"In this context, the respiratory system is like a vital river that goes through two countries; there may be two jurisdictions, but it is still one continous river, whose water flow is oblivious to the ruling government. Just as nature created the river irrespective of political boundaries, the respiratory system is one continuous tract regardless of how academic departments divide it up. If you learn only about parts of the river from the two governments, each with a different perspective, you may not get a comprehensive (or accurate) understanding of the river."