1. The Concept of Body Fluids
Body fluids refer to all normal fluids in the human body. They include the normal bodily fluids and secretions of various organs, such as gastric juice, intestinal fluid, saliva, and synovial fluid. Habitually, they also include metabolic byproducts like urine, sweat, and tears. Thus, it is said: “Sweat and urine can both be referred to as body fluids, as they are essentially water” (from “Essays on Medicine: Theories of Qi, Blood, and Spirit”). Body fluids are primarily composed of water and contain a large amount of nutrients, serving as the fundamental substances that constitute the human body and maintain life activities. “Human beings are endowed with the dual energies of Yin and Yang, having both clear and turbid aspects. The clear aspect of Yang is the original Qi, while the turbid aspect is fire; the clear aspect of Yin is body fluids, and the turbid aspect is phlegm” (from “Luo’s Medical Mirror”).
Within the body, all normal fluids, except for blood, fall under the category of body fluids.
Body fluids are widely present in organs, tissues, and between tissues, playing a role in nourishing and moistening. Additionally, body fluids can carry Qi, allowing Qi to circulate throughout the body and exert its physiological effects. Body fluids are also one of the material bases for the generation of blood and are closely related to the production and circulation of blood. Therefore, body fluids are not only the basic substances that constitute the human body but also the fundamental materials that sustain life activities.
Although both body fluids and liquids belong to the category of water, they differ in properties, functions, and distribution. Generally speaking, fluids that are clear, thin, and highly mobile, primarily distributed in the skin, muscles, and orifices, and that permeate the blood vessels to provide moisture, are referred to as body fluids; those that are thicker, less mobile, and permeate the joints, organs, brain, and marrow to provide nourishment are referred to as liquids: “Body fluids and liquids each have their own pathways, thus the San Jiao (Triple Burner) releases Qi to warm the muscles and fill the skin, which is its body fluid; what flows but does not move is liquid” (from “The Spiritual Pivot: Differentiation of Body Fluids”).
2. The Metabolism of Body Fluids
(1) The Generation of Body Fluids
The generation, distribution, and excretion of body fluids is a complex physiological process involving multiple organs and a series of physiological activities.
“When ingested into the stomach, it flows and overflows with essence, is transported to the spleen, where the spleen Qi disperses the essence, then returns to the lungs, regulating the water pathways, and is finally excreted through the bladder, with the essence of water distributed throughout the five meridians” (from “The Yellow Emperor’s Classic of Medicine: Discussion on Meridians”) summarizes the metabolic process of body fluids.
Body fluids originate from food and are generated through the digestion and absorption of water and nutrients in the food by the spleen, stomach, small intestine, and large intestine. The specific process is as follows:
The spleen and stomach digest and transform food into the sea of water and grains, primarily receiving and absorbing the essence of food through the overflow of Qi. “When water enters the stomach, its essence is scattered throughout the organs and meridians, thus becoming body fluids” (from “Essays on Medicine: Dryness and Dampness as Similar Diseases”). The spleen governs transformation and transportation, relying on the ascending function of spleen Qi to transport the essence and body fluids absorbed from the stomach and intestines to the heart and lungs, and then distribute them throughout the body. Thus, it is said: “Body fluids and Qi are transported by the heart, passing through the lungs, filling the skin, and dispersing throughout the hundred vessels” (from “The Treatise on the Spleen and Stomach: Discussion on Spleen and Stomach Strength and Weakness”).
The small intestine governs liquids, separating the clear from the turbid, absorbing most of the nutrients and water from food, transporting them to the spleen, distributing them throughout the body, and sending metabolic byproducts through the kidneys to the bladder, while excreting waste through the large intestine.
The large intestine governs body fluids, receiving the food residues and remaining water from the small intestine, reabsorbing some of the water to form feces for excretion. The large intestine participates in the generation of body fluids through its governing function.
The generation of body fluids is primarily led by the spleen, with the participation of the stomach, small intestine, and large intestine, but it is also related to other organs.
In summary, the generation of body fluids depends on two main factors: first, sufficient water-rich foods, which serve as the material basis for generating body fluids; second, the normal functioning of the organs, especially the spleen, stomach, and intestines. Any abnormality in either factor can lead to insufficient generation of body fluids, resulting in pathological changes due to body fluid deficiency.
(2) The Distribution of Body Fluids
The distribution of body fluids primarily relies on the comprehensive functions of the spleen, lungs, kidneys, liver, heart, and San Jiao.
The heart governs the blood vessels: “The middle Jiao (Middle Burner) steams the essence of water and grains, transforming it into blood, which circulates through the meridians” (from “Classifications of the Lushan Hall: Differentiation of Blood”). “When body fluids are harmonized, they transform and become blood” (from “The Spiritual Pivot: Abscesses and Sores”). The heart, associated with fire, is the supreme Yang, governing the blood vessels of the entire body. Body fluids and blood rely on the heart’s Yang energy to circulate normally, continuously.
The spleen Qi disperses essence; the spleen governs the transformation of the essence of water and grains. Through its transport function, it transports body fluids to the lungs, where the lungs’ dispersing and descending functions distribute body fluids throughout the body, nourishing the organs, tissues, and orifices. Additionally, it can directly distribute body fluids to all parts of the body, as the spleen has the function of “irrigating the surroundings”; it is said that “the spleen governs the transportation of body fluids from the stomach” (from “The Yellow Emperor’s Classic of Medicine: Discussion on Syncope”).
The lungs govern the movement of water, regulating the water pathways and serving as the upper source of water. After receiving the body fluids transported from the spleen, the lungs distribute them to the upper body and surface through their dispersing function, and to the kidneys and bladder as well as the lower body through their descending function.
The kidneys govern body fluids: “The kidneys are the water organ, governing body fluids” (from “The Yellow Emperor’s Classic of Medicine: Discussion on Reversal Regulation”). The kidneys play a dominant role in the distribution of body fluids, primarily in two aspects: first, the Yang energy in the kidneys promotes the vaporization and transformation of body fluids, which is driven by the functions of the stomach’s “overflowing essence,” the spleen’s dispersing essence, the lungs’ regulation of water pathways, and the small intestine’s separation of clear from turbid. Second, the body fluids that descend from the lungs to the kidneys undergo vaporization in the kidneys, where the clear is vaporized and transported through the San Jiao to the lungs and distributed throughout the body, while the turbid is transformed into urine and injected into the bladder.
The liver governs the smooth flow of Qi, ensuring the smooth operation of Qi mechanisms, which in turn promotes the circulation of body fluids.
The San Jiao governs the drainage: The San Jiao is the “drainage organ,” where Qi is the mother of water; Qi can transform water and distribute body fluids. The San Jiao has the function of regulating and draining water, serving as the channel for the flow and distribution of body fluids within the body.
Although the distribution of body fluids is closely related to all five organs, it is primarily accomplished by the spleen, lungs, kidneys, and San Jiao. The spleen transports the body fluids from the stomach and intestines to the lungs, where the lungs, through their dispersing and descending functions, allow the body fluids to reach the skin and nourish the organs, distributing them throughout the body.
(3) The Excretion of Body Fluids
The excretion of body fluids, like their distribution, primarily relies on the comprehensive functions of the lungs, spleen, kidneys, and other organs. The specific excretion pathways are as follows:
Sweat and exhalation: The lung Qi disperses, distributing body fluids to the skin, where they are vaporized by Yang energy to form sweat, which is excreted through the sweat pores. The lungs govern respiration, and during exhalation, they also carry away some body fluids (moisture).
Urine is the final product of body fluid metabolism. Its formation is closely related to the lungs, spleen, kidneys, and other organs, but especially to the kidneys. The vaporization function of the kidneys, in conjunction with the bladder’s vaporization function, jointly forms urine for excretion. The kidneys play a key role in maintaining the balance of body fluid metabolism, hence it is said: “Water is the ultimate Yin, its source is in the kidneys.”
Feces: The feces formed from the residues of food and water excreted by the large intestine also carry away some body fluids. During diarrhea, the feces contain a lot of water, leading to a significant loss of body fluids, which can easily cause body fluid injury.
In summary, the physiological process of body fluid metabolism requires the comprehensive regulation of multiple organs, particularly the lungs, spleen, and kidneys. Thus, it is said: “Water is the ultimate Yin, hence its source is in the kidneys; water transforms in Qi, hence its manifestation is in the lungs; water fears earth, hence its regulation is in the spleen” (from “Complete Works of Jingyue: Swelling”). If the functions of these three organs are disordered, it can affect the processes of generation, distribution, and excretion of body fluids, disrupting the balance of body fluid metabolism, leading to insufficient generation of body fluids, circulatory obstruction, stagnation of water, or excessive loss of body fluids. Among these, the function of the kidneys is the most critical. Thus, it is said: “The kidneys are the water organ, governing body fluids” (from “The Yellow Emperor’s Classic of Medicine: Discussion on Reversal Regulation”). Insufficient generation of body fluids or excessive loss leading to dryness can result in Yin fluid deficiency, even leading to the loss of fluids and Yin. The treatment should focus on nourishing fluids, generating body fluids, nourishing Yin fluids, and consolidating fluids to rescue Yin. When body fluids accumulate, they can lead to dampness, phlegm, water retention, and other pathological changes, and treatment should focus on inducing sweating, transforming dampness, promoting urination, expelling water, and resolving phlegm.
3. The Functions of Body Fluids
The functions of body fluids primarily include nourishing and moistening, generating blood, regulating Yin and Yang, and excreting waste.
(1) Nourishing and Moistening
Body fluids, primarily composed of water, have a strong nourishing effect and are rich in various nutrients. The quality of body fluids is the lightest and clearest, while liquids are clear and crystalline, thick and cohesive. Among essence, blood, body fluids, and liquids in the body, blood is the most abundant, essence is the heaviest, while the utility of body fluids is the greatest. Internally, they nourish the organs and bones, and externally, they nourish the skin and hair. All rely on body fluids for nourishment. “Body fluids are transformed from water and grains; the turbid part becomes blood, while the clear part becomes body fluids, nourishing the organs, muscles, and meridians, allowing Qi and blood to circulate smoothly without stagnation. There can be no Qi and blood without this; without this, they become dry and stagnant… Liquids are thick and do not flow with Qi; they are also transformed from water and grains, stored between joints and tendons, facilitating movement. The fluids that exit through orifices are called tears and saliva, all of which belong to this category” (from “Essays on Medicine: Theories of Qi, Blood, and Spirit”). The body fluids distributed on the surface can nourish the skin, warm the muscles, making them plump and the hair glossy; the body fluids within can nourish the organs, maintaining their normal functions; the body fluids entering the orifices can moisten the mouth, eyes, nose, and other nine orifices; the body fluids flowing into the joints can warm and benefit the joints; the body fluids penetrating into the marrow can nourish the bone marrow and brain marrow.
(2) Generating Blood
Body fluids penetrate into the blood vessels, becoming one of the basic components for generating blood. Body fluids fill the blood and nourish and lubricate the blood vessels, allowing blood to circulate continuously. Thus, it is said: “The middle Jiao releases Qi like dew, which flows into the valleys and permeates the vessels; body fluids harmonize and transform into blood” (from “The Spiritual Pivot: Abscesses and Sores”). “Water nourishes the meridians, and thus blood is formed” (from “The Treatise on the Spleen and Stomach: Discussion on Medication Indications and Contraindications”).
(3) Regulating Yin and Yang
Under normal circumstances, the Yin and Yang in the human body are in a relatively balanced state. Body fluids, as part of Yin essence, play an important role in regulating the balance of Yin and Yang in the body. The normalcy of the Yin of the organs is closely related to the abundance or deficiency of body fluids. The human body maintains a normal state in response to physiological conditions and changes in the external environment through the self-regulation of body fluids. For example, in cold weather, the sweat pores of the skin close, preventing body fluids from being excreted as sweat, leading to increased urination; in hot summer, excessive sweating reduces body fluids, leading to decreased urination. When the body loses water, it increases water intake to replenish body fluids. “Water and grains enter through the mouth, are transported to the intestines and stomach, and their liquids are differentiated into five; in cold weather, they become urine and Qi, while in hot weather, they become sweat” (from “The Spiritual Pivot: Differentiation of Body Fluids”), thus regulating the balance of Yin and Yang in the body, maintaining normal life activities.
(4) Excreting Waste
During the metabolism of body fluids, they can continuously excrete metabolic byproducts from the body through sweat, urine, and other means, ensuring the normal Qi transformation activities of the organs. If this function is impaired or obstructed, metabolic byproducts can accumulate in the body, leading to various pathological changes such as phlegm, fluid retention, water, and dampness.
4. The Five Organs and Body Fluids
(1) The Concept of the Five Organs and Body Fluids
The five secretions or excretions, namely sweat, nasal mucus, tears, saliva, and spittle, are referred to as the five fluids. The five fluids are generated by the five organs: the heart produces sweat, the lungs produce nasal mucus, the liver produces tears, the spleen produces saliva, and the kidneys produce spittle. The five fluids are generated by the five organs and belong to them, hence they are called the five organs and body fluids, also known as the five organs and five fluids.
(2) The Relationship Between the Five Organs and the Five Fluids
The five fluids belong to the category of body fluids, all generated from body fluids, distributed within the orifices of the five organs, playing roles in nourishing, moistening, and regulating body fluid metabolism. The generation, distribution, and excretion of the five fluids occur during the vaporization process of body fluids, resulting from the comprehensive actions of multiple organs, particularly the lungs, spleen, and kidneys. However, the five organs are the core of the organ theory, thus sweat, nasal mucus, tears, saliva, and spittle are classified according to the five organs. Thus, it is said: “In a person’s body, there are nasal mucus, tears, saliva, spittle, feces, and urine, all belonging to the transformation of one water, and emitted through the nine orifices” (from “Record of Questions”). “Sweat and urine can both be referred to as body fluids” (from “Essays on Medicine: Theories of Qi, Blood, and Spirit”). The relationship between the five organs and the five fluids represents the unity of overall regulation and local regulation in the process of body fluid metabolism.
1. Sweat is the fluid of the heart: What is sweat? “Yang added to Yin is called sweat” (from “The Yellow Emperor’s Classic of Medicine: Discussion on Yin and Yang”). “Yang” refers to the Yang energy within the body; “Yin” refers to the Yin fluids within the body. The phrase “Yang added to Yin is called sweat” means that sweat is the body fluids transformed from Yin fluids through the vaporization of Yang energy, excreted from the sweat pores. The secretion and excretion of sweat also rely on the opening and closing of the defensive Qi on the skin. When the pores are open, sweat is excreted; when the pores are closed, there is no sweat. Since sweat is transformed from body fluids, and blood and body fluids originate from the same source, there is a saying that “sweat and blood share the same source.” Blood is governed by the heart, and sweat is the fluid of blood, vaporized into sweat, hence it is called “sweat is the fluid of the heart.” As Li Zhongzi said: “What the heart stores internally is blood, while what is emitted externally is sweat; sweat is the fluid of the heart” (from “Essential Readings in Medicine: Sweat”). Due to the close physiological relationship between sweat and blood, they also influence each other pathologically. In terms of the relationship between sweat and blood, excessive sweating can deplete blood and injure body fluids. Conversely, deficiency of body fluids leads to reduced blood. Thus, in clinical practice, when blood deficiency symptoms appear, caution should be exercised in using sweating methods. The principle of “depleting blood leads to no sweat, and depleting sweat leads to no blood” is based on this. Regarding the relationship between sweat and the heart, excessive sweating can deplete the heart’s Qi and blood, leading to symptoms such as palpitations and anxiety. Since sweating is the result of the evaporation of body fluids due to Yang energy, excessive sweating can also harm the Yang energy, leading to critical conditions of Yang loss. Conversely, when the heart’s Qi and blood are insufficient, it can also cause pathological sweating, such as spontaneous sweating due to heart Qi deficiency or night sweats due to heart Yin deficiency.
2. Nasal mucus is the fluid of the lungs: Nasal mucus is the secretion of the nose, which has the function of moistening the nasal orifices. The nose is the orifice of the lungs, and among the five organs that generate fluids, the lungs produce nasal mucus. When the lung’s physiological function is normal, nasal mucus moistens the nasal orifices without flowing out. If the lungs are affected by wind-cold, clear nasal mucus may flow; if affected by wind-heat, turbid nasal mucus may flow; if the lungs are dry, there may be little or no nasal mucus.
3. Saliva is the fluid of the spleen: Saliva is the oral fluid, and the clearer part of saliva is called saliva. Saliva has the function of protecting and cleaning the oral cavity. During eating, saliva is secreted in larger amounts, moistening and dissolving food, making it easier to swallow and digest. Under normal circumstances, saliva rises in the mouth but does not overflow. If the spleen and stomach are not harmonious, it often leads to a rapid increase in saliva secretion, resulting in excessive salivation, hence it is said that the spleen governs the fluid of saliva.
4. Tears are the fluid of the liver: The liver opens to the eyes, and tears flow from the eyes. Tears have the function of moistening and protecting the eyes. Under normal circumstances, the secretion of tears is moistening and does not overflow, but when foreign objects invade the eyes, tears can be secreted in large amounts to clean the eyes and expel foreign objects. In pathological conditions, abnormal secretion of tears can be observed. For example, insufficient liver Yin and blood can lead to reduced tear secretion, often resulting in dry eyes; if there is wind-heat in the liver meridian, it can lead to increased tear secretion and tearing in response to wind. Additionally, in cases of extreme sorrow, tear secretion can also increase significantly.
5. Spittle is the fluid of the kidneys: Spittle, like saliva, is oral fluid. The thicker part is called spittle, while the thinner part is called saliva. The fluid of the spleen is saliva, while the fluid of the kidneys is spittle. In addition to moistening and dissolving food, making it easier to swallow, and cleaning and protecting the oral cavity, spittle also nourishes kidney essence: since spittle is transformed from kidney essence, excessive spittle or prolonged spitting can easily deplete kidney essence, which is why practitioners often swallow spittle to nourish kidney essence.
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