During Week 2, what key developmental event occurs?

During Week 2, what key developmental event occurs?

• A. The embryo begins to draw on maternal circulation.
• B. The heart beats.
• C. Blood cells circulate.
• D. Placenta forms.

Answer: (A)

Week 2 focuses on establishing access to maternal blood. After implantation, the trophoblast forms lacunae that fill with maternal blood, creating a primitive network through which nutrients and oxygen can diffuse to the developing embryo. This is the start of the embryo drawing on maternal circulation, which supports growth before a fully formed placenta is established. The heart beating begins later (around week 4), and blood cells start circulating a bit later as hematopoietic tissues develop. The placenta itself becomes more clearly defined in the following weeks, but the essential early step is connecting to the maternal circulation for nourishment.

Week 2 focuses on establishing access to maternal blood. After implantation, the trophoblast forms lacunae that fill with maternal blood, creating a primitive network through which nutrients and oxygen can diffuse to the developing embryo. This is the start of the embryo drawing on maternal circulation, which supports growth before a fully formed placenta is established. The heart beating begins later (around week 4), and blood cells start circulating a bit later as hematopoietic tissues develop. The placenta itself becomes more clearly defined in the following weeks, but the essential early step is connecting to the maternal circulation for nourishment.