Five Element Theory - Wu Hsing
   
The Wu Hsing model is ingrained in Chinese philosophy, medicine & martial arts.  In the diagram to the right we see the creative cycle.  Water creates wood, wood creates fire, fire creates earth, earth creates metal and metal creates water.  The creative cycle depicts a never ending generative process.  We also see the destructive cycle, it depicts earth destroying water, water destroying fire, fire destroying metal, metal destroying wood and wood destroying earth.  The study of these relationships and correspondences associated with this model can become very deep.  Traditional Chinese Medicine along with Qigong utilize the Wu Hsing theory extensively.      
    The concept of Five Elements is an outcome of yin and yang interactions. The five elements are wood, fire, earth, metal and water. Wood is active, capable of growth and combustion, which is yang. Fire is most active, requiring air for combustion which is most yang. Both wood and fire are above the ground level, which is considered yang. The earth is the ground level, which is neutral. Below the earth are the metal and mineral deposits, which would be regarded as yin. Also, the metal is yin because it is relatively stable compared with the combustible wood. But the most yin of all the five elements is water, which can reach far below the ground level of the earth, lower than the metal. Water is indispensable in the growth of trees so the cycle repeats with wood.
The historical records of the first century B. C. mentioned Zhou Yen who “observed the interactions of yin and yang opposites in nature, the phenomena of the increase and decrease of the yin and the yang, the separation of the Heaven and the Earth, and the movements of the Five Great virtues.” He was credited to have perceived the anatomical relationship in terms of a Five-Element System. This is the only historical evidence available. Therefore, Zhou Yen (350-270 B. C.) is considered as the first to connect yin and yang concept and the Five-Element System. Such a combined yin and yang, Five-Element System constitutes the most important concept in the Cannon of Internal Medicine compiled during the Warring Periods of third century B. C. in China. In fact, such a concept became specialized in the Cannon of Internal Medicine. Each element is associated with a set of organs or functional tissues, together with specific tastes, emotions, seasons, colors and other characteristics. As early as 6th Century B. C. Lao Tzi already mentioned some of these characteristics based on the Five-Element Concept. “The Five colors blind the eye. The five tones deafen the ear. The Five flavors clog the palate. But it was in the Cannon of Internal Medicine that the five elements were first identified with internal organs, emotions and other characteristics.  There is among all these bodily structures and associated characteristics an interdependent, inter-promoting, inter-restraining relation which is in the dynamic state of homeostasis. Its application to Traditional Chinese Medicine is to correlate the natural phenomena with human body and mind. Pathology and therapy should not be a mechanical cause and effect one way street. The effect could influence the cause and there could be mutual influences of the Five-Element dynamics. The interactions of the yin and yang, Five-Element Concept are a guide to medical practice, Qigong practice and prevention of diseases. This system has been developed through thousands of years of clinical experiences in China. 
In summary, your internal organs play a dual role in promoting and maintaining your health: generating and regulating energy for each other. Each organ passes energy to the organ it supports, and, when necessary, controls imbalances in the energy of the organ which it regulates.
The table below shows how the Five Elements relate to others aspects of the mind, body and nature.