What happens when embryo implants itself in the uterus?

Explanation

### Step-by-Step Solution:

1. **Understanding Implantation**: The process of implantation occurs when the embryo attaches itself to the lining of the uterus after fertilization.

2. **Thickening of the Uterine Wall**: Once the embryo implants itself into the uterus, the uterine wall begins to thicken. This thickening is a crucial change that prepares the uterus for the developing embryo.

3. **Reason for Thickening**: The thickening of the uterine wall happens because the uterus needs to create a supportive environment for the embryo. This support is essential for the embryo's growth and development.

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