Developmental Toxicology Flashcards
(10 cards)
Diethylstilbestrol (DES):
a. was used to treat morning sickness from the 1940s to the 1970s.
b. was found to affect only female offspring in exposed pregnancies.
c. greatly affects the development of the fetal brain.
d. exposure increases the risk of clear cell adenocarcinoma of the vagina.
e. is now used to treat leprosy patients.
Correct Answer: d.
Explanation: DES is a synthetic estrogen once used in pregnancy, later found to increase the risk of clear cell adenocarcinoma of the vagina in female offspring. This is the hallmark effect associated with DES exposure in utero.
Early (prenatal) exposure to which of the following teratogens is most often characterized by
craniofacial dysmorphism?
a. thalidomide.
b. retinol.
c. ethanol.
d. tobacco smoke.
e. diethylstilbestrol (DES).
Correct Answer: c. ethanol.
Explanation: Ethanol exposure during pregnancy, particularly in early stages, can cause Fetal Alcohol Syndrome, which is characterized by craniofacial abnormalities, growth deficits, and neurodevelopmental disorders.
The nervous system is derived from which of the following germ layers?
a. ectoderm.
b. mesoderm.
c. epidermal placodes.
d. paraxial mesoderm.
e. endoderm.
Correct Answer: a. ectoderm.
Explanation: The ectoderm gives rise to the central and peripheral nervous systems, skin, and related structures. This is a key developmental biology fact.
Toxicant exposure during which of the following periods is likely to have the LEAST toxic
effect on the developing fetus?
a. gastrulation.
b. organogenesis.
c. preimplantation.
d. third trimester.
e. first trimester.
Correct Answer: c. preimplantation.
Explanation: During preimplantation, the embryo follows an “all-or-nothing” response: it either recovers completely or is lost. Organogenesis and later periods are more sensitive to malformations.
Regarding prenatal teratogen exposure, which of the following statements is FALSE?
a. Major effects include growth retardation and malformations.
b. Exposure to teratogens during critical developmental periods will have more severe
effects on the fetus.
c. There is considered to be a toxicant level threshold below which the fetus is capable of
repairing itself.
d. The immune system of the fetus is primitive, so the fetus has little to no ability to fight
off chemicals and repair itself.
e. Embryo lethality becomes more likely as the toxic dose is increased.
Correct Answer: d.
Explanation: The statement is false because the fetal immune system does play a limited role, but it’s not the primary determinant of teratogenic sensitivity. The timing of exposure and cellular differentiation state are more important.
Which of the following stages of the cell cycle are important in monitoring DNA damage
and inhibiting progression of the cell cycle?
a. G1–S, anaphase, M–G1.
b. G1–S, S, G2–M.
c. S, prophase, G1.
d. G2–M, prophase.
e. M–G1, anaphase
Correct Answer: b. G1–S, S, G2–M.
Explanation: These checkpoints help monitor and pause the cell cycle to repair DNA damage before replication or mitosis proceeds. The G1/S and G2/M transitions are especially critical.
Which of the following molecules is NOT important in determining the ultimate outcome of
embryonal DNA damage?
a. p53.
b. Bax.
c. Bcl-2.
d. c-Myc.
e. NF-κB.
Correct Answer: e. NF-κB.
Explanation: While NF-κB plays a role in inflammation and immune responses, it is not a key regulator in the context of DNA damage responses in embryonic cells. Molecules like p53, Bax, and Bcl-2 are more central.
Which of the following is NOT a physiologic response to pregnancy?
a. increased cardiac output.
b. increased blood volume.
c. increased peripheral vascular resistance.
d. decreased plasma proteins.
e. increased extracellular space.
Correct Answer: c. increased peripheral vascular resistance.
Explanation: During pregnancy, vascular resistance decreases to accommodate increased blood volume and maintain uteroplacental perfusion. This helps lower blood pressure despite fluid retention.
All of the following statements are true EXCEPT:
a. Offspring of white mothers have a higher incidence of cleft lip or palate than do black
mothers, after adjusting for paternal race.
b. Cytomegalovirus (CMV) is a common viral cause of birth defects.
c. Folate supplementation during pregnancy decreases the risk of neural tube defects.
d. Cigarette smoke and ethanol are both toxic to the placenta.
e. In humans, there is a negative correlation between stress and low birth weight.
Correct Answer: e.
Explanation: While stress and low birth weight are linked, the statement about a negative correlation is overly broad and less substantiated compared to the other well-established facts.
Which of the following is NOT a mechanism involving the endocrine system by which
chemicals induce developmental toxicity?
a. acting as steroid hormone receptor ligands.
b. disrupting normal function of steroid hormone metabolizing enzymes.
c. disturbing the release of hormones from the hypothalamus.
d. disturbing the release of hormones from the pituitary gland.
e. elimination of natural hormones.
Correct Answer: e. elimination of natural hormones.
Explanation: The elimination of hormones is not a typical mechanism of endocrine disruption. Most endocrine disruptors work by mimicking, blocking, or altering hormone receptor interactions or synthesis/metabolism.
