There are eight different Extraordinary Vessels and they connect the Six Extraordinary Yang Organs (Uterus, Brain, Marrow, Bones, Blood Vessels and Gallbladder) with the other Organs. For example, the Uterus connects to the Kidneys through the Directing and Penetrating Vessels.
These Extraordinary Vessels are like reservoirs of energy, as opposed to the main Channels which are like rivers. They connect to Channels and balance Yin and Yang flow between them. In effect, Channels can "tap into" the Extraordinary Vessels reserves or store Yin and Yang in them, depending on the needs.
The Directing (Ren Mai 任脉), Governing (Du Mai 督脉) and Penetrating (Chong Mai 冲脉) Vessels are the most important of the eight Vessels because they are the origin of all. Each of the three start directly from the space between both Kidneys because their main task is to supply and circulate Kidney Essence. They can be seen as the three branches of the same Vessel originating from the Kidneys and then taking different pathways. Compared with the other Extraordinary Vessels, these three can be used in clinical practice to influence a patient’s status at a deep fundamental level.
The Directing Vessel is regarded as the ‘Sea of the Yin Channels’ as it has impacts on all the Yin Channels of the body. It starts from the space between the Kidneys, flows through the Uterus down to perineum and then rises up the abdomen along the midline to chest, throat, chin and finally face. It is particularly important for men and women's reproductive system, especially women. It has influence over many female body functions such as puberty, menstruation, fertility, conception, pregnancy, childbirth and menopause.
The Directing Vessel nourishes Yin. It regulates the Uterus by moving Qi into it and into the Lower Burner generally. It support the descending of Lung Qi and the receiving of Qi by the Kidneys. It facilitates Body Fluids transformation, transportation and excretion. It also governs membranes and fat tissues.