Final answer:
The disc-like structure where fetal and maternal circulations meet and support the fetus with necessary nutrients and gas exchange is the placenta. It allows for blood from the fetus and the mother to exchange substances without mixing directly, providing a protective environment for the developing fetus.
Step-by-step explanation:
The Placenta: The Disc-Like Structure of Fetal-Maternal Circulation
The disc-like structure where fetal and maternal circulations meet, and where the baby eats, excretes, and breathes is the placenta. As the embryo develops within the mother's uterus, its needs for nutrients and oxygen increase significantly. The placenta is a unique circulatory organ that originates from both the embryo and the uterine wall structures to accommodate the growing embryo's requirements. It is connected to the fetus by the umbilical cord, which includes one umbilical vein and two umbilical arteries. Oxygenated blood is transported from the mother to the fetus, while deoxygenated blood and waste are carried from the fetus to the placenta to be expelled by the mother.
The placenta functions as a selective barrier, permitting the transfer of oxygen, nutrients, and waste products between the mother and fetus without their blood actually mixing. This arrangement protects the fetus from potential immune system reactions from the mother. It is composed of tissues from both the mother and embryo, ensuring efficient exchange of substances and supporting the developing fetus with what it needs to grow and thrive.
Therefore, the correct answer to the student's question is C) Placenta. The amnion encloses the amniotic cavity around the fetus, the chorion helps form the fetal portion of the placenta, and the umbilical cord is the structure that connects the fetus to the placenta, but it is the placenta itself where the crucial exchanges for fetal development occur.