The basic concept of body fluid
Body fluid is a basic substance that makes up the body and maintains life activities. The main component of body fluid is water, also including nutrient substance. Body fluid is also a component of blood when it flows inside the vessels. However, body fluid also flows outside the vessels in the viscera and the body. If secreting or excreting from the five sensory organs and the nine orifices, body fluid becomes urine, sweating, tears, snivel, saliva and drool, etc.
Body fluid can be divided into two parts: thin fluid and thick fluid which are different from each other in property, location and functions. Generally speaking, thin fluid flows quickly and is distributed in the skin, muscles and orifices to moisten the related parts of the body. The thick fluid relatively flows slowly and is distributed in the viscera, cerebral marrow and joints to nourish the related parts of the body. Though different in texture and distribution, both the thin and thick fluids come from food and water transformed by the spleen and stomach, functionally flowing inside and outside the vessels to permeate and supplement each other. Physiologically they are not strictly separated from each other; pathologically "impairment of the thin fluid" is relatively light while "loss of the thick fluid" is relatively serious.
The production of body fluid
The digestive and absorbing functions of the stomach, the spleen and the large and small intestines play a key role in the production of body fluid. Body fluid comes from food, especially water and liquid diet. The production of body fluid comes through a series of physiological activities, including the functions of the stomach to receive and digest, the functions of the spleen to transport, transform and transmit, the functions of the small intestine to receive and digest, and the functions of the large intestine to transmit and change. Different viscera may exert different effect on the water taken into the body. So the metabolism of body fluid is accomplished under the coordination of different viscera.
The physiological functions of body fluid
The physiological functions of body fluid includes the following three aspects.
1. Moistening and nourishing
Body fluid contains large quantity of water and nutrient substances to moisten and nourish the viscera and the body. To be specific, the thin fluid, distributed in the skin and orifices, mainly functions to moisten the body; the thick fluid, distributed in the viscera and cerebral marrow, mainly functions to nourish the body.
2. The transformation of blood
Body fluid not only flows outside the vessels, but also inside the vessels to participate in the production of blood. Blood is composed of two parts: body fluid and the nutri-ent qi. If body fluid is insufficient, the production of blood will be reduced, leading to blood deficiency.
3. The transportation of the turbid qi
Body fluid can hold various turbid qi and waste materials produced by qi-transformation and transport them to the concerned organs to be excreted out of the body through urination, sweating and respiration. The waste materials and the turbid qi are directly excreted in the form of fluid through urination and sweating. But the turbid qi excreted through respiration is transported to the lung first by body fluid and then exhaled out of the body. If body fluid is insufficient, the turbid qi cannot be quickly excreted out of the body, seriously affecting qi-transformation and causing various pathological changes.
The transportation and metabolism of body fluid
The transportation and metabolism of body fluid are complicated, involving the physiological activities of several viscera. Body fluid, produced by the spleen and the stomach to absorb water and nutrients from food, is transported to the heart and the lung by the spleen to start its metabolic process. The viscera concerned with the metabolism of body fluid mainly include the spleen, the lung and the kidney as well as the heart, the liver, the bladder, the large intestine and the triple energizer.
The spleen, the lung and the kidney play a key role in the transportation and diistribution of body fluid. The spleen, governing transportation and transformation, transports body fluid to the heart and the lung; the lung, governing the regulation of water passage, transports body fluid to the whole body and down into the kidney; the kidney, governing water and separating the clear from the turbid, again transports body fluid that is steamed and qi-transformed during the formation of urine into the heart and the lung. In propelling the circulation of blood, the heart also promotes the flow of body fluid.
In this way body fluid is transported to the whole body to nourish the five zang-organs and the six fu-organs. After being used, the rest of water and the waste metabolic materials are excreted out of the body through certain routes. The excretion of body fluid involves the lung, the kidney, the bladder and the large intestine. Lung-qi, governing dispersion, depuration and descent, excretes the fluid from the skin and respiratory tract and excretes the fluid together with feces from the large intestine. Kidney-qi, governing water, transforms the fluid into urine to be excreted as urine from the bladder. Among these different routes, urination and sweating are the major ones for the excretion of the fluid. Only part of the fluid is excreted through defecation and respiration.
Besides, the liver and the triple energizer also play a certain role in the distribution and excretion of body fluid. Liver-qi, governing dredging and dispersing, promotes the flow and metabolism of body fluid by means of regulating the activity of qi; the triple energizer, serving as a water passage, directs body fluid to flow downward through it to the kidney. In the whole process of the flow and metabolism of body fluid, the triple energizer, connecting the upper with the lower, participates in the whole process of the production, distribution and excretion of body fluid. To be specific, the upper energizer participates in the distribution of body fluid as implied in the idea that "the upper energizer is like fog";; the middle energizer participates in the absorption of body fluid as implied in the idea that "the middle energizer is like maceration"; the lower energizer participates in the excretion of body fluid as implied in the idea that "the lower energizer is like a sewer".
On the whole, the flow and metabolism of body fluid involve several viscera, but the lung, the spleen and the kidney are the most important ones. So the dysfunction or hypofunction of these three organs will affect the flow and metabolism of body fluid, leading to phlegm, retention of fluid and edema.
Appendix: The five zang-organs transforming five kinds of liquids
The five kinds of liquids include sweat, snivel, tear, saliva and drool. TCM believes that these liquids are transformed by the five zang-organs.
The relationships between the five zang-organs and the five kinds of liquids are described this way: sweat is the liquid of the heart, snivel is the liquid of the lung, tear is the liquid of the liver, saliva is the liquid of the spleen and spittle is the liquid of the kidney.
(1) Sweat comes from body fluid and is excreted out of the body through sweat pores under the steaming of yang-qi. The heart pertains to fire in the five elements. Heart-fire transforms into yang-qi to steam body fluid which comes out of the skin and becomes sweat. Thus sweat is regarded as the fluid of the heart. Insufficiency of heart-yang results in oligohidrosis while superabundance of heart fire brings on polyhidrosis.
(2) Snivel refers to the nasal mucus that can moisten the nostrils. Since the nose is the orifice of the lung, so snivel is the liquid of the lung. If lung-qi fails to disperse, the nose will become stuffy and running; if lung-heat impairs body fluid, the nose will be dry with scanty snivel.
(3) Tear comes from the eyes and can moisten the eyes. Since the eyes are the orifices of the liver, the tear is certainly the liquid of the liver. If there is wind-heat in the liver, the eyes will become tearing; if liver-yin is insufficient, the eyes will become dry because of scanty tear.
(4) Saliva refers to the thin part of the fluid in the mouth. It can promote the intake of food. Since the mouth is the orifice of the spleen, saliva is the liquid of the spleen. If the spleen is weak, there will be profuse of saliva running out of the mouth; if spleen-yin is insufficient, the mouth will be dry because of scanty saliva in the mouth.
(5) Drool refers to the thick part of the fluid in the mouth. Except with wetting and dissolution of food, making it easier to swallow, and the role of oral cleaning and protection, drool can nourish the Kidney-essence.