The eight extraordinary vessels differ from the principal channels in that they do not belong to an organ and do not have their own points; they borrow points from the principal channels. Their function is regulatory, absorbing excess and releasing it when the principal channels are depleted.
Of the eight, two are of particular clinical importance. The Du vessel governs all the yang channels and runs up the back and over the head; the Ren vessel governs all the yin channels and runs up the front. The Chong vessel is called the sea of the twelve channels and is central to gynaecological treatment. The remaining five are used mainly through the eight confluent points.