The relationship between qi and body fluid is similar to the relationship between qi and blood, because body fluid is a component of blood. Besides, body fluid exists not only in the vessels, but also in all the tissues and organs in the body. In this sense, the relationship between qi and body fluid differs in some way from the relationship between qi and blood.

The effect of qi on body fluid is demonstrated in three aspects: qi producing body fluid, qi promoting the flow of body fluid and qi controlling body fluid.

Body fluid comes from the water and nutrients of food transformed by the spleen and stomach. The spleen and stomach play an important role in the production of body fluid. If spleen-qi and stomach-qi are sufficient and if the digesting and absorbing functions are normal, the transformation and production of body fluid will be sufficient; if spleen-qi and stomach-qi are deficient and if the digesting and absorbing functions are abnormal, the transformation and production of body fluid will be reduced.

The flow of body fluid, including the distribution and excretion, depends on the propelling function of qi. At the early stage body fluid is transported by spleen-qi to the heart and the lung; heart-qi propels body fluid and blood to flow; lung-qi disperses the fluid in the skin and viscera on the one hand, and descends the fluid to the kidney and the bladder on the other; the kidney and the bladder, through @transformation, transports the lucid part of the fluid to the heart and the lung on the one hand, and descends the turbid part of the fluid to transform it into urine to be discharged out of the body on the other. 

Since the flow and metabolism of body fluid all depend on the propelling and transforming functions of qi, the state of qi and the activity of qi directly affect the flow and metabolism of body fluid. If qi deficiency or qi stagnation occurs, the fluid will accumulate and turn into phlegm and edema. That is why it is said in TCM that "normal flow of qi ensures normal flow of water and stagnation of qi leads to stagnation of water."

Under the propelling and transforming action of qi, the metabolism of the body is demonstrated in two ways: opening and closing. Opening means to excrete the remaining part of fluid out of the body and closing means to keep certain amount of water needed in the body. The way that qi keeps body fluid in the body is called "qi controlling body fluid". The ways to excrete water from the body include urination and sweating. If qi fails to control body fluid due to deficiency, it will lead to abnormal urination and sweating, such as poliguria, incontinence of urine, enuresis and polyhidrosis, etc.

Body fluid is the carrier of qi and qi must attach itself to body fluid in order to flow to the whole body. This theory can be understood from two angles. On the one hand, blood produced by body fluid in the vessels can carry the nutrient qi; on the other hand, body fluid flowing in other tissues and organs can carry the defensive qi. If great quantity of body fluid is lost, qi will be exhausted accordingly. This state is called "loss of body fluid followed by exhaustion of qi". In severe cases, it will become "loss of body fluid followed by loss of qi".

     

Body fluid, just like blood, can produce qi. On the one hand, body fluid inside the vessels transforms into blood to nourish the viscera so as to maintain sufficiency of qi in these viscera and the body. On the other hand, body fluid outside the vessels nourishes the muscles and orifices to maintain their normal functions. At the same time body fluid outside the vessels keeps a constant communication with body fluid inside the vessels and supplements each other. If body fluid becomes deficient, its function to nourish and moisten will be weakened, leading to decline of visceral qi.