The Six Fu organs include: the Gallbladder, Stomach, Small Intestine, Large Intestine, Bladder, and San Jiao (Triple Burner). Their common physiological characteristic is the reception and transformation of food and fluids. In ancient times, the term “Fu” was written as “府,” which means a hollow place for storing items, allowing for both entry and exit. The primary physiological function of the Six Fu organs is “transformation and transportation,” indicating that their role is mainly to receive, digest, and transform food, existing in a continuous cycle of fullness and emptiness. The Six Fu organs do not store essence and qi. Food enters the body and is expelled through seven important gates, referred to as the “Seven Gates” in the “Nan Jing,” namely the lips, teeth, epiglottis, cardia, pylorus, ileocecal valve, and anus. The lips are the “Flying Gate,” indicating that they can open and close freely like a door; the teeth are the “Hinged Door,” which can guard the upper end of the digestive tract and chew food; the epiglottis is the “Inhalation Gate,” where the esophagus and trachea meet, serving as the entrance and exit for air; the cardia is the upper opening of the stomach, where food enters the stomach; the pylorus is the lower opening of the stomach, connecting to the small intestine; the ileocecal valve is where the small intestine meets the large intestine, preventing the flow of fine substances from the small intestine into the large intestine; the anus, also known as the “Spirit Gate,” is the final part of the digestive tract, responsible for expelling feces. Therefore, any pathological changes at any of the Seven Gates will affect the reception, digestion, absorption, and excretion of food.
(1) Gallbladder The gallbladder is attached to the liver and is a hollow sac-like organ. Its main physiological function is to store and excrete bile. Bile is produced in the liver and secreted by it. Once formed, bile flows into the gallbladder for storage. Bile is also known as “essence juice,” hence the gallbladder is referred to as the “Palace of Essence.” Bile is yellow-green and extremely bitter, playing a crucial role in digestion. After eating, bile is released into the intestines through the liver’s dispersing action, assisting the spleen and stomach in maintaining normal digestion. Due to the close relationship between the liver and gallbladder, if liver function is normal, bile production and excretion will be smooth, allowing for proper digestion. If the liver is diseased, it will affect bile production and excretion, leading to digestive dysfunction. For example, if gallbladder qi ascends, bile may rise, causing a bitter taste in the mouth; if bile excretion is obstructed and cannot smoothly enter the intestines, symptoms such as loss of appetite, abdominal distension, and loose stools may occur; gallbladder disease can also cause nausea and vomiting; if liver and gallbladder function is impaired, bile may overflow into the skin, resulting in jaundice; if bile stagnates and transforms into heat, damp-heat accumulation can further congeal bile into stones. Although the gallbladder is one of the Six Fu organs, it primarily stores essence juice and is a clean palace that does not directly receive food waste, distinguishing it from the other Fu organs, thus it is classified as a “Extraordinary Fu organ.” (2) Stomach The stomach is located below the diaphragm, with its upper opening called the cardia, connecting to the esophagus, and its lower opening called the pylorus, leading to the small intestine. The stomach is also known as the “Stomach Cavity,” divided into three parts: upper, middle, and lower. The upper part is called “Upper Cavity,” including the cardia; the lower part is called “Lower Cavity,” including the pylorus; the area between the upper and lower cavities is called “Middle Cavity,” which is the body of the stomach. The main physiological functions of the stomach can be summarized in two aspects: (1) It is responsible for receiving and digesting food. Food enters through the mouth, passes through the esophagus, and enters the stomach, which receives it, hence the stomach is also called the “Sea of Food and Fluids,” as the physiological activities of the body and the transformation of qi, blood, and fluids depend on the nutrition from food, thus the stomach is also referred to as the “Sea of Food Qi and Blood.” Therefore, if the stomach is diseased, it can easily affect its ability to receive food, leading to symptoms such as poor appetite and aversion to food. “Digesting” implies initial processing and digestion. Food in the stomach undergoes grinding and digestive actions, transforming it into chyme, which then moves down to the small intestine, laying the foundation for further digestion. The stomach’s reception and digestion work in conjunction with the spleen’s transportation function, referred to as “Stomach Qi.” “Human life is based on Stomach Qi;” “With Stomach Qi, there is life; without Stomach Qi, there is death.”
(2) It is responsible for descending and harmonizing. After food enters the stomach and undergoes digestion, it moves into the small intestine for further digestion and absorption, with the turbid parts descending into the large intestine to form feces for excretion. Thus, the stomach is said to govern descent and harmony. Descending turbid substances is a prerequisite for the stomach to continue receiving food. If the stomach does not harmonize and descend, food may stagnate, leading to symptoms such as stomach distension and pain, and loss of appetite. If stomach qi ascends, symptoms such as nausea, vomiting, belching, and hiccups may occur. Additionally, if stomach qi does not descend, it can also affect the spleen’s ability to raise clear qi. (3) Small Intestine The small intestine is located in the abdomen, connecting above to the pylorus and below to the ileocecal valve, where it meets the large intestine. The physiological functions of the small intestine can be summarized in two aspects: (1) It receives and holds food. Receiving means to hold substances in a vessel, i.e., to accept. The small intestine receives food that has been initially digested by the stomach, thus it serves as a vessel for the contents of the stomach. Food remains in the small intestine for a longer time to facilitate further digestion, allowing the food to transform into essence to nourish the entire body. If the small intestine’s function of receiving food is abnormal, it can lead to digestive and absorption issues, manifesting as abdominal distension, diarrhea, and loose stools. “Transforming” refers to the changes, digestion, and transformation of substances; the small intestine’s transforming function is to further digest and absorb the food that has been initially digested by the stomach. (2) It separates the clear from the turbid. The “clear” refers to various fine substances; the “turbid” refers to the residual waste after digestion. The small intestine’s function of separating the clear from the turbid specifically includes three aspects: First, it separates the digested food into two parts: fine substances and waste; second, it absorbs the fine substances and transports the waste to the large intestine; third, while absorbing the fine substances, the small intestine also absorbs a large amount of water, which is then excreted as urine through the bladder. Thus, the physiological function of the small intestine is crucial in the digestion of food. When the small intestine functions normally, the clear and turbid substances follow their respective paths, fine substances nourish the whole body, waste is sent down to the large intestine, and excess water is excreted through the bladder. If the small intestine is diseased, it can lead to digestive dysfunction, causing symptoms such as abdominal distension and pain, and can also affect urination and defecation, such as reduced urination and loose stools. In such cases, methods to promote urination and solidify stools are often employed, known as “promoting urination to solidify stools.” (4) Large Intestine The large intestine is also located in the abdomen, connecting above to the small intestine at the ileocecal valve, and its terminal end is the anus, also known as the “Spirit Gate.” The main physiological function of the large intestine is to conduct waste. The large intestine receives the food residue separated from the small intestine, absorbs excess water, and forms feces, which are then expelled through the anus. The smooth conduction of waste depends on the normal function of the large intestine, as well as the stomach’s ability to descend turbid substances, the lung’s ability to disperse qi, and the kidney’s ability to transform fluids. Therefore, if the large intestine is diseased, abnormalities mainly occur in fecal excretion, such as diarrhea or constipation. Additionally, diseases of the large intestine can also affect the stomach, lungs, and other organs, leading to dysfunction. (5) Bladder The bladder is located in the lower abdominal cavity, a sac-like organ situated below the kidneys and in front of the large intestine. It connects above to the kidneys via the ureters and below to the urethra, opening at the front of the perineum. Among the five zang and six fu organs, the bladder is the lowest, serving as a reservoir for excess fluids after metabolism. The main physiological function of the bladder is to store and excrete urine. The water consumed by the body is transformed into fluids through the combined actions of the lungs, spleen, kidneys, and other organs, distributing nourishment throughout the body. After the metabolism of fluids, the remaining liquid is transported through the pathways of the San Jiao to the kidneys and bladder, becoming urine, which is stored in the bladder. When the urine reaches a certain volume, the bladder opens under the kidney’s qi transformation, allowing for timely and voluntary excretion. The storage and excretion of urine by the bladder rely entirely on the kidney’s qi transformation function. The so-called bladder qi transformation actually belongs to the kidney’s vaporization and transformation. Bladder diseases mainly manifest as frequent urination, urgency, and pain during urination; or difficulty urinating, residual urine, or even urinary retention; or enuresis, and in severe cases, urinary incontinence.
(6) San Jiao (Triple Burner) San Jiao is a unique term in TCM’s organ theory, referring to the upper, middle, and lower Jiao, and is one of the Six Fu organs. Its meridians are closely related to the Pericardium meridian. Throughout history, there have been various interpretations regarding its form and substance, and a complete consensus has yet to be reached. However, there is a general agreement on its physiological functions. In terms of form, San Jiao is generally considered a large organ encompassing all internal organs, hence it is also called the “Lonely Palace.” The physiological functions of San Jiao can be understood from both a holistic and local perspective. From a holistic view, San Jiao governs all qi and is responsible for the qi transformation and movement of fluids in the body. (1) Governing all qi and overseeing the body’s qi dynamics and transformation. “All qi” refers to all forms of qi in the body, such as the qi of the zang-fu organs, meridian qi, respiratory qi, and nutritive and defensive qi. San Jiao’s governance of all qi indicates its close relationship with the physiological activities of all organs, meridians, and tissues. The reason San Jiao can govern all qi is primarily due to the source of Yuan Qi. Yuan Qi originates from the lower Jiao, derived from the kidneys and transformed from congenital essence. However, the movement of Yuan Qi can only be disseminated and reach the entire body through the pathways of San Jiao, thus stimulating and promoting the functional activities of various organs and tissues, which is why San Jiao plays a role in governing all qi. “Qi dynamics” refers to the movement of qi, manifested as the rise and fall of qi entering and exiting. San Jiao serves as the channel for the rise and fall of qi. “Qi transformation” refers to the complex changes of various substances, especially the reception, digestion of food and fluids, as well as the absorption of nutrients and the excretion of waste after metabolism. The qi transformation process is completed with the participation of multiple organs, and San Jiao plays a crucial role in this process. San Jiao is the pathway for the transformation of food and the excretion of waste, serving as the beginning and end of the movement of essence and qi throughout the body. Additionally, San Jiao facilitates the movement of Yuan Qi, serving as the power source for qi transformation, promoting the body’s metabolism. (2) It serves as a channel for the movement of fluids. San Jiao has the function of regulating the movement of fluids, serving as the pathway for the rise and fall of fluids, and is one of the organs involved in the regulation of fluid metabolism. As stated in the “Su Wen”: “San Jiao is the official of drainage, from which the water pathways emerge.” This indicates that the primary function of San Jiao is to complete the qi transformation process of body fluids, ensuring the smoothness of the water pathways. If San Jiao is diseased, qi dynamics may become obstructed, leading to stagnation of both qi and fluids, resulting in symptoms such as edema and ascites. In such cases, methods to promote the flow of San Jiao are often employed for treatment. (3) It indicates the three parts of the body and their respective physiological functions. In TCM theory, San Jiao is also a concept for dividing the body into regions: the area above the diaphragm is the upper Jiao, including the heart and lungs; the area below the diaphragm and above the navel is the middle Jiao, mainly including the spleen and stomach; the area below the navel is the lower Jiao, including the liver, kidneys, large and small intestines, bladder, and uterus. Although the liver is anatomically located in the middle Jiao, TCM considers the liver and kidneys to be of the same origin, with a close physiological and pathological relationship, thus both are classified as part of the lower Jiao. Since the upper, middle, and lower Jiao encompass different organs, their physiological functions also differ. (1) The upper Jiao is like mist. “Mist” refers to a diffused and vaporous state of the fine substances of food and fluids. The upper Jiao being like mist indicates its role in dispersing defensive qi, nourishing the skin, hair, and all internal organs and tissues. Therefore, the function of the upper Jiao is actually reflected in the qi transformation and distribution of the heart and lungs, relating to the distribution of nutritive and defensive qi, blood, and fluids. Thus, variations in the function of the upper Jiao mainly reflect abnormalities in heart and lung function, with treatment focusing on regulating the heart and lungs. (2) The middle Jiao is like fermentation. “Fermentation” here refers to the image of food undergoing digestion and fermentation. The middle Jiao being like fermentation indicates the transformation of fine substances by the spleen and stomach. The function of the middle Jiao mainly refers to the physiological functions of the spleen and stomach, such as the reception and digestion of food, absorption of nutrients, vaporization of body fluids, and transformation of fine substances into blood. In fact, the middle Jiao serves as the pivot for the rise and fall of qi, and the source of the generation of qi and blood. Therefore, the function of the middle Jiao is described as “like fermentation.” Variations in the function of the middle Jiao mainly reflect abnormalities in spleen and stomach function, with treatment focusing on regulating the spleen and stomach.
(3) The lower Jiao is like a drainage ditch. “Drainage ditch” refers to a channel for draining water. The lower Jiao governs the separation of clear from turbid and the excretion of urine and feces, a process that actually includes the functions of the kidneys, small intestine, large intestine, and bladder. Therefore, variations in the function of the lower Jiao mainly reflect abnormalities in kidney and bladder function, with treatment focusing on regulating the kidneys and bladder.
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