What is the main organ of the circulatory system?

The main organ of the circulatory system is the heart. It functions as the central pump that circulates blood throughout the body, delivering oxygen and nutrients to tissues while also removing carbon dioxide and waste products. The heart's rhythmic contractions create blood pressure, which is essential for sustaining the flow of blood through a network of arteries, veins, and capillaries.

The lungs, while crucial for gas exchange, are not considered part of the circulatory system; they facilitate the oxygenation of blood but do not pump blood themselves. The brain plays a vital role in regulating many bodily functions, including heart rate and blood pressure, but it is not primarily involved in circulating blood. The liver is involved in processing and detoxifying blood but does not serve as a pump or central organ within the circulatory system. Thus, the heart is unequivocally the key organ responsible for maintaining circulation and is fundamental to the overall function of the circulatory system.