The zang-fu theory explains the physiological function, pathological changes, and mutual relationships of every zang and fu organ. In traditional Chinese medicine the zang and fu organs are not simply anatomical substances, but more importantly represent the generalization of the physiology and pathology of certain systems of the human body.
Zang and fu consist of the five zang and six fu organs. The five zang organs are the heart (including the pericardium), lung, spleen, liver, and kidney. The six fu organs are the gall bladder, stomach, large intestine, small intestine, urinary bladder and the sanjiao (three areas of the body cavity). Zang and fu are classified by the different features of their functions. The five zang organs mainly manufacture and store essence: qi, blood, and body fluid. The six fu organs mainly receive and digest food, absorb nutrient substances, transmit and excrete wastes. As the Suwen says: The five zang organs store up essential qi and regulate its outflow. The six fu organs transform and transport substances without storing them and for this reason they may be over-filled but cannot be filled to capacity.
There is another category of organs called the extraordinary fu organs which include the brain, marrow, bone, vessels, gall bladder, and uterus. They are named fu but their functions are similar to that of the five zang organs. Since their physiological functions and pathological changes are closely connected with the zang-fu organs they will be discussed below under the specific zang or fu organ.
The Five Zang Organs include: Heart, Lung, Spleen, Liver, and Kidney.
The Six Fu Organs
The gall bladder is attached to the liver and stores bile. There is an ancient saying regarding the close relationship between the liver and bile, "The remaining qi of the liver flows to the gall bladder and turns into the juice of essence (bile)." Bile is continuously excreted into the intestinal lumen to assist in digestion. The bitter taste and yellow color of bile are significant in disease manifestations of bitter taste in the mouth, vomiting of bile, jaundice, etc. As the liver and the gall bladder are externally and internally related, the gall bladder is also involved in the free flow of qi concerning emotional activities.
Clinically, when some mental disorders or emotional symptoms such as fear and palpitation, insomnia, dream disturbed sleep, etc. occur, treatment can be applied by considering the gall bladder.
Situated below the diaphragm, the stomach's upper outlet connects with the esophagus, and its lower outlet with the small intestine. Its main physiological function is to receive and digest food. The stomach is also known as the "sea of water and cereal." Food is digested here, then sent downward to the small intestine, where the essential substances are transformed and transported by the spleen to the whole body. The spleen and the stomach collectively are known as the "acquired foundation," that is, their proper nourishment establishes the foundation for a healthy life. Clinical diagnosis and treatment place great stress on the strength and weakness of the stomach and spleen qi. Generally, it is considered that whatever kind of disease occurs, if stomach qi is still strong, the prognosis will be good. It is said, "Stomach qi is the foundation of the human body. When there is stomach qi, there is life. When there is no stomach qi death will follow." Preserving stomach qi is therefore considered an important principle of treatment.
Normal stomach qi descends. If it fails to descend, symptoms such as anorexia, fullness, pain and distension of the upper abdomen, nausea, vomiting, hiccough, etc. will appear.
The upper end of the small intestine connects with the stomach, its main function being to receive partially digested food from the stomach and further divide it into clear and turbid. The small intestine transfers the turbid residues to the large intestine. The spleen transports the clean essential substances to all parts of the body, and part of the water contained in food to the urinary bladder. Therefore, if diseased, the small intestine will not only affect the function of digestion and absorption, but also lead to urinary problems.
The upper end of the large intestine is connected to the small intestine by the ileocecum, and its lower end connects to the anus. Its main physiological function is to receive the waste material send down from the small intestine and, in the process of transporting it to the anus, absorb a part of its fluid, and convert it into feces to be excreted from the body. Dysfunction of the large intestine produces the symptoms of borborygmus and diarrhea; if the fluid is further exhausted, the symptoms will be constipation and so on.
The main function of the urinary bladder is to store and discharge urine. It has an exterior and interior relationship with the kidney. Pathologically, if the urinary bladder has a dysfunction of qi, dysuria or retention of urine will appear. If its restrictive function is lost, there may be excessive urination or incontinence of urine.
Sanjiao (three areas of the body cavity) is a general term for the three sections of the body trunk. The upper jiao contains the heart and lung, the middle jiao contains the spleen and stomach, and the lower jiao contains the kidney and urinary bladder. The following are the categories of function as described by the Lingshu:
The function of the upper jiao is to act like a fog; the function of the middle jiao is maceration; the function of the lower jiao is to be an aqueduct.
Thus the heart and lung function is to distribute qi and body fluid by a spreading and moistening action. The spleen and stomach must digest, absorb, and transfer the qi, blood, and body fluid transformed from the essential substances; a similar process to that of soaking in water to cause decomposition and dissolution. The kidney and urinary bladder function to transport fluids and water. Pathological problems in any of the three jiao will effect the organs located there.