93 MCQs in Pathology Answers

The Correct option is B


An important characteristic of teratogens is that they work during specific critical periods.

During the pregastrulation period of development (cleavage, blastocyst, early primitive streak) the embryo is refractory to teratogenesis but very sensitive to toxins.

As gastrulation and organogenesis begin, the embryo becomes selectively susceptible to most teratogenic agents.

The critical period is that time when a given organ system or tissue exhibits its greatest sensitivity to a particular teratogen. This period usually corresponds to the time of its most dramatic growth and morphogenesis.

The heart, for example, is most sensitive during the third to fifth weeks, while the critical period for the external genitalia is during weeks eight and nine.

The brain appears to be sensitive to teratogens from the beginning of the third week until the end of pregnancy.

Category: Pathology MCQs