The traditional Chinese philosophy believes that the universe is basically made of five "elements" viz. wood, fire, earth metal, and water. A man is also a part of nature and hence he is also thought to be comprised of' the five "elements" of the universe.
In nature nothing exists as a single form and separated from the other, indeed there is always some influence of one over the other in such a way that it becomes predominant. In Yin and Yang principle, Yin or Yang never exists separately but there is always some Yin component in Yang and Yang component in Yin. Similarly the five elements cannot be separated from one another in a single subject but the nature of the subject depends on the predominance of the particular element.
The traditional Chinese medicine classified all the internal organs of the body into two groups-"Yang" (Hollow) organs and "Yin" (Solid) organs and accordingly, a particular "Yin" organ and a particular "Yang" organ unite to fall in the regulation of universal law (couple organ).
In other words, a particular Yin and Yang organ are related to a particular element of the universe. The five elements interact with each other to form a constructive or generative (Sheng) cycle or interact in a destructive way to form a destructive (Ko) cycle.
The "Qi" energy circulates among the different elements of the universe to stabilize them and similarly it circulates in human body to make a balanced state (healthy). Any exogenous factor (hot, cold, humidity, virus, bacteria etc.) or endogenous factor (sorrow, fear, anger, shock etc.) may block the flow of vital energy and subsequently the body is diseased.