The Kidney holds a position in Chinese medicine that no single organ holds in the biomedical scheme. It is described as the store of jing, usually translated essence: the inherited constitutional endowment a person is born with, which the tradition holds to be finite, gradually spent, and not fully replaceable. Growth, maturation, reproduction and ageing are all attributed to its state, and the Inner Canon's famous account of human development in cycles of seven years for women and eight for men is written entirely in terms of Kidney essence waxing and waning.
That makes the Kidney the deepest yin of the system, and the channel is drawn accordingly, rising from the sole of the foot, the lowest point on the body, up the inner leg to the chest. Its first point, Yongquan, Kidney 1, is the only point on the sole, and the tradition describes it as the place where the body touches the earth.
The Kidney is also paired in the classical literature with fear as its associated emotion, and with the Water phase, winter, and the north.
Everything above is what the tradition holds. The Chinese Kidney is not the anatomical kidney and the atlas makes no claim about renal function, about ageing, or about fertility. Nothing here is clinical guidance and nothing here should displace a clinician.