No organ carries more weight in Chinese medicine than the Kidney, and the difference from the western anatomical organ is correspondingly large. The Kidney is one of the five zang, belongs to the Water phase, pairs with the Bladder, and is assigned winter, fear, the ears as its orifice, the bones and marrow as its tissue, and the north.
Beyond those regular correspondences it is given a role nothing else has. The tradition describes it as storing jing, the essence: the constitutional endowment received at conception, held to be finite and gradually spent, from which growth, maturation, reproduction and ageing all proceed. The Inner Canon's account of the human life course in cycles of seven years for women and eight for men is written entirely in those terms. Later writers call the Kidney the root of the prenatal, as against the Spleen and Stomach which make the postnatal from food.
Because of this the Kidney is described as containing both the deepest yin and the source of yang for the whole body, which is unusual in a system that otherwise keeps the two carefully apart.
This is the tradition's own model and the atlas reports it as such. The Chinese Kidney is not the anatomical kidney, no claim about renal function is being made, and nothing here is medical guidance.