The internal organs of the human body. It is important to understand that the Western scientific concept of the internal organs is entirely different from Zang Fu theory. In Zang Fu theory, there are five main organ systems: Lung, Spleen, Liver, Heart, and Kidney. Each organ system includes a Zang organ and its Fu organ “partner.” In general, Zang organs are solid, and Fu organs are hollow. Each Zang Fu system is responsible for a set of bodily functions that Western science may or may not attribute to those physical organs. For example, the Heart system is responsible for circulating blood (which correlates with Western science), but it is also responsible for memory and thinking (functions that Western science attributes to the brain). Western science and Zang Fu theory are not thought of as antagonistic theories, but more as different ways of viewing the human body. The five organ systems are defined in more detail individually.