The six fu-organs refer to the gallbladder, the stomach, the small intestine, the large intestine, the bladder and the triple energizer. The common physiological function of the six fu-organs is "to transmit and transform food", i.e. receiving and digesting food, absorbing the nutrients and excreting the waste. Since the six fu-organs should be clear in order to transmit and transform food, it is said that "the six fu-organs function to descend" and "the six fu-organs function well if they are unobstructed".
The gallbladder is connected with the liver and contains bile. The bile comes from the liver and is the accumulation of the surplus part of liver-qi. The bile is yellow in color and bitter in taste, playing an important role in assisting the absorption of food. That is why the bile is called "the essential juice" or "the lucid juice" and the gallbladder is called "the fu-organ of essential juice"; or "the fu-organ of lucid juice" in TCM.
The physiological function of the gallbladder is to store and excrete the bile. The gallbladder itself is empty. After produced by the liver, the bile is stored in the gallbladder and directed by the dredging and dispersing functions of the liver, excreted into the small intestine to participate in the process of digestion and absorption of food and promote the small intestine to separate the lucid from the turbid.
Whether the excretion of the bile is normal or not is concerned with the dredging and dispersing functions of the liver on the one hand and the unobstructed condition of the gallbladder on the other. Failure of the liver to dredge and disperse or obstruction of the gallbladder itself will affect the excretion of the bile and disturb digestion and absorption, frequently leading to anorexia, abdominal distension, vomiting, hypochondriac pain or even jaundice if the bile is extravasated in the muscles and skin.
The stomach is connected with the esophagus in the upper and the small intestine in the lower, usually divided into three parts, namely shangwan (the upper part of the stomach and cardia), zhongwan (the middle part of the stomach) and xiawan (the lower part of the stomach and pylorus) .
The physiological function of the stomach is to receive and digest food. The chyme transformed in the stomach is then transmitted to the small intestine. Since the stomach is big and can contain large amount of food, it is called "the sea of food and water" in Huangdi Neijng.
The stomach depends on the stomach-qi to perform its function. Stomach-qi is the basic motive power for transmitting food and water in the stomach downwards. The canal connecting the stomach and the small intestine must be kept unobstructed so that the chyme can smoothly be transmitted from the stomach to the small intestine. That is why the physiological function of the stomach is often described as "the stomach functions to descend" and "the unobstructed condition is prerequisite to the normal function of the stomach" in TCM, usually abbreviated as "the stomach governing descent". Dysfunction of the stomach will lead to distending stomachache and poor appetite due to disharmony of stomach-qi, or belching, vomiting, nausea and hiccup due to failure of stomach-qi to descend or upward flow of stomach-qi.
Since the food received and digested by the stomach is the main substance for producing qi and blood, the stomach is called "the sea of food".
The small intestine
The small intestine is located in the middle of the abdomen, connected with the stomach at the pylorus in the upper and the large intestine at ileocecal junction in the lower. The physiological function of the small intestine is to receive the chyle and separate the lucid from the turbid.
1. To receive the chyle
The small intestine receives the chyme from the stomach and keeps for a certain period of time in order to further digest it.
2. To separate the lucid from the turbid
The lucid refers to food nutrients and the turbid refers to the waste of food. After further digestion absorption of the nutrients and part of the water, the small intestine transmits the waste to the large intestine. This process is called "to separate the lucid from the turbid" in TCM.
In fact, to receive the chyme and to separate the lucid from the turbid are two aspects in the digesting and absorbing process. There is a close relationship between these two aspects. The former is the condition of the latter and the latter is the result of the former.
TCM emphasizes the functions of the five zang-organs, so the digesting function of the small intestine is attributed to the transporting and transforming function of the spleen. If the small intestine is normal in absorbing water, then the stool will appear normal form and the urination will be smooth. If the small intestine is abnormal in absorbing water and the water is kept in the intestines and moves downward with the waste, then the stool will be sloppy and the urine will become scanty. Such a condition is usually differentiated as "dysfunction of the spleen". If the small intestine absorbs too much water, the urine will become profuse and the stool will become retained. Such a condition is called "constipation due to spleen deficiency and scanty fluid", indicating the relationship between the small intestine and the spleen. Clinically diarrhea in some cases is treated by the therapy "for promoting urination to consolidate the stool", focusing on promoting urination to reinforce the function of the small intestine to absorb water. The syndrome of "constipation due to spleen deficiency and scanty fluid" can be treated by slowing down the descending activity to reduce the speed of the small intestine in absorbing water.
The large intestine
The large intestine is connected with the small intestine in the upper and the anus in the lower. The physiological function of the large intestine is mainly to receive the waste of food transmitted down from the small intestine. After absorbing part of the water in it, the large intestine transmits the waste downward and transforms it into stool to be excreted from the anus.
The function of the large intestine to transmit the waste of food is described in Huangdi Neijing as "transmission and excretion", the activities of which are accomplished by the propelling function of the large intestinal qi. If the large intestine is abnormal in function, it will lead to constipation due to improper transmission and diarrhea due to insufficient absorption of water.
The bladder, located in the lower abdomen, is responsible for storing and discharging urine.
The water and turbid qi produced in the process of metabolism are changed into urine through qi-transforming function of the kidney and transmitted to the bladder. When certain amount of urine is accumulated in the bladder, it is excreted naturally out of the body through the action of qi-transformation. The storage and excretion of urine by the bladder result from the fixating and qi-transforming functions of qi. Since bladder-qi is controlled by the kidney-qi, the fixating and qi-transforming functions of kidney-qi is key to the storage of urine in the bladder and excretion of urine out of the bladder. Generally speaking, failure of kidney-qi to fixate and transform qi due to deficiency affects the function of the bladder to excrete urine. If the bladder is attacked by exogenous pathogenic factors, qi-transformation activity will be affected, also leading to disorder in excreting urine. But the syndrome in the former case is deficiency and the syndrome in the latter case is excess. Deficiency of bladder-qi usually leads to symptoms of polyuria, enuresis and incontinence of urine. Obstructed transformation of qi often brings on dysuresia.
The triple energizer
The triple energizer is composed of three parts, i.e. the upper energizer, middle energizer and lower energizer. The diaphragm and the navel are regarded as the lines to divide the triple energizer. The part above the diaphragm is the upper energizer, the part below the diaphragm and above the navel is the middle energizer, and the part below the navel is the lower energizer. The upper energizer includes the thorax, the heart and the lung; the middle energizer includes the upper abdomen, the spleen, the stomach, the liver, the gallbladder and the small intestine; the lower energizer includes the lower abdomen, the kidney, the bladder and the large intestine.
The physiological function of the triple energizer
The triple energizer is an independent functional system which is based on the morphological structure of the internal organs and tissues. In fact it is a generalization of the physiological functions of the internal organs. The physiological functions of the triple energizer include the following two aspects:
1. A generalization of yuan-qi (primordial qi) and water passage
The triple energizer serves as a transmitting system, through which substances like the primordial qi and water are transported and transmitted.
The primordial qi, the root source of qi, comes from congenital essence and nourishes the acquired base of life. It is the primary motivation of life activity. The primordial qi originates from the kidney and, through the transportation and transmission of the triple energizer, is distributed to all parts of the body for warming and nourishing the viscera and the tissues so as to activate and promote the physiological functions of the other viscera and tissues. If the primordial qi is deficient and the transportation of the triple energizer is not smooth, it will lead to qi deficiency in certain areas in the body.
When taken into the stomach and transported and transformed by the spleen, the water is transmitted upwards to the lung which, by means of regulating the water passage, transmits the water downwards to the kidney. The kidney separates the lucid from the turbid with its function of transforming qi. Such a continuous circulation maintains normal metabolism of water inside the body. The lung is located in the upper energizer, the spleen in the middle energizer and the kidney in the lower energizer. It is the triple energizer that organizes these three organs into a system for transmitting and metabolizing water. That is why triple energizer is regarded as a very important passage of water. If the triple energizer is obstructed, the functions of the lung, the spleen and the kidney will certainly be affected, leading to oliguria and edema.
2. A generalization of the physiological functions of certain internal organs
The generalization of the physiological functions of certain viscera with the triple energizer is mainly concerned with the digestion and absorption of food, distribution of food nutrients and metabolism of water. Huangdi Neijing used three similes to describe the functions of the triple energizer: the upper energizer is like fog, the middle energizer is like maceration and the lower energizer is like sewer.
(1) The upper energizer is like fog:
The heart and the lung are located in the upper energizer. This simile describes the functions of the heart and the lung to distribute essence. That is to say that the function of the heart and the lung to distribute food nutrients is just like fog permeating everywhere. When exogenous pathogenic factors invade the upper energizer, it not only affects the dispersion and distribution of essence, but also leads to the symptoms of dysphoria, palpitation, cough and chest oppression due to dysfunction of the heart and lung.
(2) The middle energizer is like maceration:
This simile describes the digestion and absorption of food by the spleen and the stomach. In fact the digestion and absorption of food are not only related to the spleen and the stomach, but also to the liver and the gallbladder. The stomach governs reception and digestion of food; the spleen governs transportation and transformation of food nutrients; the liver and the gallbladder smooth the activity of qi, excrete the bile and promote digestion. Since the spleen, the stomach, the liver and the gallbladder are located in the upper abdomen, this simile is actually a generalization of the digesting and absorbing functions of these organs. If pathogenic factors are retained in the middle energizer, the digesting and absorbing functions will be affected, leading to distending fullness of the upper abdomen, vomiting, diarrhea and jaundice.
(3) The lower energizer is like sewer:
This simile describes the functions of the kidney and the bladder that move the turbid liquid downward and discharge it out of the body. This is in fact a generalization of the functions of the kidney and the bladder in producing and excreting urine. If pathogenic factors invade the lower energizer, the excretion of urine will be affected, leading to oliguria, frequent urination, urgent urination and pain in urination.