Here's why:
* Early Development: The circulatory system begins to develop very early in the embryo, around three weeks after conception.
* Oxygen and Nutrient Transport: The primary function of the circulatory system is to transport oxygen and nutrients to the developing fetus and remove waste products. This is crucial for the fetus's growth and survival.
* Heart Begins Beating: The heart, a key organ of the circulatory system, starts beating around the 22nd day after conception. This is a crucial milestone marking the beginning of independent blood flow.
While other systems are developing simultaneously, the circulatory system is the first to become functional and essential for the survival of the fetus.
