In general, zang organs mainly manufacture and store essential substances like blood, qui, essence, and body fluid while fu organs receive, digest, transport, and excrete. Organ manifestation (Zang Xiang) theory was developed because of rich experience, clinical practice, and anatomical knowledge of ancient Chinese doctors and because of pathological and physiological observations.
The heart, as the “supreme ruler”, distributes blood and dominates the blood vessels. Blood is also the material basis for mental activities and thinking, so the heart is also said to house the mind and spirit and is associated with the emotion of joy. The health of the heart can be seen in the tongue, taste, and speech. The peri-cardium functions to protect the heart.
If the heart dominates the blood, then the liver stores and regulates the volume of blood. It also maintains the free flow of qi given its elemental properties (wood), so a normally functioning liver creates harmonious qi and blood which helps balance emotions. Additionally, the liver supports digestion with the excretion/secretion of bile and controls the tendons/sinews. The health of the liver can also be seen in the nails and in the eyes. The associated emotion with the liver is anger.
The spleen, located in the middle energizer, controls the blood that the heart distributes and that the liver stores. Most importantly, it is the main organ for the manufacture of qi and blood and governs over the transportation (digestion) and transformation (transmission) of nutrient substance. The health of the spleen can be seen in the muscles, four limbs, mouth, and lips. The emotion that is said to affect the spleen the most is thinking or pensiveness.
The lung controls respiration and dominates qi of respiration and qi of the whole body. It also distributes defensive qi and body fluid to the skin, hair, and muscles, while the skin disperses the qi and defends the body from external pathogens. Also, the lung descends and regulates water passageways for smooth circulation and excretion of water in tandem with the kidney and bladder. The lung is associated with the emotion of sadness or grief. Lastly, the lungs open up into the nose and throat as gateways of respiration.
The kidney helps the lung in receiving and descending qi, stores congenital and acquired essence, dominates development and reproduction, and contains the foundations for yin (kidney yin) and yang (kidney yang) in the body. Furthermore, kidney qi regulates the distribution of body fluid and sends clear fluid to the lung for circulation while turbid fluid goes to the bladder. The health of the kidneys can be seen in the bones and hair, and is connected to the ear and anterior/posterior orifices of the human body. Fear is the emotion that is said to affect the kidneys the most.
The gallbladder aids in digestion, helps descend qi, and helps to maintain the free flow of qi with its partner organ, the liver. The stomach is also important in digestion because it receives and decomposes food. Together with the spleen, the stomach creates acquired foundation for the body and helps in descending qi. After the stomach, the small intestine receives, digests, and separates the clear from the turbid. The large intestine then receives the waste material, absorbs fluid content, forms feces, and then excretes it with the help of lung qi. If the large intestine eliminates solid waste, the bladder temporarily stores urine and relies on qi activity to discharge it. It works hand-in-hand with the kidneys, wherein kidney qi assists it in opening and closing to metabolise body fluid. Lastly, the san jiao or triple energizer functions as the governor of the different forms of qi and facilitates the circulation of quanqi and body fluid from the kidney to the different zang-fu organs. Each energizer functions in relation to the organs that it is located in front of: the upper energizer above the diaphragm dominates essential qi to the heart and lung, the middle energizer dominates digestion, and the lower energizer facilitates the separation of turbid/clear and the discharge of wastes from the body.