Comprehensive Test Flashcards
The second meiotic division is characterized by which of the following events? (A) Crossing over (B) Cell division (C) Alignment (D) Centromere splitting (E) Synapsis
D. The second meiotic division (meiosis II) is characterized by centromere splitting. Meiosis
is a specialized process of cell division that occurs only in the production of gametes. The process consists of two divisions (meiosis I and meiosis II) that result in the formation of four gametes, each containing half the number of chromosomes (23 chromosomes) and half the amount of DNA (1N) found in normal somatic cells
A 40-year-old woman becomes pregnant. For approximately how long was the primary oocyte that formed the ovum arrested in prophase of meiosis I? (A) 48 hours (B) 1 week (C) 1 month (D) 12 years (E) 40 years
E. The primary oocyte that matured to become the fertilized ovum in this woman remained dormant in prophase of meiosis I for 40 years. Proliferation of oogonia and their differentiation to primary oocytes are completed before birth. All primary oocytes are formed by the fifth month of fetal life and remain arrested in prophase of meiosis I at least until puberty; then from 5 to 15 primary oocytes begin maturation with each ovarian cycle.
Human chorionic gonadotropin (hCG) can first be assayed in the maternal urine (A) at day 8 after fertilization (B) at day 10 after fertilization (C) at day 14 after fertilization (D) during the early fetal period (E) during the late fetal period
B. Human chorionic gonadotropin, which is produced by the syncytiotrophoblast, can be assayed in the maternal urine at day 10 after fertilization and in maternal blood at day 8. Over-the-counter early pregnancy testing kits diagnose pregnancy based on the presence of this hormone.
A young woman was exposed to the rubella virus during pregnancy, which resulted in her baby having a ventriculoseptal cardiac defect. In which period was the mother most likely to have contracted the acute viral infection? (A) Weeks 1-5 before fertilization (B) Weeks 1-5 after fertilization (C) Months 4-5 after fertilization (D) Months 5-6 after fertilization (E) Months 6-7 after fertilization
B. Anomalies related to the congenital rubella syndrome—including cardiac defects, cataracts, and deafness—are seen most commonly in infants who were exposed to the viral infection during weeks 1-5 after fertilization. During this period, the heart, brain, eye, and ear of the embryo are highly sensitive to various teratogens. The risk of congenital anomalies due to rubella infection during the second and third trimesters is low.
The notochord induces the overlying ecto- derm to develop into the (A) skin (B) eye (C) primitive streak (D) primitive node (E) neural plate
E. The notochord induces the overlying ectoderm to differentiate into the neural plate.
A sacrococcygeal teratoma is a tumor that arises from remnants of the (A) neural plate (B) cloaca] membrane (C) posterior neuropore (D) primitive streak (E) notochord
D. The primitive streak normally degenerates and disappears. If remnants persist, the pluripotential cells of the primitive streak can form a sacrococcygeal teratoma.
Unequal division of the truncus arteriosus by the aorticopulmonary septum is most likely to result in (A) patent ductus arteriosus (B) patent foramen ovale (C) coarctation of the aorta (D) pulmonary stenosis (E) interventricular septal defect
D. Abnormal neural crest cell migration may result in the formation of a skewed aorticopulmonary (AP) septum. This usually causes pulmonary stenosis; it sometimes causes pulmonaryatresia if the AP septum is skewed badly.
The ductus arteriosus is derived from which one of the following aortic arches? (A) Right aortic arch 4 (B) Left aortic arch 4 (C) Right aortic arch 5 (D) Right aortic arch 6 (E) Left aortic arch 6
- E. The ductus arteriosus is derived from left aortic arch 6.
Which of the following structures is the fetal component of the placenta? (A) Decidua capsularis (B) Decidua parietalis (C) Decidua hasalis (D) Secondary chorionic villi (E) Tertiary chorionic villi
E. The fetal component of the placenta consists of the tertiary chorionic villi (or villous chorion). The decidua basalis is the maternal component of the placenta.
Which of the following tumors is associated with Rathke's pouch? (A) Cholesteatoma (B) Chordoma (C) Craniopharyngioma (D) Medulloblastoma (E) Pituitary adenoma
C. Craniopharyngiomas, tumors associated with Rathke’s pouch, represent the most common
supratentorial tumors occurring in childhood. These tumors compress the optic chiasm, the
pituitary gland, and the hypothalamus.
The neurohypophysis is derived from the (A) epithalamus (B) hypothalamus (C) metathalamus (D) stomodeum (E) subthalamus
B. The neurohypophysis, the posterior lobe of the pituitary gland, is derived from an outpocketing
of the floor of the hypothalamus. The adenohypophysis, the anterior lobe of the pituitary
gland, develops from an outpouching of the stomodeum, the oral cavity. The metathalamus
consists of the lateral and medial geniculate bodies.
Which of the following adult structures is derived from the ventral mesentery? (A) Greater omentum (B) Falciform ligament (C) Ligamentum venosum (D) Ligamentum arteriosum (E) Median umbilical ligament
B. The falciform ligament and lesser omentum in the adult are derivatives of the ventral
mesentery. The greater omentum forms from the dorsal mesentery. The ligamentum venosum is
a remnant of the ductus venosus, which regresses after birth. The ligamentum arteriosum is a
remnant of the ductus arteriosus, which connects the pulmonary artery and aorta. The median
umbilical ligament is a remnant of the allantois, which becomes a thick fibrous cord in the fetus
called the urachus and extends from the apex of the urinary bladder to the umbilicus. In the
adult, the urachus is called the median umbilical ligament.
Which of the following adult structures is a remnant of the left umbilical vein? (A) Falciform ligament (B) Ligamentum venosum (C) Ligamentum arteriosum (D) Median umbilical ligament (E) Ligamentum teres hepatis
E. The left umbilical vein connects with the ductus venosus to return oxygenated blood from
the placenta to the developing fetus. After birth, the left umbilical vein regresses and its remnant
is known as the ligamentum teres hepatis, or round ligament of the liver.
An obstruction of the pharynx in a neonate caused by a large mass located on the posterior part of the tongue near the foramen cecum is most likely caused by (A) ectopic lymphoid tissue (B) ectopic thymic tissue (C) ectopic thyroid tissue (D) ectopic parathyroid tissue (E) swollen tonsils
C. The thyroid gland forms as an endodermal diverticulum of the foregut. The thyroid diverticulum
migrates caudally but remains connected to the tongue by the thyroglossal duct, which
opens on the tongue at the foramen cecum.
The prostate gland is derived from
(A) the allantois
(B) the paramesonephric duct
(C) the mesonephric duct
(D) endodermal outgrowths from the urethra
(E) endodermal outgrowths from the yolk sac
D. The prostate gland forms from endodermal outgrowths of the prostatic urethra into the
surrounding mesoderm. Initially, about five groups of solid prostatic cords form; by week 11, they
develop lumina and glandular acini. The mesoderm differentiates into the smooth muscle and
connective tissue of the prostate.
