There is a character that predominates according to Yin and Yang for each body structure; however, this predominance is relative. To know if some part of the body is Yin or Yang, we must ask ourselves a question: In relation to what? For example: the back is Yang in relation to the abdomen, but it is Yin in relation to the head. (See: Yin-Yang Opposition Principle)
As a general rule:
- Yang refers to organ functions, the head, what is behind, the exterior, above the waist, Yang organs or viscera, Qi, and the function of defense.
- Yin refers to physical structures, the body, what is in front, the interior, below the waist, Yin organs, blood and body fluids, and nourishment.
Yang Structures
The Yang channels of the body flow along the posterior part, originate or terminate in the head, transport Yang energy, Defensive Qi or Wei Qi, protect the organism from external pathogenic factors. The nature of Yang is, in conclusion, to protect and be on the exterior.
The head is the highest area of the body and, as we mentioned earlier, is the place where Yang channels originate or terminate, whose energy tends to rise. In pathological conditions, heat and fire, wind, or summer-heat (Yang), tend to rise, and the travel route is through Yang channels leading to the head: red eyes or headache are examples of pathogenic Yang energy invading the head.
The skin and muscles are related to the exterior of the body and belong to Yang, protecting the interior. In reference to the umbilicus, what is above it belongs to Yang, and pathogenic factors such as wind can affect it.
The Yang organs have the characteristic of transformation and transportation of energy from food, body fluids, and energy from respiration, and excrete the surplus. Yang is active, and as such they constantly fill and empty, producing Qi as a result of the constant process of transformation and transportation. Constantly, the Yang organs are in contact with the exterior through the mouth, anus, and urethra.
The Yang organs are:
The Yang channels and points on the head can be used to strengthen Yang, increase resistance to external pathogenic factors, or eliminate them if they have penetrated.
The function of each Yang organ is in itself its immaterial part, Yang (Yang within Yang), and within the Yang organs there is a Yin part that is related to the physical structure of that Yang organ itself, as well as blood, fluids, and its essence (Yin within Yang).
Qi is Yang, has the function of warming, protecting, transporting, and elevating. It is related to Wei Qi, which is Yang, circulates through the skin and muscles, protects and warms the body.
The day belongs to Yang, in the 12 hours that belong to the waking moment, Yang energy is responsible for warming the body, producing energy for physical and mental activity. It is this Yang energy that circulates on the exterior of the body protecting the organism. Diseases that begin or worsen during the day are related to Yang fullness or Yang deficiency.
Yin Structures
Yin channels flow along the anterior part of the body. The Qi that comes from nutrition is related to Yin energy, stores life, gives it form, and nourishes it.
The abdomen and chest is the area of the body where these channels originate or terminate.
The internal organs, being in the interior, belong to Yin, and their function is to nourish the body. The nature of Yin is to care for life, be in the interior, and nourish the organism, with a tendency to descend; the pathogenic factors that affect it are dampness and cold.
Below the waist belongs to Yin; pathogenic factors such as dampness more easily affect the legs.
Yin organs have the characteristic of storing the pure essences that result from the transformation and transportation carried out by the Yang organs.
The Yin organs are:
The Yin channels and points on the chest or abdomen (for example the Mu points), in general, can be used to nourish Yin energy.
The physical structure, essence, blood, and fluid of each Yin organ is Yin within Yin, and within each Yin organ there is a Yang part, that is, the function of these organs is Yang within Yin.
Blood is Yin, and as such, nourishes and moistens; it is related to Zhong Qi and Rong Qi, which is Yin, circulates through the internal organs, and nourishes the entire organism.
The night belongs to Yin; the 12 hours related to this time, Yin nourishes the organism, and it is the Yin organs that are responsible for storing the energy produced during the day and the contents that emerge during it, so that matter can transform and grow. Diseases that arise or worsen at night are related to Yin fullness or Yin deficiency.