Each of the 12 Primary Meridians has a Yuan point (also called Source Points). They are located near the wrist or ankle joints. Through this points the Vital Energy (Yuan Qi) of the organs passes and accumulates. 
The Lingshu states, “The twelve Yuan (source) points are indicated in disorders of the internal organs. Infact, the Yuan (source) points are of great significance in treating diseases of the internal organs. 
Stimulating the Yuan (source) points stimulates the vital energy of the regular meridians, regulates the functional activities of the internal organs, reinforces antipathogenic factors and eliminates pathogenic factors.