Traditional Chinese medicine (TCM) thinks that the organic human body is a constituted complex unity, taking the five internal organs as the core with the six hollow organs as the coordinate, meridian as mesh connecting the tissue and the organs, which forms five main systems. This is one part of systematic theory of TCM. Therefore, the relation among the five organs and the promotion between the five elements shouldn’t be missed out before talking about health preservation by TCM.
wood → fire → earth → metal → water

liver → heart → spleen → lung → kidney

    The wood promotes the fire means that wood of liver benefits the fire of the heart. If the normal function of the liver to store blood helps the heart to function as blood circulation controller. The fire promotes the earth refers to that the fire of the heart warms the earth of the spleen. Only when the heart is working normally to control blood circulation and the blood nourishes the spleen, then the spleen functions well to direct digestion and transportation of the nourishment, to develop blood and manage the blood. The earth promotes the metal means the earth of the spleen supports the lung metal. The spleen benefits the qi (vital energy), which promotes blood production. Then it transfers essence of nutrition to the lung, so that the lung would make the qi clean and smooth. The metal of lung fosters the water of the kidney. The purified and descended qi of lung contributes to kidneys’ function of storage of essence, qi and water supply. The water of the kidney nourishes the wood of the liver. The essence stored by kidney could be transferred to liver blood, so as to support the liver’s good function. This is the promoting relation among the five internal organs illustrated by the promotion theory of the five elements. 

    Now, let’s see the restraint relationship of the five internal organs. The water of kidney restricts the fire of the heart. The fire more than enough of the heart could be prevented when the water of the hear rises up to reach the heart. The fire of the heart restricts the metal of the lung. The heat of the fire prevents the over purifying and descending. The metal of the lung restricts the wood of the liver. The over degree of purifying and descending inhibits the rising of yang of the liver. The wood of the liver restricts the earth of the earth. The smoothness of the liver can do catharsis for the congestion of the spleen pneuma. The earth of the spleen restricts the water of the kidney. The function of transportation and transformation of the spleen prevents overflow of the water.