The tissues and organs of the human body may pertain either to Yin and yang according to their relative locations and functions. Viewing the body as a whole, the trunk surface and the four extremities, being on the exterior, pertain to Yang, while the Zang-Fu organs are inside the body and are relatively speaking Yin.
Viewing the body surface and the four extremities along, the back pertains to Yang, while the chest and abdomen pertain to Yin.
The lateral aspect of the four extremities pertains to Yang and the medial aspect to Yin.
The channels running along the lateral aspect of an extremity pertain to Yang and the medial aspect to Yin.
When speaking of the Interior –Exterior (Zang-Fu) organs alone, the Exterior (Fu) organs with their main function of transmitting and digesting food pertain to Yang, while the Interior (Zang) organs with their main function of storing vital essence and vital energy pertain to Yin. Each of the Zang-Fu organs itself can again be divided into Yin or Yang. Eg the Yin and Yang of the Kidney, the Ying and Yang of the Stomach etc.
In short, however complex the tissues and structures of the human body, and their functional activity, they can be generalized and explained by the relation of Yin and Yang.
The interdepending relation of Yin and Yang means that each of the two aspects is the condition for the others existence and neither of them can exist in isolation. For instance, without daytime there would be no night, without excitation there would be no inhibition. Hence, it can be seen that Yin and Yang are at once in opposition and in interdependence; they rely on each other for existence, coexisting in a single entity. The movement and change of a thing are due not only to the opposition and conflict between Yin and Yang but also to their relationship of interdependence and mutual support.
Hence in the Neijing- "Yin is installed in the interior as the material foundation of Yang, while Yang remains on the exterior as the manifestation of the function of Yin".
An imbalance of Yin and Yang occurs in disease. This may occur by a deficiency of Yin (an empty condition) or by an excess of Yin (a full condition), and similarly for Yang.
In an excess of Yin, there is too much cooling occurring from low activity and the result is cold symptoms. If there is an excess of Yang there is too much heating and activity, so hot signs will be evident. When there is an empty condition the patient needs to be tonified (energy increased). In a full conditions the patient needs to be sedated (energy drained). It can be seen that in all treatments the method is to return the Yin Yang and Empty Full balance to normal.
For instance, an acute high fever at the beginning of a Flu is a Full Yang condition, and the treatment is aimed at draining the heat. In the case of a chronic afternoon fever and restlessness, this is still a preponderance of Yang, however is an Empty condition because Yin has been exhausted, and is usually called an Empty Yin condition.
5 Elements
Nourishing cycle (Sheng)
Nourishing implies promoting growth. The order of nourishing is that Wood promotes Fire, Fire nourishes Earth, Earth nourishes Metal, Metal nourished water, and Water in turn nourishes Wood.
When considering one element, it is considered to the “mother” of the next one, and the “son” of the previous one. Hence the nourishing cycle- each nourishes the next.
Using this cycle, if one element is empty, the previous one can be stimulated to nourish the empty one.
Disharmonies of this cycle are empty conditions. For example if the Fire element is empty, Wood element can be stimulated to nourish the Fire. The Fire element corresponds to Heart and Wood to the Liver. So for Heart problems such as restlessness and insomnia the Liver may be treated.
Controlling cycle (Ke)
This is a restraining cycle. In the interacting relation of the five elements, the order is that wood acts on Earth, Earth acts on Water, Water acts on Fire, Fire acts on Metal, and Metal in turn acts on Wood.
Disharmonies of this cycle are full conditions and take the form of