The concept of Qi is essential in Oriental medicine. In English it is often translated as vital energy. This is done to simplify the concept, but actually there is no proper translation. Everything is a manifestation of Qi. It comes in many forms varying from food, breath to sensations. In acupuncture we have for example the specific concepts of Wei Qi (defensive qi), Yuan Qi (source qi) but also for example pathological Qi as a cause of disease.
Unfortunately Qi is often seen as something mysterious or vague by those not familiar with the term. But it can be experienced in specific forms in for example martial arts, qigong and during acupuncture; primarily by the acupuncturist but also by the patient. Although the latter is not necessary for the treatment to be effective. And actually we experience, see, hear and feel it everyday. We just call it differently.
Most people know the Taiji symbol that represents Yin & Yang. But what does it mean? Yin & Yang describe the duality in life. One cannot exist without the other. Examples are dark /light, female / male, cold / hot etc. Because everything is relative to something else there are countless subdivisions. In a medical sense it is also used to describe for example the interior and exterior meridians or the front and back of the body.
Meridians can be seen as channel pathways that run through and over the body. Qi moves through and along these meridians.
12 meridians are coupled to organs. So there are for example the liver, kidney and gallbladder meridians. They influence and carry out certain specific functions. If a meridian is diseased these functions are inhibited and symptoms occur. These can be related to those functions but also can manifest along the pathway of that meridian.
Meridians are our primary treatment focus. With specific needle techniques and materials we aim to tonify, sedate or de-block the meridians. By restoring balance, health is promoted and disease is treated.
The 5 phases, Wuxing (sometimes translated as 5 elements) is a concept that is also much wider ranging than only medicine. Things in every day life, Eastern philosophy and disciplines; all can be based on or devided according to these 5 phases. The phases are Wood, Fire, Earth, Metal and Water.
Between the phases a promoting and controlling cycle exists. This creates a natural self regulating system. The meridians (and coupled organs) belong to a certain phase. The meridian pair Liver-Gallbladder belong to the wood phase for example. What follows out of the interrelational cycles is that the development of disease can be explained and predicted and that possible treatment strategies can be applied according to the dynamics of this system.
Another easy to understand conclusion is that a disturbance in one meridian can cause imbalance in the other. Rarely a pathology stays within one meridian only, especially in chronic conditions.