Anatomy and Physiology II Practice Test

During which gestational weeks does the embryonic phase of development occur?

1. Week 1 to week 3

2. Week 3 to week 8

3. Week 9 to week 15

4. Week 20 to week 25

The correct answer is: Week 3 to week 8

The embryonic phase of development occurs between week 3 and week 8 of gestation. During this critical period, the foundational structures of the body are formed, including the development of major organs and systems. This phase is distinguished by the formation of the embryonic disc, which undergoes significant cellular differentiation and morphogenesis. From week 3, the process of gastrulation begins, leading to the formation of the three primary germ layers: ectoderm, mesoderm, and endoderm. Each of these layers will give rise to different tissues and organs in the developing fetus. By the end of week 8, all the major organ systems are initiated, completing the embryonic stage and transitioning into the fetal phase of development, which starts at week 9. The other options refer to gestational periods outside the embryonic phase, such as early fetal development or later stages of gestation, when further growth and maturation of the organs take place rather than the initial formation.