Kidney and Bladder: Water Storage, Fluids, and the Entry-Exit of Qi Transformation
Kidney
Section titled “Kidney”The North gives rise to Cold; Cold gives rise to Water; Water gives rise to saltiness; saltiness gives rise to the Kidney. The Kidney is “the official of strength, from which skill and capability emerge.” All bones belong to the Kidney, and it stores the will. Its trigram is Kan; in the body it corresponds to bone; its color is black; its voice is groaning; its emotion is fear; its movement-change is trembling; its orifices are the two lower Yin openings; its flavor is salty. Its fluid is spittle, its odor putrid, its external luster the hair of the head, its number six, its grain beans, its domestic animal pig, its creature the scaled class, its fruit chestnut, and its vegetable bean leaf. The Kidney is paired with the Bladder and is controlled by the Spleen. It dislikes Dryness; prolonged sitting on damp ground and excessive sexual exertion are said to injure it. Kidney disease may cause abdominal enlargement, swelling of the shins, panting and cough, heaviness of the body, night sweating, and aversion to Wind. In deficiency there may be chest pain, pain in the upper and lower abdomen, cold counterflow, and loss of emotional ease.
Bladder
Section titled “Bladder”The Bladder is “the official of the regional capital; fluids are stored there, and when qi-transformation occurs they can emerge.” Because it is paired with the Kidney, it is the fu of Cold-Water; because it can transform qi, it is also counted among the transmitting-and-transforming fu.
Traditional explanations say that water taken into the body ultimately reaches the Bladder. The Bladder is compared to sandbanks and collecting regions along rivers, hence the image of a regional capital. People commonly know only that the Bladder governs urination, but this passage emphasizes another direction of transformation: water entering the Bladder is transformed into qi; what rises becomes body fluids, while the residual material descends as urine. Thus “qi-transformation enables emergence” is interpreted here as the distribution of fluids, not merely the voiding of urine.
When Fire meets Water, qi is produced. The Heart governs Fire, while inhaled heavenly Yang is also treated as belonging to Fire. Inhaled heavenly Yang joins Heart Fire and descends to the lower abdominal reproductive region, steaming the Bladder’s Water and transforming it into qi. This qi passes out from the Bladder into the surrounding network, ascends along the qi-streets beside the navel, crosses the diaphragm to the Lung, and returns to the mouth and nose. Within the mouth, tongue, and zang-fu it becomes fluids; when it spreads outward through the skin and body hair to warm and moisten the flesh, it becomes sweat. This is the meaning of qi-transformation by which fluids can emerge.
The passage further relates inhalation and exhalation to the Du, Chong, and Ren vessels and to the interchange of Fire and Water. If Fire is insufficient to steam Water, fluids fail to rise and qi fails to transform; this is used to explain why Cinnamon Twig appears in Zhang Zhongjing’s Five-Ingredient Powder with Poria (Wu Ling San). If Water is insufficient to assist Fire, fluids dry up and urination becomes difficult; this is used to explain the use of Donkey-Hide Gelatin in Polyporus Decoction (Zhu Ling Tang).
A classical passage states that Bladder disease may cause unilateral swelling and pain of the lower abdomen; pressure with the hand creates an urge to urinate, yet urination cannot occur.