The Extrameridian REN begins at the Hui Yin, goes throughout the body and ascends to the lower gum frenulum. Its role is to control all functions of the yin meridians of the body and is called great yin. The REN Channel is in particular in charge of pregnancy and other uterus functions in women.
The REN and DU channels are created by the original qi (yuan qi) and allow for connection and/or separation, which can be seen as dualistic. Thus, if one contemplates these channels as one, after a while he will find the unified chaos before the creation and to get out of this state he will need to refocus on duality. If one contemplates these as separate channels, he will find after a while the energies of yin and yang follow each other and can only coexist with each other and he will have to be recognize them as an unit.
The motion that unifies the two channels is very easy. All you need to do is reach the top of the mouth with the relaxed tip of the tongue, centered on the border between the hard and soft palate.
The proper circulation of energy can be obtained only by healthy people. It ascends the DU and descends the REN channel, which is widely known as „small heavenly orbit”.