How the five Zang relate wǔ zàng xiāng guān lùn · 五脏相关论

The five Zang are not treated as independent units. Classical reasoning links them in two ways: through the generating and controlling relations of the five phases, and through direct physiological pairings such as Heart and Lung jointly governing qi and Blood, or Liver and Spleen jointly affecting digestion.

A practical consequence is that a complaint in one system is often discussed in terms of another. Irritable bowel-type presentations, for instance, are described as Liver overacting on the Spleen. This is why a TCM consultation so often ranges across symptoms that appear unrelated to the original complaint.