The interrelationships of the Five Elements further explain the body–body-parts correlation and the environment–human correlation as applied to Chinese medicine. The Five Elements theory helps support the Zang manifestation theory, clarify the origins of complicated physiological and pathological conditions, and guide the diagnosis and treatment of diseases. Actually, the Five Elements and Zang manifestation theories reflect various function states in the two different structure levels of the human body system by the systematics view. The human body is a superbly large and open system, with very complicated structural levels.
Wood can be bent and straightened out. Liver (Wood) smooths and discharges to facilitate harmony and averts depression. Fire is red and hot, and tends to flare up, so Heart Yang (Fire) has a warming function. Earth, honest and sincere, produces myriad things. The Spleen (Earth) digests food and distributes essence. Water moistens, flows, and stores, so the Kidney (Water) stores essence and governs Water metabolism, and is the source of Qi and blood generation. Metal is pure, descendent, and astringent. The Lung (Metal) purifies and descends.
The Five Elements theory further explain inner links among viscera functions with the law of promotion and restriction.
(1)Inter-promotion of the five Zang viscera
The Liver (Wood) promotes the Heart (Fire), because the Liver storing blood nourishes the Heart and helps the Heart to control the blood and vessels. The Heart (Fire) warms up the Spleen (Earth), because the Heart governs the blood to nourish the Spleen and regulates the transforming and transporting functions. The Spleen (Earth) supports the Lung (Metal), because the Spleen produces Qi and blood and transports essence up to replenish Lung Qi. The Lung (Metal) nourishes the Kidney (Water), because the Lung purifies and descends Qi to help the Kidney receive Qi, store essence, and control Water metabolism. The Kidney (Water) stores essence, which can transform into blood to nurture the Liver (Wood).
(2)Inter-restriction of the five Zang viscera
The Liver (Wood) restricts the Spleen (Earth), because the Liver (Wood) spreads the unhindered Qi to smooth and relieve the stagnation of the Spleen (Earth). The Spleen (Earth) restricts the Kidney (Water), because the Spleen (Earth) controls the metabolism of Water with transforming and transporting functions to prevent edema by Kidney–Water abnormal overflow. The Kidney (Water) restricts the Heart (Fire), because the Kidney (Water) rises to nourish Heart Yin, which helps the Heart to control hyperactivity. The Heart (Fire) restricts the Lung (Metal), because Heart Yang calms the Lung (Metal) Qi’s dispersing and descending. The Lung (Metal) restricts the Liver (Wood), because the Lung (Metal)’s dispersing and descending prevents hyper-Liver-Yang.
Any of the five Zang viscera is physiologically promoting or being promoted, and restricting or being restricted. This control generation ensures that none of the five Zang viscera is deficient or excessive. For example, Spleen (Earth) Qi is promoted by the Heart (Fire) if it gets deficient, but is restricted by the Liver (Wood) if it gets excessive. This promotion and restriction interconnects the five Zang viscera as one unit, or supports the unity of opposites in the body’s inner environment.
The Classic of Questions points out, as being consistent with the aforementioned principle, “Liver disease may spread to the Spleen, so the strategy to forestall transmission is to tonify the Spleen”.