The Five Elements:

Fire, Earth, Metal, Water, and Wood are the five elements by which nature is further categorized within TCM.  The internal organs, the sense organs, emotions, seasons, colours, shapes, food, climates, and directions are all assigned an element.  These relationships help us to make sense of the natural world and to again strive for balance as with Yin and Yang.  For example, the Wood element governs the Liver, the eyes, anger, Springtime, green, and east.  The star shaped diagram below shows the interelationship between the five elements, which allows us to rebalance them. 

Another example is the Water element governs the Kidney which includes the ears, head hair, reproductive function, the spine, bone marrow, and brain function, the associated colour is black, the season is winter, and the direction is North.  Early signs of the Kidney system not functioning optimally could be dark circles under the eyes, a generally dark complexion, hair loss, hearing loss, low libido, sore lower back, achy knees, or poor memory.