These systems are named after specific organs, though the systems and organs are not directly associated. The zang systems are associated with the solid yin organs, such as the liver, while the fu systems are associated with the hollow yang organs, such as the intestines.
Yinyang health is explained as a state of balance between the yin and yang, with disease ascribed to either of these forces being unbalanced, blocked, or stagnant. The yang force is the immaterial qi, a concept that is roughly translated as vital energy.
The yin counterpart is blood, which is linked to but not identical with physical blood, and capitalized to distinguish the 2. TCM uses a variety of interventions, including pressure, heat, and acupuncture, and applied to the body's acupuncture points.