In Chinese medicine, Blood is the substance that is continually circulating through the body and nourishing it. Blood disharmonies are a major feature of Chinese understanding of health, disease and medical treatment. There are two major patterns of disharmony associated with disharmonies of Blood: deficient Blood (when the body or particular Organs are insufficiently nourished by Blood) and congealed Blood (when flow of the Blood is obstructed).
Just as the Earth is comprised of land, ocean and atmosphere, so the body is organized as Blood, Moisture and Qi. Qi governs the shape and activity of the body and its process of forming and organizing itself. Blood governs tissue, the material form of the body. Moisture governs the internal environment, the body's inner ocean. Without Blood, Moisture is dispersed and Qi is scattered.
Moisture and Blood are both Yin in quality and sometimes talked about together, under the name Blood. Moisture is the intermediate state of Blood generating to Qi and Qi transforming Blood. Blood is often called the "mother of Qi". Qi and Blood are intimately related in a feedback loop where Blood nourishes the Organs that produce and regulate the Qi, and Qi creates and moves the Blood, together with Shen.