vertebral bodies
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
From what structures do the cells that form skeletal
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
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
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?
C. Extraembryonic mesoderm
D. Decidual cells
E. None of the above
Which condition is related to paternal imprinting?
A. Accessory placental lobes
B. Placenta previa
D. Single umbilical artery
E. Hydatidiform mole
Blood vessels associated with which structure enter
the fetal component of the placenta?
A. Decidua basalis
D. Yolk sac
E. Decidua parietalis
What type of cells invades the maternal spiral
arteries and reduces the flow of blood from their open
A. Hofbauer cells
C. Fetal erythrocytes
E. Amniotic epithelium
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
A 28-year-old Rh-negative woman’s second son is
born severely jaundiced. Which characteristic most likely
describes her first child?
C. Rh positive
D. Rh negative
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?
D. Ionizing radiation
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
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
Folic acid deficiency is now believed to be a major cause of what class of malformations?
B. Neural tube defects
C. Ambiguous genitalia
Cleft palate is the result of a defect in what developmental mechanism?
A. Failure to fuse
B. Failure to merge
C. Faulty inductive tissue interaction
D. Disturbance in tissue resorption
E. Absence of normal cell death
An increased incidence of what condition is strongly
associated with increasing maternal age?
A. Trisomy 18
B. Trisomy 21
C. Trisomy 13
E. Ambiguous external genitalia
A woman who was in a car accident and sustained
abdominal bruising during the fourth month of pregnancy gave birth to an infant with a cleft palate. She sued the driver of the other car for expenses associated with treatment of the birth defect and claimed that the defect was caused by the accident. You are asked to be a witness for the defense. What is your case?
The conditions that result in cleft palate occur during the
second month of pregnancy. By the fourth month, the
palate is normally completely established. It is almost
certain that this malformation had already been
established by the time of the accident.
A woman who took a new sedative during the second month of pregnancy felt nauseated after ingestion of the drug and stopped taking it after a couple of weeks. She gave birth to an infant who had a septal defect of the heart and sued the manufacturer of the drug. She said that the defect was caused by the drug that made her nauseated. You are asked to be a witness for the manufacturer. What is your case?
Although there may be a connection between the drug
and the birth defect, proving a connection between an
individual case and any drug, especially a new one, is
very difficult. The woman’s genetic background, other
drugs that she may have taken during the same period,
her history of illnesses during early pregnancy, and her
nutritional status should be investigated. Even in the
best of circumstances, the probability that a specific
malformation is caused by a particular factor can only be
estimated in many cases.