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The Six Fu Organs refer to the gallbladder (Dan), stomach (Wei), small intestine (Xiao Chang), large intestine (Da Chang), bladder (Pang Guang), and San Jiao (Triple Burner). Their common physiological function is to transport and transform substances, characterized by excretion without storage and solid yet not full. Food enters through the esophagus into the stomach, where it is processed and then passed to the small intestine. The small intestine separates the clear (essence and fluids) absorbed by the spleen and transported to the lungs, distributing it throughout the body to meet the needs of the organs and meridians; the turbid waste (dregs) is sent to the large intestine, where it is formed into feces for excretion. Waste fluids are transformed by the kidneys into urine, which is stored in the bladder for excretion. During the digestion, absorption, and excretion processes, food must pass through the seven crucial openings of the digestive tract, known as the Seven Openings, which include: “lips as the entrance, teeth as the door, epiglottis as the suction door, stomach as the entrance, the lower opening of the stomach as the pylorus, the junction of the large and small intestines as the gate, and the lower extreme as the exit, hence the term Seven Openings” (from Nanjing, Chapter 44).
The physiological characteristics of the Six Fu Organs involve receiving and transforming food and drink, with a tendency towards communication and downward movement. “The Six Fu Organs transport and transform substances without storing them, hence they are solid yet cannot be full. This is because when food enters, the stomach is full while the intestines are empty. When food descends, the intestines are full while the stomach is empty” (from Suwen, Chapter on the Distinction of the Five Organs). Each Fu organ must timely empty its contents to maintain smooth function and coordination, hence the saying “The Six Fu Organs function through communication and follow the principle of descent”. This emphasizes the importance of communication and descent; if either is excessive or insufficient, it indicates a pathological condition.
1. Gallbladder
The gallbladder is the foremost of the Six Fu Organs and belongs to the Extraordinary Organs. It is shaped like a pouch, resembling a suspended gourd, and is attached to the liver’s small lobe. The gallbladder is yang and belongs to wood, corresponding with the liver, which is yin and also belongs to wood. The gallbladder stores and excretes bile, governs decision-making, and regulates the qi of the organs.
(1) Anatomy of the Gallbladder
1. Anatomical Position: The gallbladder is connected to the liver, situated between the small lobe of the liver, and has meridians that interconnect with the liver.
2. Structural Characteristics: The gallbladder is a hollow, pouch-like organ that stores bile, a pure, clear, bitter, yellow-green fluid. Therefore, the gallbladder is referred to as the “Middle Pure Organ” (from Lingshu, Chapter on the Organs), “Clear Organ” (from Qianjin Yaofang), and “Middle Clear Organ” (from Nanjing, Chapter 35).
The anatomical structure of the gallbladder is similar to that of other Fu organs, thus it is one of the Six Fu Organs. However, due to its physiological characteristic of storing pure fluids, it also belongs to the Extraordinary Organs.
(2) Physiological Functions of the Gallbladder
It also interacts with the Five Zang Organs to store essence and qi.
1. Storage and Excretion of Bile: Bile, also known as “essence fluid” or “clear fluid”, originates from the liver. “The residual qi of the liver leaks into the gallbladder, accumulating to form essence” (from Mai Jing). Bile is formed and secreted by the liver, then stored and concentrated in the gallbladder, and through the gallbladder’s excretory function, it enters the small intestine. Bile “is formed by the qi transformation of the liver wood, and when food enters the small intestine, it fills up, pressing the gallbladder to release its fluid into the small intestine to dissolve food and facilitate the passage of dregs. If bile is insufficient, the essence is not differentiated, resulting in pale and clean feces without yellow” (from Nanjing Zhengyi). The liver and gallbladder both belong to the wood element, with one being yin and the other yang, complementing each other. “The gallbladder is the Fu organ of the liver, belonging to wood, governing the rise of clear and the descent of turbid, facilitating the middle earth” (from Yixue Jianeng). Thus, the gallbladder also has the function of excretion, but its excretion relies on the liver’s qi to perform its duties.
The bile stored in the gallbladder is excreted due to the liver’s excretory function, entering the intestines to promote the digestion of food. If the functions of the liver and gallbladder are abnormal, the secretion and excretion of bile will be obstructed, affecting the digestive functions of the spleen and stomach, leading to symptoms of poor appetite, abdominal distension, diarrhea, and other digestive disorders. If damp-heat accumulates in the liver and gallbladder, causing the liver to lose its excretory function, bile overflows and saturates the skin, resulting in jaundice, characterized by yellowing of the eyes, skin, and urine.
2. Governing Decision-Making: The gallbladder governs decision-making, referring to its role in the mental and cognitive processes of judgment and decision-making. The gallbladder’s role in decision-making is crucial for defending against and eliminating adverse effects of certain mental stimuli (such as shock and fear), maintaining and controlling the normal flow of qi and blood, and ensuring the coordination of the organs. Hence, it is said: “The gallbladder is the official of central justice, from which decisions are made” (from Suwen, Chapter on the Secret Classic of Linglan). Mental and psychological activities are related to the gallbladder’s decision-making function, which assists the liver’s excretion to regulate emotions. When the liver and gallbladder work in harmony, emotions are stable. A strong gallbladder qi can withstand intense mental stimuli with minimal impact and recover quickly. Therefore, it is said that “the qi of the gallbladder is strong, and evil cannot interfere”. Individuals with weak gallbladder qi are more susceptible to adverse effects from mental stimuli, leading to conditions such as timidity, fearfulness, insomnia, and vivid dreams, which can often be treated effectively by addressing the gallbladder.
3. Regulating the Qi of the Organs: The gallbladder works with the liver to assist in the excretion of qi, regulating the flow of qi, thus maintaining the balance and coordination of the organs internally and the muscles externally, allowing for smooth ascension and descent, and unimpeded circulation. When the gallbladder functions normally, the other organs are easily stabilized, hence the saying “All eleven organs depend on the gallbladder” (from Suwen, Chapter on the Six Sections of Organ Images). This means that “All eleven organs rely on the gallbladder qi for harmony” (from Zabing Yuanliu Xizhu). The human body is a system of ascending and descending qi transformation; when the liver qi is smooth, the qi of the organs ascends and descends in an orderly manner, with balanced yin and yang, and harmonious qi and blood. The gallbladder is a Fu organ, while the liver is a Zang organ; in the relationship between Zang and Fu, the Zang is primary and the Fu is secondary. Why is it said that “All eleven organs depend on the gallbladder” rather than “All eleven organs depend on the liver”? Because the liver is yin wood, while the gallbladder is yang wood, representing the lesser yang within the yang. “Yang is the correct, and yin is the master” (from Suwen, Chapter on the Separation of Yin and Yang). Yin is the foundation of yang, and yang governs yin; thus, the gallbladder, being yang wood, leads the liver, which is yin wood, hence the saying “All eleven organs depend on the gallbladder”.
In summary, “All eleven organs depend on the gallbladder” emphasizes that in cognitive activities, the liver governs deliberation while the gallbladder governs decision-making. The liver and gallbladder mutually support each other, but this does not imply that the gallbladder has the role of “the great master of the five Zang and six Fu organs”. The gallbladder’s decision-making must be guided by the heart to function normally.
(3) Physiological Characteristics of the Gallbladder
1. Gallbladder Qi Governs Ascension: The gallbladder is the lesser yang among the yang, embodying the wood virtue of the east, belonging to jia wood, and governing the ascending qi of the lesser yang in spring, hence it is said that gallbladder qi governs ascension. The gallbladder qi’s ascension reflects its nature of smoothness and is synonymous with the liver’s preference for smoothness and aversion to stagnation. Jiazi is the head of the five movements and six qi, corresponding to spring, and is the lesser yang among the yang. When the spring qi rises, all things are at peace, which is a natural law. The human body corresponds with heaven and earth; thus, the gallbladder governs jiazi, and its qi rises smoothly, allowing the qi of the organs to flow smoothly. The ascension of gallbladder qi, which is the rise of wood, signifies the smooth excretion of the qi of the organs. When the gallbladder qi rises normally, the qi of the organs ascends and descends normally, maintaining their physiological functions. Hence, it is said: “The gallbladder is the qi of the lesser yang in spring; when the spring qi rises, all things transform and stabilize, thus if the gallbladder qi does not rise, it leads to symptoms of nausea, intestinal obstruction, and more” (from Pigwei Lun, Chapter on the Transformation of Spleen and Stomach).
2. Preference for Calmness: Calmness refers to tranquility and stillness. The gallbladder is the organ of clarity, preferring calmness and disliking disturbance. When calm and free from disturbances, the gallbladder qi is neither rigid nor soft, embodying the gentle warmth of the lesser yang, thus fulfilling its proper function, and the bile is excreted in a timely manner, allowing for decision-making. If there is evil in the gallbladder, whether heat, dampness, phlegm, or stagnation, the gallbladder loses its clarity and calmness, losing its gentle and smooth nature, leading to symptoms such as bitter vomiting, restlessness, palpitations, insomnia, and even extreme fear as if one is being pursued. Clinically, the use of Wen Dan Tang to treat restlessness, insomnia, bitter vomiting, and palpitations aims to restore the gallbladder’s calm and gentle nature to regain its proper function.
2. Stomach
The stomach is the organ that holds food in the abdominal cavity. It is curved in shape, connecting above to the esophagus and below to the small intestine. It is responsible for receiving and processing food and drink, serving as the warehouse for the essence of food and drink, and the sea of qi and blood. The stomach, functioning through descent, is in harmony with the spleen, which is its counterpart. The stomach and spleen reside in the middle earth, but the stomach is dry earth and belongs to yang, while the spleen is damp earth and belongs to yin.
(1) Anatomy of the Stomach
1. Anatomical Position: The stomach is located below the diaphragm, in the upper part of the abdominal cavity, connecting above to the esophagus and below to the small intestine. The stomach cavity is referred to as the stomach cavity, divided into upper, middle, and lower parts: the upper part is the upper cavity, including the cardia; the lower part is the lower cavity, including the pylorus; the middle cavity is between the upper and lower cavities. The cardia connects to the esophagus, and the pylorus connects to the small intestine, serving as the passage for food and drink entering and exiting the stomach.
2. Structural Characteristics: The stomach has a curved shape, with a greater curvature and a lesser curvature. As stated in Lingshu, Chapter on the Flat Person’s Stomach: “It is curved, receiving food and drink, and its shape has a greater and lesser curvature”. Lingshu, Chapter on the Stomach and Intestines also states: “The stomach is curved and bent”.
(2) Physiological Functions of the Stomach
1. Stomach Governs the Reception of Food and Drink: Reception refers to the act of accepting and containing. The stomach governs reception, meaning it accepts and contains food and drink. When food enters through the mouth, it passes through the esophagus, is accepted and temporarily stored in the stomach; this process is called reception, hence the stomach is referred to as the “Great Warehouse” and “Sea of Food and Drink”. “What a person receives as qi is food, and what is poured into food is the stomach. The stomach is the sea of food and drink” (from Lingshu, Chapter on the Jade Plate).
“The stomach governs reception, thus it is the repository of the five grains” (from Leijing, Chapter on Organ Images). The physiological activities of the body and the generation of qi, blood, and fluids depend on the nutrition from food, hence the stomach is also called the sea of qi and blood. The stomach’s function of reception is the foundation of its function of processing food, and if the stomach has pathological changes, it will affect its reception function, leading to symptoms such as poor appetite, fullness and discomfort in the stomach cavity, etc.
The strength of the stomach’s reception function depends on the abundance of stomach qi, reflected in the ability to eat or not. If one can eat, the stomach’s reception function is strong; if one cannot eat, the stomach’s reception function is weak.
2. Stomach Governs the Processing of Food: Processing refers to the initial digestion of food in the stomach, forming chyme. The stomach’s processing function refers to its role in digesting food into chyme. “The middle jiao is in the stomach cavity, neither rising nor falling, and governs the processing of food” (from Nanjing, Chapter 31). The stomach receives food and drink from the mouth and allows it to stay in the stomach for a short time for initial digestion, relying on the stomach’s processing function to transform food into chyme. After initial digestion, the essence of the food is transported by the spleen to nourish the entire body, while undigested chyme descends into the small intestine, continuously renewing the digestive process of the stomach. If the stomach’s processing function is weak, it can lead to symptoms such as stomach pain and belching of foul-smelling food.
The stomach’s functions of reception and processing must be coordinated with the spleen’s transportation function to be completed smoothly. Hence, it is said: “The spleen is the earth (the earth is yin, while heaven is yang—author’s note). The spleen assists the stomach qi in processing food and drink; if the spleen qi does not circulate, the food in the stomach cannot be processed” (from Annotations on the Treatise on Cold Damage). The spleen and stomach work closely together, “The stomach governs reception, and the spleen governs transportation; one receives, and one transports” (from Jingyue Quanshu, Chapter on Diet), allowing food and drink to be transformed into essence, generating qi, blood, and fluids to nourish the entire body. Therefore, the spleen and stomach are referred to as the foundation of postnatal life and the source of qi and blood generation. The nutrition from food and the digestive function of the spleen and stomach are crucial for human life and health. Thus, it is said: “Humans rely on food and drink as their foundation; therefore, if one is deprived of food and drink, one dies” (from Suwen, Chapter on the Phenomena of Flat People).
Traditional Chinese Medicine places great importance on stomach qi, believing that “humans rely on stomach qi as their foundation”. When stomach qi is strong, all five Zang organs are flourishing; when stomach qi is weak, all five Zang organs are declining. With stomach qi, there is life; without stomach qi, there is death. The term stomach qi encompasses three meanings: first, it refers to the physiological functions and characteristics of the stomach. The stomach is the sea of food and drink, with the functions of reception and processing, as well as the characteristics of descent and communication. These functions and characteristics are collectively referred to as stomach qi. Since stomach qi affects the function of the entire digestive system, it is directly related to the source of nutrition for the entire body. Therefore, the abundance or lack of stomach qi is related to the life activities and survival of the human body, holding significant importance in the life activities of the human body. Thus, in clinical treatment, attention must always be paid to protecting stomach qi. Second, it refers to the reflection of the spleen and stomach functions in the pulse, which shows a relaxed and moderate pulse. Because the spleen and stomach have the important role of digesting food and absorbing the essence of food and drink to nourish the entire body, and the essence of food and drink is transported through the meridians, the abundance or lack of stomach qi can be reflected in the pulse. Clinically, the pulse of those with stomach qi is characterized by a relaxed and strong pulse, neither fast nor slow. Third, it generally refers to the essence qi of the human body. “Stomach qi is the qi of food, the qi of nourishment, the qi of movement, the qi of life, the clear qi, the defensive qi, and the yang qi” (from Pigwei Lun, Chapter on the Discussion of Spleen and Stomach Deficiency).
Stomach qi can be reflected in appetite, tongue coating, pulse, and complexion. Generally, normal appetite, normal tongue coating, a rosy complexion, and a relaxed and moderate pulse are considered signs of having stomach qi. Clinically, the presence or absence of stomach qi is often used as an important basis for judging prognosis; if there is stomach qi, there is life; if there is no stomach qi, there is death. The so-called protection of stomach qi actually means protecting the functions of the spleen and stomach. In clinical prescriptions, it is essential to remember “do not harm stomach qi”, otherwise, if stomach qi fails, all medicines will be ineffective.
(3) Physiological Characteristics of the Stomach
1. Stomach Governs Communication and Descent: The stomach’s governance of communication and descent is in contrast to the spleen’s governance of the rise of clear. The stomach’s governance of communication and descent refers to the characteristic of the stomach’s qi being smooth and descending. “When food is processed in the stomach, its dregs are transmitted from the stomach’s lower opening to the upper opening of the small intestine” (from Yixue Rumen, Chapter on the Organs). When food enters the stomach, after being processed and initially digested, it must descend into the small intestine, where the clear and turbid are separated; the turbid is then moved to the large intestine and transformed into feces for excretion, thus ensuring the state of alternation between fullness and emptiness in the stomach and intestines. This is accomplished through the smooth descending action of the stomach qi. Hence, it is said: “When food enters, the stomach is full while the intestines are empty; when food descends, the intestines are full while the stomach is empty” (from Suwen, Chapter on the Distinction of the Five Organs). “When the stomach is full, the intestines are empty; when the intestines are full, the stomach is empty; the more empty and full, the more qi ascends and descends” (from Lingshu, Chapter on the Flat Person’s Stomach). Therefore, the stomach values communication and descent, which must be smooth. The theory of organ images in Traditional Chinese Medicine summarizes the physiological functions of the entire digestive system through the rise and descent of the spleen and stomach. The stomach’s communication and descent also include the function of the small intestine transmitting food residues to the large intestine and the large intestine transforming dregs. The spleen should rise to be healthy, and the stomach should descend to be harmonious; when the spleen rises and the stomach descends, they coordinate with each other to complete the digestion and absorption of food.
The stomach’s communication and descent are prerequisites for the descent of turbid. Therefore, if the stomach loses communication and descent, symptoms such as poor appetite, fullness and pain in the stomach cavity, constipation, nausea, vomiting, belching, and other symptoms of stomach qi reversal may occur. The spleen and stomach reside in the center, serving as the pivot for the body’s qi to ascend and descend. Thus, if the stomach qi does not descend, it not only directly leads to disharmony in the middle jiao but also affects the communication and descent of the Six Fu Organs, potentially leading to various pathological changes.
2. Preference for Moisture and Aversion to Dryness: The preference for moisture and aversion to dryness refers to the stomach’s preference for moisture and dislike for dryness. The theory of qi movement in Traditional Chinese Medicine states that the six qi are divided into three yin and three yang, with wind governing the jueyin, heat governing the shaoyin, dampness governing the taiyin, fire governing the shaoyang, dryness governing the yangming, and cold governing the taiyang. The three yin and three yang qi are also divided into the five movements, with jueyin wind qi belonging to wood, shaoyin heat qi belonging to fire, shaoyang fire qi belonging to fire, taiyin damp qi belonging to earth, yangming dry qi belonging to metal, and taiyang cold qi belonging to water. “Above the yangming, dryness governs” (from Suwen, Chapter on the Great Discussion of the Heavenly Origin), which refers to the division of the six qi into yin and yang, indicating that dryness governs the yangming, referring to qi movement. The human body corresponds with heaven and earth; in the human body, the yangming refers to the yangming meridian, which includes the foot yangming stomach meridian and the hand yangming large intestine meridian. Both the stomach and large intestine are endowed with dry qi, “The human body is endowed with the dry qi of heaven and earth, hence there are the stomach and large intestine, both of which are repositories for the digestion and transportation of food and drink; it is due to the endowment of dry qi that when water enters, it is digested and expelled, not allowed to remain in the stomach” (from Annotations on the Treatise on Cold Damage, Volume 2). Fire is dry, and water is moist; the yangming dry earth must rely on the taiyin damp earth to assist it, thus achieving the balance of water and fire, allowing the stomach to receive, process food, and descend turbid. Therefore, it is said: “The stomach and large intestine, in heaven, correspond to the shen and you, with shen belonging to the earth and you belonging to metal, in the four seasons, correspond to the seventh and eighth months, being the time for the use of dry metal”. Heaven and earth are merely the transformation of the two qi of water and fire; when water and fire intersect, they steam and become damp, and the interaction of damp and dryness is the qi of unchanging water and fire. If fire does not steam water, clouds and rain do not come; if water does not assist fire, dew does not fall.
In summary, the stomach’s preference for moisture and aversion to dryness is primarily reflected in two aspects: first, “the stomach, being a yang body, combines with yin essence; the yin essence descends” (from Four Sacred Heart Sources). The stomach’s descent of qi relies on the nourishment of stomach yin; second, the stomach’s preference for moisture and aversion to dryness corresponds with the spleen’s preference for dryness and aversion to dampness, allowing for the dynamic balance of the spleen’s ascent and the stomach’s descent.
3. Small Intestine
The small intestine resides in the abdomen, connecting above to the pylorus and communicating with the stomach, and below to the large intestine, including the ileum, jejunum, and duodenum. It is responsible for receiving, processing substances, and separating clear from turbid. It is related to the heart, belonging to fire and yang.
(1) Anatomy of the Small Intestine
1. Anatomical Position: The small intestine is located in the abdomen, with its upper end connecting to the pylorus of the stomach and its lower end connecting to the large intestine at the ileocecal junction, serving as the organ for further digestion of food. The small intestine has meridians that connect with the heart, thus they are interrelated.
2. Structural Characteristics: The small intestine is a hollow tubular organ that is coiled and looped. “The small intestine is attached behind the spine, looping around and coiling, with its connection to the ileum (which is the large intestine) located externally above the navel, with sixteen loops” (from Lingshu, Chapter on the Stomach and Intestines).
The small intestine includes the ileum, jejunum, and duodenum.
(2) Physiological Functions of the Small Intestine
1. Governing Reception and Transformation: The small intestine’s function of governing reception and transformation refers to its role in receiving and transforming food. Reception refers to the acceptance of the food that has descended from the stomach, serving as a container; transformation refers to the further digestion and absorption of the food into nutrients that can be utilized by the body, with the essence being absorbed and the dregs being sent to the large intestine. In pathology, if the small intestine’s reception function is disordered, the transmission and transformation will stop, leading to stagnation and pain, manifesting as abdominal pain. If the transformation function is abnormal, it can lead to digestive and absorption disorders, presenting as abdominal distension, diarrhea, and loose stools.
2. Governing Separation of Clear and Turbid: Separation refers to the process of distinguishing between the clear and turbid. The small intestine is responsible for separating the clear essence from the turbid waste during the further digestion of food. The clear essence, including the fluids transformed from beverages and the essence from food, is absorbed and then transported by the spleen to the heart and lungs, nourishing the entire body. The turbid waste is transmitted through the ileocecal junction to the large intestine, forming feces for excretion through the anus; the remaining water is transformed through the kidneys and enters the bladder, forming urine, which is excreted through the urethra. “The bladder and kidneys are interrelated, both governing water; water enters the small intestine, descends to the bladder, and is processed into urine” (from Zhubing Yuanhou Lun, Chapter on Various Lin Syndromes). Because the small intestine participates in the metabolism of body fluids during the separation of clear and turbid, it is said that “the small intestine governs fluids”. Therefore, Zhang Jingyue stated: “The small intestine is located below the stomach, receiving the water and grains from the stomach and separating the clear from the turbid; the fluids are absorbed and the dregs are sent down, with the spleen transforming and ascending, and the small intestine transforming and descending, hence the transformation of substances occurs” (from Leijing, Chapter on Organ Images).
When the small intestine’s function of separating clear and turbid is normal, the fluids and dregs follow their respective paths, and normal urination and defecation occur. If the small intestine’s function is disordered, leading to a failure to separate clear and turbid, the fluids may mix with the dregs, resulting in symptoms such as mixed food and liquid, loose stools, and diarrhea. Since “the small intestine governs fluids”, a dysfunction in the small intestine’s separation of clear and turbid can affect both bowel movements and urination, leading to reduced urination. Therefore, in the early stages of diarrhea, the method of “promoting urination to solidify the stool” is often used for treatment.
The small intestine’s functions of reception and transformation, as well as separation of clear and turbid, are the most important stages in the entire digestive process. During this process, the chyme is further digested, transforming food into clear (essence containing fluids) and turbid (dregs containing waste fluids) parts, with the former relying on the spleen’s transport to be absorbed and the latter descending into the large intestine. The digestive and absorption functions of the small intestine are often categorized within the scope of the spleen and stomach’s functions in the theory of organ images. The functions of the spleen and stomach in receiving and transporting actually encompass all aspects of modern digestive physiology and part of nutritional physiology. Hence, it is said: “Humans receive food and drink; the spleen transforms the essence qi upwards, while the small intestine transforms the dregs and transmits them downwards to the large intestine” (from Yiyuan).
What is referred to as “the spleen transforms the essence qi upwards” actually pertains to the small intestine’s functions of digestion and absorption. Therefore, conditions of poor digestion and absorption in the small intestine fall within the category of spleen dysfunction, often treated from the perspective of the spleen and stomach.
(3) Physiological Characteristics of the Small Intestine
The small intestine possesses the physiological characteristics of ascending clear and descending turbid: the small intestine transforms substances and separates clear from turbid, allowing the essence to ascend and the dregs to descend into the large intestine. The ascent and descent are interdependent, and the small intestine is responsible for receiving and transforming substances. If the ascent and descent are disordered, it can lead to symptoms such as vomiting, abdominal distension, and diarrhea. The small intestine’s function of ascending clear and descending turbid is a concrete manifestation of the spleen’s ascent of clear and the stomach’s descent of turbid.
4. Large Intestine
The large intestine resides in the abdomen, with its upper opening at the ileocecal junction connecting to the small intestine and its lower end connecting to the anus, including the colon and rectum. It is responsible for the transmission and transformation of dregs and the absorption of fluids. It belongs to metal and is yang.
(1) Anatomy of the Large Intestine
1. Anatomical Position: The large intestine is also located in the abdominal cavity, with its upper segment referred to as the ileum (corresponding to the anatomical ileum and the upper segment of the colon); the lower segment is referred to as the descending colon (including the sigmoid colon and rectum). Its upper opening connects to the small intestine at the ileocecal junction, and its lower end connects to the anus (also referred to as the lower extreme or exit gate). The large intestine is connected to the lungs through meridians, thus they are interrelated.
2. Structural Characteristics: The large intestine is a tubular organ, presenting a coiled and looped structure.
(2) Physiological Functions of the Large Intestine
1. Transmission of Dregs: The large intestine’s function of transmission refers to its role in receiving the food residues that descend from the small intestine, forming feces for excretion through the anus. The large intestine receives the food residues from the small intestine, absorbs the remaining water and nutrients, forming feces for excretion, representing the final stage of the entire digestive process, hence it is referred to as the “transmitting organ” and “transmitting official”. Therefore, the primary function of the large intestine is to transmit dregs and excrete feces. The large intestine’s transmission function is closely related to the stomach’s descent, the spleen’s transportation, the lung’s descending function, and the kidney’s storage function.
If the large intestine is diseased, the transmission will be abnormal, primarily manifesting as changes in the quality and quantity of feces and alterations in the frequency of bowel movements. If the large intestine’s transmission is abnormal, it can lead to constipation or diarrhea. If damp-heat accumulates in the large intestine, causing qi stagnation, it can lead to symptoms such as abdominal pain, urgency, and dysentery with pus and blood.
2. Absorption of Fluids: After the large intestine receives the food residues and remaining water from the small intestine, it reabsorbs some of the fluids, forming feces for excretion. The large intestine’s function of reabsorbing fluids participates in regulating the body’s fluid metabolism, referred to as “the large intestine governs fluids”. The large intestine’s ability to reabsorb fluids is related to the metabolism of fluids in the body. Therefore, the large intestine’s pathological changes are often associated with fluids. If the large intestine is deficient and cold, it will be unable to absorb fluids, leading to mixed food and liquid, resulting in symptoms such as bowel sounds, abdominal pain, and diarrhea. If the large intestine is in a state of excess heat, it will consume fluids, leading to dry intestines and constipation. The majority of the water required by the body is absorbed in the small or large intestine, hence “the large intestine governs fluids, and the small intestine governs liquids; both the large and small intestines receive the nourishing qi from the stomach, allowing them to transport fluids to the upper jiao, irrigating the skin and nourishing the pores” (from Pigwei Lun, Chapter on the Discussion of the Five Zang Organs).
(3) Physiological Characteristics of the Large Intestine
In the functional activities of the organs, the large intestine is constantly receiving the food residues that descend from the small intestine, forming feces for excretion, demonstrating a state of accumulation and transmission coexisting, solid yet not full, thus it functions through descent and communication. The Six Fu Organs function through communication and descent, especially the large intestine. Therefore, the smooth descent and communication of the large intestine is an important physiological characteristic. If the large intestine’s communication and descent are abnormal, leading to internal accumulation of dregs, it is often said that “the intestines are prone to fullness”.
5. Bladder
The bladder, also known as the clean organ, water repository, jade sea, urinary bladder, is located in the lower abdomen, positioned at the lowest part among the organs. It is responsible for storing and excreting urine, interrelated with the kidneys, belonging to the water element, and its yin-yang attribute is yang.
(1) Anatomy of the Bladder
1. Anatomical Position: The bladder is located in the lower abdomen, beneath the kidneys and in front of the large intestine. It is positioned at the lowest part among the organs.
2. Structural Characteristics: The bladder is a hollow, pouch-like organ. It has ureters above, connecting to the kidneys, and below, it has a urethra that opens at the front, referred to as the urinary opening.
(2) Physiological Functions of the Bladder
1. Storing Urine: In the process of fluid metabolism in the body, fluids are distributed throughout the body through the actions of the lungs, spleen, and kidneys, playing a role in moistening the body. After being utilized by the body, the remaining fluids descend to the kidneys. Through the kidneys’ qi transformation, the clear is returned to the body, while the turbid is sent to the bladder, transforming into urine. Therefore, it is said: “The remaining fluids enter the bladder to become urine”, and “urine is the residue of fluids” (from Zhubing Yuanhou Lun, Chapter on Bladder Syndromes), indicating that urine is transformed from fluids. The relationship between urine and fluids is often interdependent; if fluids are deficient, urine will be scant; conversely, if urine is excessive, it can lead to fluid loss.
2. Excreting Urine: When urine is stored in the bladder and reaches a certain capacity, through the qi transformation of the kidneys, the bladder opens and closes appropriately, allowing urine to be expelled from the urinary opening in a timely manner.
(3) Physiological Characteristics of the Bladder
The bladder possesses the physiological characteristic of governing opening and closing. The bladder is the repository for the body’s fluids, hence it is referred to as the “organ of fluids” and “the official of the state”. The bladder relies on its opening and closing function to maintain the coordinated balance of urine storage and excretion.
The kidneys and bladder are interrelated, opening at the two yin; “the bladder is the official of the state, storing fluids; when qi transforms, it can be expelled. However, if the kidney qi is sufficient, it transforms; if the kidney qi is insufficient, it does not transform. If the qi does not transform, the water returns to the large intestine, causing diarrhea. If the expelling qi does not transform, it leads to obstruction in the lower jiao, resulting in urinary retention. The smoothness of urination is governed by the bladder, while the kidney qi governs it” (from Bi Hua Yi Jing). The bladder’s functions of storing and excreting urine rely entirely on the kidneys’ functions of solidification and qi transformation. The so-called bladder qi transformation actually belongs to the kidneys’ qi transformation. If the kidneys’ functions of solidification and qi transformation are abnormal, the bladder’s qi transformation will be disordered, leading to symptoms such as difficulty urinating or urinary retention, as well as frequent urination, urgency, incontinence, and other issues, hence it is said: “If the bladder is not functioning properly, it leads to urinary retention; if it is not controlled, it leads to incontinence” (from Suwen, Chapter on the Discussion of the Five Qi).
6. San Jiao (Triple Burner)
San Jiao is a unique term in the theory of organ images. San Jiao refers to the upper, middle, and lower burners, collectively known as one of the Six Fu Organs, and is the largest of the Fu organs, also referred to as the outer Fu or lonely organ. It governs the rise and fall of qi and the circulation of fluids, belonging to the fire element and having a yang attribute.
(1) Anatomy of the San Jiao
Historically, there has been a debate regarding the anatomical form of the San Jiao, with some asserting it is “named but formless” while others argue it is “named and formed”. Even among those who believe it has form, there is still no unified view on its essence. However, there is basic agreement on the understanding of the physiological functions of the San Jiao.
As one of the Six Fu Organs, the San Jiao is generally considered to be a large organ distributed within the thoracic and abdominal cavities, being the largest and unmatched, hence referred to as the “lonely organ”. As Zhang Jingyue stated: “The San Jiao is indeed a Fu organ, located outside the Zang organs but within the body, encompassing all the organs, a large organ” (from Leijing, Chapter on Organ Images).
Regarding the form of the San Jiao, as an academic issue, it can be further explored; however, this issue is not the main focus of the theory of organ images itself. This is because the concept of organs in Traditional Chinese Medicine differs from the anatomical concept of organs; the classification of the San Jiao as a separate Fu organ is not solely based on anatomy but is more importantly established based on the connections of physiological and pathological phenomena.
In summary, the upper jiao is above the diaphragm, including the heart and lungs; the middle jiao is from the diaphragm to the navel, including the spleen and stomach; the lower jiao is from the navel to the two yin, including the liver, kidneys, large and small intestines, bladder, and uterus. Although the liver is anatomically located in the middle jiao, due to its close relationship with the kidneys, both the liver and kidneys are classified under the lower jiao. The functions of the San Jiao actually encompass the overall functions of all the Zang and Fu organs.
(2) Physiological Functions of the San Jiao
1. Transporting Yuan Qi: Yuan qi (also known as original qi) is the fundamental qi of the human body, originating from the kidneys, transformed from congenital essence, and nourished by postnatal essence, serving as the foundation of yin and yang in the organs and the original driving force of life activities. Yuan qi is distributed to the five Zang and six Fu organs through the San Jiao, nourishing and invigorating the functions of each organ. Therefore, it is said that the San Jiao is the channel for the movement of yuan qi. The movement of qi is a fundamental characteristic of life. The San Jiao’s ability to transport yuan qi relates to the qi transformation of the entire body. Hence, it is said: “The San Jiao is the qi of the three yuan, governing the five Zang and six Fu organs, regulating the qi of the internal and external, upper and lower, and left and right” (from Zhizhi Yao). When the San Jiao is open, the internal and external, upper and lower are all open.
2. Regulating Water Pathways: “The San Jiao is the official of drainage, from which the water pathways emerge” (from Suwen, Chapter on the Secret Classic of Linglan). The San Jiao can “regulate the water pathways” (from Yixue Sanzi Jing), playing an important role in controlling the entire process of fluid metabolism in the body. The metabolism of body fluids involves multiple organs working together in a complex physiological process. Among them, the upper jiao’s lungs serve as the source of water, promoting the distribution and regulation of water; the middle jiao’s spleen and stomach transform and distribute fluids to the lungs; the lower jiao’s kidneys and bladder vaporize and transform fluids, allowing them to ascend to the spleen and lungs, participating in metabolism, and then forming urine for excretion. The San Jiao serves as the pathway for the generation, distribution, and movement of water and fluids. The qi transformation of the San Jiao ensures that the meridians are open and the water pathways are smooth. The San Jiao’s role in maintaining the balance of water metabolism is referred to as “San Jiao qi transformation”. The San Jiao’s function of transporting water and fluids is essentially a summary of the functions of the lungs, spleen, kidneys, and other organs involved in fluid metabolism.
3. Transporting Food and Drink: “The San Jiao is the pathway for food and drink” (from Nanjing, Chapter 31). The San Jiao has the function of transporting food and drink, assisting in the distribution of essence and the excretion of waste. The upper jiao “opens up to receive the flavors of the five grains, nourishing the skin and muscles” (from Lingshu, Chapter on Qi Decision), thus having the function of distributing essence; the middle jiao “separates the dregs, steams the fluids, and transforms the essence, ascending to the lung meridians” (from Lingshu, Chapter on the Regulation of Qi), thus serving the purpose of digestion and absorption; the lower jiao “forms dregs and sends them down to the large intestine, following the lower jiao to enter the bladder” (from Lingshu, Chapter on the Regulation of Qi), thus serving the purpose of excreting feces and urine. The San Jiao’s function of transporting food and drink is a summary of the functions of the spleen and stomach, liver and kidneys, heart and lungs, and the large and small intestines in completing the digestion, absorption, and excretion of food and drink.
(3) Physiological Characteristics of the San Jiao
1. Upper Jiao as Mist: The upper jiao as mist refers to the upper jiao’s role in distributing defensive qi and nourishing essence. The upper jiao receives the essence of food and drink from the middle jiao’s spleen and stomach, distributing it through the heart and lungs to nourish the entire body, akin to the nourishing effect of mist. Hence, it is said that “the upper jiao is like mist”. Because the upper jiao receives essence and distributes it, it is also referred to as “the upper jiao governs reception”.
2. Middle Jiao as Fermentation: The middle jiao as fermentation refers to the spleen and stomach’s role in transforming food and drink into qi and blood. The stomach receives and processes food and drink, and through the spleen’s transformation, the essence of food is formed into qi and blood, which is then transported upwards to nourish the heart and lungs. Because the spleen and stomach have the physiological function of processing food and transforming essence, it is likened to “the middle jiao is like fermentation”. The middle jiao governs the transformation of food and drink.
3. Lower Jiao as Drainage: The lower jiao as drainage refers to the kidneys, bladder, large and small intestines’ role in separating clear from turbid and excreting waste. The lower jiao transmits the food residues to the large intestine, transforming them into feces for excretion, and the remaining fluids are transformed into urine through the kidneys and bladder, which is then excreted. This physiological process has a downward and outward draining effect, hence it is said that “the lower jiao is like drainage”. Because the lower jiao facilitates the excretion of waste, it is also referred to as “the lower jiao governs excretion”.
In summary, the San Jiao is related to the reception, digestion, absorption, and excretion of food and drink, encompassing the entire qi transformation process. Therefore, the San Jiao serves as the channel for transporting yuan qi and food and drink, representing a comprehensive function of the physiological functions of the Zang and Fu organs.
