In TCM, Blood is a very dense and material form of Qi.
Blood is inseparable from Qi: Qi activates Blood, it gives it its life. Without it, Blood would be an inert fluid.
Blood is considered a Yin substance, as it is dense and fluid.
Blood originates from two sources: Grain Qi created from food and drinks, and bone marrow formed from Essence.
The process for the creation of Grain Qi is as follows: the Stomach first receives and 'ripens' food, and then the Spleen transforms it into a very refined substance, Grain Qi or Food Qi ("Gu Qi" in Chinese). To make it Blood, Spleen Qi then transports the Grain Qi up to the Lungs where it mixes with the Clean Air which they filtered from the air we breath. Lung Qi then propels this mixture of Grain Qi and Clean Air to the Heart where the transformation into Blood is completed.
In that last part of the process, Original Qi (Pre-Heaven Essence in its Qi form) plays a crucial role in helping the Heart produce Blood. And since Original Qi is stored in the Kidneys, their health is also important in the creation of Blood.
We can therefore say that Blood is generated by the interaction of Grain Qi from the Stomach and Spleen and Essence from the Kidneys (because it helps the Heart transform Grain Qi into Blood and because it helps generate bone marrow). This is why, to nourish Blood, Chinese Medicine often aims to tonify the Spleen and Kidneys.
This also means that the nutritional value of the diet, the basis for a healthy Grain Qi, directly influence the formation of Blood. This is one of the reasons why proper dieting is so important in Chinese Medicine.
The main function of Blood is to nourish the body. It circulates continuously within the vessels, traveling to the Organs in the Interior, and to the muscles, tendons, bones and skin in the Exterior, providing nutrients.
Blood also has the function of moistening the body, which Qi doesn't have. The Blood of various Organs ensures that the skin, hair, eyes, sinews and tongue are properly moistened. For example, Liver Blood moistens eyes and sinews (since the Liver "controls the sinews" and "opens into the eyes"), so that the eyes can see properly and the sinews are flexible and healthy.
Chinese Medicine believe that the Mind (Shen) lives in the Heart and more specifically in the Blood Vessels (part of the system of the Heart). Blood is therefore intricately connected to the Mind since the former harbours and nourishes the latter.
When Blood is Deficient, the Mind lacks its foundation, resulting in restlessness, anxiety, slight irritability, a feeling of dissatisfaction and insomnia.
Pathologies of the Blood in women often primarily manifest themselves via their impact on menstruation. For instance Blood Deficiency leads to scanty periods or an absence of period. Similarly Blood Heat often causes heavy periods.
The circulation of Blood results from the mutual action of the Heart, Lungs, Spleen, Liver and Kidneys. The Heart governs the Blood by making it circulate, the Spleen makes the Blood by creating Grain Qi, the Liver stores the Blood, Lung Qi enters the Heart to promote the transformation of Blood and the Kidneys also have a strong role in the Blood creation process.
For example, a Deficiency of Heart Qi and Lung Qi may lead to Stagnation of Blood of the Heart; a Deficiency of Spleen Qi may lead to various bleedings; irregular Liver Qi may cause Blood Stagnation; and a Deficiency of Kidney Essence can lead to a Deficiency of Blood. Of all these, the Heart, Spleen and Liver are the most important relationships with Blood.
The Heart governs Blood. It is the place where Heart Fire (Yang) transforms the mixture of Grain Qi and Clean Air into Blood (Yin). It also is responsible for the circulation of Blood throughout the body to all the Organs, muscles, tendons, sinews, skin and hair.
The Spleen is the origin of Blood, as it produces Grain Qi which transforms into Blood. Spleen Qi is responsible for keeping Blood in the vessels so that it does not extravasate. If Spleen Qi is Deficient, Qi cannot hold Blood in the vessels and that may result in various forms of bleedings as well as a tendency to easily bruise oneself.
The Liver stores Blood. This important function has several meanings. When a person is active, Blood flows to the muscles and sinews to moisten them for flexibility and movement. When a person rests, Blood moves back to the Liver where it is stored and regenerated. Therefore it is important to rest and lie down when there is a Blood Deficiency (especially Liver Blood Deficiency).
Liver Blood also functions to moisten the eyes, promoting good eyesight, and the sinews and tendons, supplying flexibility to the joints.
Thirdly the Liver also smoothes and regulates the flow of Qi and Blood. Thus, it regulates the rate of Blood flow within the vessels according to our different physiological needs (activity, rest, etc.).
Lastly Liver Blood supplies the Uterus with Blood and is extremely important for the physiology and pathology of menstruation. Because the Liver also regulates the rate of Blood flow, periods which are too light or heavy are often due to a disharmony of the Liver Blood. Deficient Liver Blood can lead to amenorrhea or scanty periods, while Stagnant Liver Blood can cause painful periods.
A traditional saying states that "Qi is the commander of the Blood. Blood is the mother of Qi." This refers to the inseparable relationship between Blood and Qi. Blood is actually a form of Qi, albeit a very dense one.
The close relationship between Blood and Qi can be observed when patients suffer from a massive loss of Blood: the person develops signs of Qi Deficiency, such as sweating, breathlessness and cold limbs. The same is true when one suffers from a loss of Qi (after, for instance, prolonged and heavy sweating that depletes Qi): one may develop signs of Blood Deficiency, such as pallor, numbness, dizziness and palpitations.
Grain Qi from food is the foundation of Blood; combined with Clean Air from Lung Qi, it is essential for Blood production. Thus if Qi is Deficient, Blood will also eventually become Deficient. This is why Qi tonics are frequently given with Blood tonics as a remedy for a Deficiency of Blood.
Qi is the force which moves and circulates Blood. If Qi is Deficient or doesn't move sufficiently, it can't then push the Blood and Blood Stagnates. A traditional Chinese Medicine goes "When Qi moves, Blood follows" and "If Qi Stagnates, Blood congeals".
Qi is in charge of holding Blood in the vessels, if it is Deficient, Blood may move out of its pathways, resulting in various forms of bleedings.
This function belongs primarily to the Spleen. If Spleen Qi is Deficient, Qi cannot hold Blood, and there may be bleedings. However, Kidney Qi also plays an important role in keeping Blood in the Uterus vessels.
Blood nourishes the Organs that produce and regulate Qi. It also provides a material foundation for Qi which prevents it from rising up or 'floating', causing symptoms of Empty Heat.
As we've seen in the section on the origin of Blood above, Essence stored in the Kidneys plays a critical role in the formation of Blood. However it's a mutually beneficial relationship because Blood also nourishes and replenishes the so-called "Post-Heaven Essence".
In Blood Deficiency, there is insufficient Blood to nourish and moisten the body. This usually affects the Organs with which it has special relationships. This is mostly caused by a Deficiency of Spleen Qi and Stomach Qi since those are the two Organs most involved in the creation of Blood. However, other Organs may also be implicated, in particular the Liver and Kidneys.
In Blood Heat, too much Heat in the body, usually in the Liver (since it stored Blood), causes Heat in the Blood and pushes it out of the vessels. In women, Blood Heat often causes heavy periods. Many skin diseases are also due to Blood Heat.