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Yin Yang Application in Physiological Functions

Traditional Chinese medicine (TCM) stresses that humans are a part of nature, and are subject to natural law of balance and harmony. Life activities are resulted from interactions of the body components that work in a harmonious and unified manner. Yin yang theory is used as the basis model to understand how the body attains its harmonious balance physiologically.

As already mentioned, the body's physical forms pertain to yin, while the body's activities or functions pertain to yang. Life is sustained when the body's physical forms and its functions are dynamically balanced; the two aspects mutually restrict and depend on one another. As TCM classics state: "yin essence (nutrient materials) is the material basis for the transformation of yang qi (physiological functions), while the actions of yang qi lead to constant production of yin essence. Yin essence and yang qi mutually transform and consume one another." For the internal organs, consumption of fundamental substances (relatively yang process) ensure them to function, while the organ functions promote material metabolism and in turn produce the fundamental substances for the body (relatively yin process).

According to TCM theory, the four directions of qi movement, including upward, downward, outward and inward, are the basic forms of life activities. The different movements of qi work in a coordinated manner; the ascending balances the descending movement, the outward balances the inward movement. Qi balance is important for promoting the physiological functions of different tissues, organs and meridians.

Inside the body, blood and qi can also pertain to yin and yang respectively. Qi creates blood and promotes its circulation, on the other hand, blood carries and nourishes qi; their relationship is just like the mutual dependent relationship of yin and yang. The internal organs are grouped according to their yin and yang characters. The five yin organs (heart, liver, spleen, lungs and kidneys) are solid organs and mainly responsible for the storage of essence and qi (relatively yin function); while the six yang organs (gallbladder, stomach, large intestine, small intestine, bladder and triple burners) are hollow organs and mainly responsible for digestion, transmission and excretion of the body (relatively yang functions). Normal physiological functions are based on interdependent and interactive relationships between the yin and yang organs.

Traditionally, physicians apply the yin yang concept to represent certain organ properties or describe particular functions of the body.

Yin Yang
Descending tendency (downward) Ascending tendency (upward)
Accumulating tendency (inward) Distributing tendency (outward)
Restraining effect Promoting effect
Nourishing and calming actions Warming and propelling actions
Productive processes (yin transform into form) Consumptive processes (yang transform into action)
Heart yin: heart blood and the organ structure Heart yang: pumping blood and "spirit" ruling actions
Liver yin: liver blood and the organ structure Liver yang: regulating blood volume, mental and emotional activities
Spleen yin: spleen fluid and the organ structure Spleen yang: ruling digestion, distributing nutrient essence and controlling blood flow
Lung yin: lung fluid and the organ structure Lung yang: ruling qi, managing respiration, and assisting with the heart to promote blood circulation
Kidney yin: kidney essence and the organ structure Kidney yang: storing essence, producing bone marrow, dominating reproduction and development, and controlling water metabolism