What does the amniotic sac primarily consist of?

The amniotic sac primarily consists of amniotic fluid, which is crucial for the protection and development of the fetus during pregnancy. This fluid surrounds the developing baby and serves several important purposes. It provides a cushioning environment that protects the fetus from physical trauma, allows for movement and growth, and helps maintain a stable temperature. Additionally, amniotic fluid plays a role in the development of the respiratory and gastrointestinal systems, as the fetus inhales and swallows the fluid, which aids in lung maturation and digestion.

In contrast, the other options do not accurately represent the primary composition of the amniotic sac. Blood is involved in nutrient and oxygen delivery but is not a component of the amniotic sac itself. Muscle tissues are not part of the amniotic sac structure, and while placental tissue is vital for fetal development, it is a separate entity from the amniotic sac. Therefore, the presence of amniotic fluid as the primary component highlights its essential role in fetal well-being throughout gestation.