Which organ is described as "filling up the brain" according to traditional beliefs?

In traditional Chinese medicine (TCM), the kidney is considered a vital organ that holds a deep connection to overall health and vitality. This belief stems from the understanding of the kidneys as the source of "Jing" or essence, which is thought to be foundational for various bodily functions, including development and reproduction. The kidneys are also believed to play a role in mental functions and consciousness.

The phrase "filling up the brain" reflects the idea that kidney health is closely tied to brain function. TCM proposes that the kidneys possess a nurturing effect on the brain through the nourishing essence they provide. A deficiency in kidney energy, or "Yin," can lead to mental fog, poor memory, and a lack of clarity, thus illustrating the intimate relationship between the kidneys and mental faculties.

In contrast, other organs like the heart, liver, and lungs serve different functions according to TCM principles. While the heart is associated with the mind and emotions, the liver is linked to the smooth flow of Qi and emotional balance, and the lungs are associated with the process of respiration and immunity. Understanding the unique roles of these organs helps clarify why the kidneys are specifically seen as "filling up the brain" in traditional beliefs.