The region of the embryo that first develops a close connection with the uterus is called the -

Options

A. chorion
B. amnion
C. placenta
D. endometrium

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the region of the embryo that first establishes a close connection with the uterus.

2. **Identifying Key Terms**: The key terms in the question are "embryo," "close connection," and "uterus." This indicates that we are looking for a structure associated with the embryo that interacts closely with the uterine environment.

3. **Reviewing Embryonic Structures**: In embryonic development, several extraembryonic membranes form. These include the chorion, amnion, yolk sac, and allantois. Each of these membranes has specific functions and connections.

4. **Focusing on the Chorion**: The chorion is the outermost membrane surrounding the embryo. It plays a crucial role in forming the placenta, which connects the embryo to the mother’s blood supply. The chorionic villi, which are finger-like projections from the chorion, penetrate the uterine lining and establish a close connection with the maternal tissue.

5. **Eliminating Other Options**:
- **Amnion**: This membrane forms the amniotic sac, which provides a protective fluid-filled cavity for the embryo but does not connect directly to the uterus.
- **Placenta**: While it is vital for nutrient and gas exchange, it develops from the chorion and is not the first structure to connect with the uterus.
- **Endometrium**: This is the uterine lining where implantation occurs, but it is not an embryonic structure.

6. **Conclusion**: Based on the above reasoning, the correct answer is the chorion, as it is the region of the embryo that first develops a close connection with the uterus.

**Final Answer**: The region of the embryo that first develops a close connection with the uterus is called the **chorion**.

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