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The Application of Yin-Yang Theory to the Field of Traditional Chinese Medicine

The theory of yin and yang is used extensively in traditional Chinese medicine to explain the histological structure, physiological function, and pathological changes of the human body, and to serve as guide for diagnosis of treatment.

The Anatomical and Histological Structure of the Human Body

The Yin-Yang theory asserts that the human body is an organic whole, and there exists an organic connection between all tissues and structures. Yet, at the same time, each of them can be divided into the opposite aspects of yin and yang. Viewing the body as a whole, the portion above the waist pertains to yang and that below belongs to yin; the exterior of the body is associated with yang, while the interior is associated with yin; the back is considered yang and the front, yin; the lateral aspect is yang and the medial, yin.

The zang-fu organs also have yin and yang aspects, the six fu organs are considered yang while the zang organs are yin. Each of the zang-fu organs itself can again be divided into yin or yang; for example, heart yin and heart yang or kidney yin and kidney yang. However complex, all human body structures and tissues can be generalized and explained by the yin-yang relationship. As the Suwen says, "Man has physical shape which is inseparable from yin and yang."

The Physiological Functions of the Human Body

The Yin-Yang theory considers the normal vital activities of the human body to be the result of the relative balance between yin and yang. In traditional Chinese medicine, the physiological functions of the organs and their substances are inseparably related to yin and yang. For example, the activities (yang) of a particular organ are based on that organ's substance (yin) and when either of these aspects is absent, the other cannot function. Thus the result of physiological activities is to constantly promote the transformation of yang into yin essence. If yin and yang cannot maintain relative balance and interaction, they will separate from each other ending the life that depends upon them. As the Suwen says, "When yin keeps balance with yang and both maintain a normal condition of qi, then health will be high-spirited. A separation of yin and yang will lead to the exhaustion of essential qi."

The Pathological Changes of the Human Body

The Yin-Yang theory holds that disease is a result of an imbalance between yin and yang which leads to the hyperactivity or hypoactivity of yin and yang. The occurrence and the development of a disease are also related to zheng qi (body resistance or antipathogenic factors) and xie qi (pathogenic factors). The Yin-Yang theory can be used to generalize the interacting relations between body resistance and antipathogenic factors. Pathogenic factors are divided into yang-natured pathogenic factors and yin-natured pathogenic factors, while zheng qi includes yin essence and yang qi. Yang pathogenic factors may bring about hypoactivity of bodily yang which leads to injury of yin; a heat syndrome results. If the disease is caused by yin pathogenic factors, it may give rise to hypoactivity of yin followed by the injury of yang; a cold syndrome will result. When yang is deficient it fails to restrict yin in the balanced relationship between the two giving rise to xu (deficiency) which is a cold syndrome. The xu heat symptoms complex, however, is caused by a yin deficiency and yang excess. Pathological changes of disease are varied, but can be generally explained in terms of yin-yang imbalance: yin excess causes cold syndromes, yang preponderance leads to heat syndromes, yang deficiency causes cold syndromes, and yin deficiency leads to heat syndromes.

Diagnosis of Diseases

The basic causative factor of disease is an imbalance between yin and yang. Therefore, no matter how intricate and volatile the clinical manifestations are, they can still be summarized into two categories: yin syndromes and yang syndromes. A correct diagnosis depends upon a clear classification of yin and yang syndromes or in the words of the Suwen, "If one is good at diagnosis, they should differentiate the yin from yang after the observation of color (of complexion, tongue, urine, stool, etc.) and feeling the pulse." The four diagnostic methods (inspection, auscultation and olfaction, inquiry, and palpation) also use yin and yang, for example: interior, xu (deficiency), and cold syndromes are considered yin; exterior, shi(excess), and heat syndromes are considered yang; bright color is yang, dim color is yin; a sonorous voice indicates yang, a low voice is yin; feeble and weak respiration is yin, coarse breathing is yang; superficial, rapid, and forceful pulses are yang, slow, deep feeble, and weak pulses are yin.

Applications in Clinical Treatment

Since imbalance and fluctuation of yin and yang are considered the basic causative factors of disease occurrence and development, treatment must readjust yin and yang to their basic state of relative balance. For example, if pathogenic heat, a yang disease causative factor, is overabundant, it consumes the yin fluid and affects the superabundant yang of the body. In this case, the cold methods for heat syndromes (for example, the use of herbs with a "cold" nature to cure "heat" illnesses) is the prescribed treatment. If pathogenic cold is in excess, it will damage the yang qi and exert influence on the body's remaining yin. In this case, the heat method for cold syndromes (for example, the use of herbs with a "hot" nature to cure "cold" illnesses) is sued. Conversely, in cases where yang excess if caused by insufficient yin fluid failing to restrict yang or where yin preponderance is due to yang qi deficiency being unable to control yin, then treatment should reinforce the insufficient yin or yang. The general principle is, "Treat yin for yang diseases, and treat yang for yin disorders."

In medical treatment, the theory of yin and yang is not only used to decide the principles of treatment. This theory is also generally applied to the properties, flavor and action of Chinese herbal medicine as a guide to the clinical administration of herbs. For example, drugs with cold, cool or moist properties are classified as yin and drugs with the opposite properties are classified as yang. Herbs with sour, bitter, or salty flavors are yin, while those with pungent, sweet, or insipid flavors are yang. Drugs with an astringent or descending action are yin and those with an ascending and dispersing action are yang. In clinical treatment, we should determine the principles of treatment based on an analysis of the yin and yang conditions present in terms of their difference yin-yang properties and actions. The goal of clinical treatment is to restore of healthy yin-yang properties and actions. The goal of clinical treatment is to restore a healthy yin-yang balance in the patient.

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