Body Fluids are called 'Jinye' in Chinese. This word is composed of two characters: 津 (Jin) meaning 'moist' or 'saliva' and 液 (Ye) meaning 'fluid', specifically fluids of living organisms (those found in fruits for instance). Thus 'Jinye' could be translated as 'organic fluids'.
It refers to all liquids in the body other than Blood and they're divided into two kinds. Jin are the clear, light and watery Fluids which flow easily and quickly with Defensive Qi in the Exterior pores, skin and muscles. They are under the control of the Lungs, which spread them to the skin all over the body, and the Upper Burner, which controls their transformation and movement towards the skin. Their function is to moisten and partially nourish the skin and muscles. They also become a component of Blood, helping to thin it and prevent its stagnation or coagulation. Jin manifests as sweat, tears, saliva and mucus.
Ye are the thick, heavy, turbid and dense Fluids which flow slowly with the Nutritive Qi in the Interior joints, viscera, bowels, brain and
bone marrow. They are controlled by the Spleen and Kidneys, which transform them, and the Middle and Lower Burner, which move and excrete them. Ye functions to moisten and nourish the joints, brain, bone marrow and spine.
Body Fluids are formed from what we eat and drink. The process of forming Body Fluids occurs through several refining stages. Each stage further separates the Fluids into pure and impure portions. Thus the saying that there is "pure within the impure" and "impure within the pure". The proper movement of pure and impure portions of Body Fluids primarily occurs through the transformative function of the Spleen.
The initial formation of Fluids begins in the Stomach where food and drink are digested. Through the transformative function of the Spleen, they are then separated into pure and impure portions. The pure, or clear, portion goes from the Spleen up to the Lungs, which disperses part of them to the skin and sends part of them down to the Kidneys. For this reason, the Lungs are called the "Upper Source of Water". The impure or dirty part, transformed by the Spleen, is sent down to the Small Intestine where it is again separated into pure and impure parts. The pure part is sent to the Bladder while the impure part goes to the Large Intestine. There some of the water is reabsorbed; thus the saying that "the Large Intestine promotes the formation of Body Fluids". The Bladder also separates the fluids it receives into pure and impure portions. The pure part flows upwards to the surface of the body where it forms sweat, while the impure portion flows downwards and is transformed into urine.
The transportation and distribution of Body Fluid is mostly accomplished by the Spleen. The Lungs disperse and descend downward to the Kidneys, which govern water metabolism. Further, the Triple Burner is the passage through which Jinye moves. The Liver's function of smoothing and regulating the flow of Qi and Blood also has a part in transporting and distributing Body Fluids. Because the Heart controls the circulation of Blood, and Fluids are a component of this, the Heart also has a role in their distribution. Through the interaction of all of these Organs, Body Fluids circulate to perform their various functions.
The excretion of waste and excessive water in the body occurs according to our physiological needs. Some is sent through the water regulating function of the Lungs to the body surface where it is turned into sweat. Some is changed into urine by the Kidneys' function of separating the clear from the turbid and removed by the Bladder's function of storing and excreting urine. Others are transformed into nasal mucus, saliva and tears and are removed from the nose, mouth and eyes by their corresponding Organs. Furthermore, exhaled air by the Lungs also takes away some moisture.
Of the three major Organs involved with Body Fluids, the Spleen is the most important. Because it begins the process of Fluid transformation, and regulates the direction of pure and impure Fluid transportation in all of its stages of production, the Spleen is intimately involved with water metabolism throughout the body.
This reminds us that the functions of the Chinese Organs occur throughout every cell of the body, not just in the 'Organ' itself as we are accustomed to thinking in the West. For this reason the Spleen is always treated in any type of disorders involving Body Fluids: it is irremediably intertwined with Fluids. Note that the Spleen in Western physiology is a lymphatic organ also involved with lymphatic fluids.
The Lungs are said to regulate the "water passages" of our bodies for two reasons. Firstly because they diffuse some of the pure part of the Fluids coming up from the Spleen to the space under the skin. Secondly because they descend the other pure portion of the Fluids down to the Kidneys and Bladder.
The Kidneys play a critical role in the physiology of Body Fluids.
Firstly part of the pure Fluids that the Kidneys receive from the Lungs are vaporized and sent back up to the Lungs to moisten them, thus preventing them from getting too dry.
Secondly the Kidneys and more particularly Kidney Yang plays a strong role in the transformation of Fluids. In particular:
The Triple Burner, which does not refer to a specific Organ but rather a coordinating function between all the other Organs, aids the transformation, transportation and excretion of Fluids in all of its stages throughout the body.
The Upper Burner is likened to a 'mist' since it assists the Spleen in directing the pure fluids upwards and the Lungs in dispersing them to the skin.
The Middle Burner is considered a 'bubbling cauldron' because it assists the Stomach in its digestive and churning functions and in directing the impure part downwards.
The Lower Warmer is compared to a 'drainage ditch' since here it aids the Kidneys, Bladder and Small Intestine in their function of transforming, separating and excreting Fluids.
Firstly, it is Qi that transforms, transports and secretes Fluids. Without this motivating force, Fluids accumulate and eventually stagnate in the body, causing a variety of diseases.
Secondly Qi also holds Fluids in their proper place, just as it holds Blood in the vessels. When Qi is Deficient, Fluids may leak out, resulting in symptoms such as profuse or spontaneous sweating (Lung Qi Deficiency), chronic vaginal discharge (Spleen Qi Deficiency) or urinary incontinence (Kidneys Qi Deficiency).
Thirdly Fluids are primarily developed through the Spleen and Stomach which are powered by Qi. When Qi is sufficient, the Spleen and Stomach function normally and Body Fluids are abundant. However, when Qi is Deficient, the Spleen and Stomach are weakened and Body Fluids in turn may become insufficient.
Lastly Body Fluids play a role in the transportation of Qi and any loss of Fluids may therefore damage Qi. Excessive vomiting, profuse sweating or prolonged diarrhea can cause a severe loss of Qi. In that case the person may suffer from cold limbs, pallor, dislike of cold, all symptoms of Yang Deficiency. This is because the fluids that form sweat in the space between skin and muscles are blended with Defensive Qi, and profuse sweating also causes a loss of Defensive Qi. Since Defensive Qi pertains to Yang, it is said in Chinese Medicine that 'Profuse sweating injures Yang'. Qi may also be consumed by excessive vomiting: hence the saying 'Persistent vomiting depletes Qi'.
There is a relationship of mutual nourishment and symbiosis between Body Fluids and Blood.
They both belong to Yin, and both are derived from Grain Qi. Fluids enter the blood vessels and become a part of Blood, while Blood extravasates out of the Blood vessels and turns into Fluids.
Fluids supplement and nourish Blood. The clearest part of Fluids enters into the process that creates Blood and is transformed into it, thus replenishing it. This is why a long term loss of Fluids can cause a Deficiency of Blood, as in excessive use of saunas or hot tubs, or chronic spontaneous sweating. Fluids also thin Blood so it doesn't coagulate or stagnate.
Blood also supplements and nourishes Fluids. If Blood becomes Deficient due to excessive or chronic loss of Blood, as in hemorrhage or chronic menorrhagia, Fluids can become depleted, leading to Dryness and further Blood Deficiency. This is why sweating and bleeding methods should never be used together. Concretely if a patient is bleeding or has severe Deficiency of Blood, sweating should not be induced. This is also why people with Blood Deficiency do not sweat easily.
The formation, distribution and excretion of Body Fluids is a complicated process requiring the coordination of many Organs. Thus, pathological changes in any of the Organs may affect the normal metabolism of Fluids, especially those of the Lungs, Spleen and Kidneys, since they are the key Organs involved in the metabolism of water.
Any disturbances in the transportation, distribution and excretion of Fluids may cause the stagnation of water. This manifests as Phlegm retention diseases and edema. On the other hand, pathological changes of Fluids also affect the functions of the Organs. For example, insufficient Fluids in the Lungs causes dry cough, while excessive Fluids in the Lungs can cause congestion with difficult breathing and cough.
An excess of Fluids is called 'Dampness', and is the same as the Damp Internal Pathological Influence. The most common characteristic is a feeling of heaviness of the body or head. Fluid (or Damp) diseases include edema, Phlegm retention diseases, lymphatic problems and general fluid and cellular metabolism issues which, when not properly functioning, can also give rise to tumors, cysts and cancers.
A lack of Fluids is also considered a Fluid imbalance (Deficiency), since the body requires a certain amount of lubrication for normal function of the respiratory, alimentary and reproductive systems. Fluid is necessary for proper joint lubrication as well as a moistener for the intestines to promote proper bowel function.
Phlegm, the other type of fluid imbalance, can collect in the joints, skin, channels or Organs causing diverse imbalances. It forms when the Spleen, Lungs or Kidneys are unable to perform their transforming, transporting or excreting functions properly. The congested Fluids then transform into Phlegm, causing further bodily dysfunction.
Fluids imbalances can be divided into three categories: a Deficiency of Fluids, edema, and Phlegm blockage. Fluid Deficiency usually relates to a Deficiency of Yin or Blood, while edema or Phlegm always involve the Spleen, as its Qi is in charge of transforming and transporting Body Fluids.