In the course of occurrence, development and final outcome of a discase, harmony of yin and yang will occur under the action of pathogens, resulting in such pathological manifestations as relative excess or deficiency of either yin or yang, mutual impairtment, repellence and depletion of yin and yang.

The Disturbance of qi and blood refers to a morbid state caused by deficiency and dysfunction of qi and blood, and the breakdown of their interdependent relationship. Qi and blood in the body are the material basis for the physiological activities of the zang-fu and meridians. Therefore, their disturbance will inevitably affect the body's functions to cause diseases. Basic Questions states: "The disharmony between qi and blood will result in various diseases". However, qi and blood are the products of the functions of the zang-fu organs. Pathological changes of the z?ng-fu organs may not only lead to qi-blood disturbance, but also affect qi and blood of the whole body. Thus, the pathogenesis of qi-blood disturbance, like that of the rise and decline of vital qi and pathogens and the imbalance of yin and yang, is not only the root cause of pathological changes of the zang-fu organs and meridians, but also the basis for the analysis and research of the pathogenesis of various diseases.

The failure of qi activity refers to such pathological changes as qi stagnation, adverse flow of qi, qi sinking, qi blockage and qi exhaustion due to disturbance in its ascending, descending, exiting and entering. Ascending, descending, exiting and entering are the basic form of qi movement, on which functional activities of the zang-fu organs and meridians as well as the relationships between the zang-fu organs and meridians, qi and blood, and yin and yang depend to maintain their relative balance. For this reason, the disorder of qi activity may bring about various morbid conditions involving the zang-fu organs, qi and blood, yin and yang, exterior and interior, four limbs and nine orifices.

The disorder of blood includes deficient blood production, blood deficiency caused by massive hemorrbage, overconsumption of blood caused by prolonged illness, or dysfunction of blood nourishment; it also includes the accelerated blood circulation caused by blood heat and blood stasis caused by sluggish blood circulation. The metabolism of body fluid is essentially the processes of continuous production, distribution and excretion of body fluid.

The disturbance of the metabolism means the disturbance of distribution and the imbalance between production and excretion, thus causing deficiency production of body fluid to form fluid retention in the body. So, nornal metabolism of body fluid is the basic condition maintaining normal distribution, production and excretion. Normal production, distribution and excretion of body fluid are inseparable from ascending, descending, exiting and entering moverment of qi and its transforming function. And also, they cannot be separated from the functions of the lung, spleeni, liver, kidney and the triple energizer.

The five endogenous pathogens refer to the pathological changes caused by the dysfunction of qi, blood, body fluid and the zang-fu organs, namely endogenous wind, endogenous cold, endogenous dryness and endogenous fire. They are not pathogenic factors; rather, they are five comprehensive changes of pathogenesis.

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