(1) is produced by the embryonic disk cells (2) is excreted in the maternal urine (3) inhibits
progesterone production (4) maintains the corpus luteum of the maternal ovary
21. The events of the third week of the human embryonic development are as
follows:
(1) the second stage of gastrulation and trilaminar embryo formation (2) development of
axial organs and their initial differentiation (3) formation of the primitive cardiovascular
system (4) further development of chorionic villi
22. The following statements regarding the primitive cardiovascular system
formation are true:
(1) angiogenesis begins in the yolk sac, the connecting stalk, and the chorion (2)
development of embryonic vessels begins later (3) the primitive heart arises from the
mesenchyme and appears like paired endothelial channels (4) the cardiovascular system
is the last system to attain a functional state
23. The following statements regarding the selective exchange through the
placental barrier are true:
(1) antibodies cannot cross the barrier (2) gases, electrolytes, some nutrients, and wastes
freely pass the barrier by simple diffusion (3) red blood cells never pass the barrier (4)
protein hormones do not reach the fetus in significant amounts, steroid hormones freely
pass the barrier
24. The following statements regarding the placental barrier permeability for
dangerous agents are true:
(1) most drugs freely cross the placenta by simple diffusion (2) measles, poliomyelitis, and
rubella viruses may pass through the barrier (3) alcohol and nicotine cross the placental
barrier (4) most of dangerous agents may cause congenital malformations
25. The following statements regarding the placenta metabolism are true:
(1) placenta synthesizes glycogen, cholesterol, and fatty acids (2) syncytiotrophoblast is
the site of placental metabolic activity (3) placenta serves as a source of nutrients and
energy for the embryo (4) placenta cannot synthesize hormones
26. The placenta is the major endocrine gland producing the following hormones:
(1) human chorionic gonadotropin (hCG) (2) human chorionic somatomammotropin (hCS)
(3) relaxin (4) estrogens and progesterone
27. The following statements regarding the umbilical cord are true:
(1) is covered with the amniotic epithelium (2) includes one artery and two veins (3)
contains mucoid connective tissue (4) lacks the allantois and yolk sac remnants
28. The following statements regarding the critical periods of the embryonic
development are true:
(1) developmental disturbances may cause congenital malformations in these periods (2)
implantation is not a critical period (3) the time from the 4th to the 8th weeks is the most
critical period (4) placentation is not a critical period
29. The following statements regarding the allantois are true:
(1) appears on the 16th day as a finger-like projection elongating from the embryo into the
connecting stalk (2) degenerates during the second month, its remnant is found in the
umbilical cord (3) directs blood vessel growth from the embryo towards the chorion (4) its
intraembryonic portion is associated with development of the urinary bladder
