Final answer:
The placenta handles the nutrient and waste requirements of the developing fetus during the first several weeks of pregnancy, eventually taking over the function from the decidual cells of the endometrium.
Step-by-step explanation:
The nutrient and waste requirements for the developing fetus are initially managed by the cells of the endometrium, known as decidual cells, which provide nourishment in the very early stages. As the gestation progresses, specifically during the first several weeks, the developing placenta gradually assumes this vital role, supporting the growing embryo with nutrients and managing waste.
Detailed development of the placenta indicates that by prenatal weeks 4-12, the placenta takes over the functions of the decidual cells. The placenta, an organ formed from both maternal and embryonic tissues, serves to exchange nutrients and oxygen from the mother to the fetus and vice versa for waste products through the umbilical cord's vein and arteries.
Therefore, the placenta is the correct answer to the question regarding the handling of nutrient and waste requirements during the initial weeks of fetal development.