The kidney is the ocean of the human body. Since oceans are situated on a lower level than the earth's streams and rivers, they draw every one of them to form one large body of water. Oceans may appear vast and inexhaustible, yet they still drain off some of their seemingly unlimited supply. One way of drainage is called 'going to ruins,' meaning the water drains down into the earth from where it will not return. The other way of drainage is called 'dwelling with the stars,' meaning the water steams toward the sky and later rains down to earth again, where it dissipates into rivers and streams and eventually returns to the ocean. This is the water that circulates between heaven and earth, always striving to keep an equilibrium between the extreme states of drought and flooding.
In the context of the human body only the kidney can be compared to the workings of this natural cycle. All the essences and fluids of the body's various pathways pour into the kidney. After the kidney has assembled the essential fluids of the body's vessels, it also experiences two ways of drainage: one way is through the sexual urge which draws the essence downward to the sexual centers; once it exits from here it cannot come back into the system, so this is just like the ocean "going to ruins." The other way is the upward dispersal by way of the suctioning affect of true qi, which draws the body's combined essences all the way up to the flower pond (mouth); from here it moves down through the throat into the stomach, lubricating the five organ networks, nourishing all of the body's pathways, and finally returning to the kidney. This is the microcosmic process of ascending and descending that can be compared to the ocean 'dwelling with the stars.'