In Chinese medicine Blood is a considered to be a red, fluid-like vital substance. I say “fluid-like” because while it does flow it is substantive and thick, and more like yin than like Qi.
The Source of Blood
The discussion of the ‘source of Blood’ can get confusing. Let me break it down for you. Bear in mind this is the ancient medicine understanding. I’ll tie modern medicine in momentarily.
You ingest stuff like apples, spinach, gluten-free politically correct donuts made from fair trade spelt flour, and herb tea. Your Stomach grinds it into a slurry called chyme and passes it to the Small Intestine.
The villi in the Small intestine gets coated with chyme where the nutrients are absorbed and the waste is passed to the Large Intestine. This, in TCM terms, is separating the clear or pure (the digestible usable nutrients) from the turbid (stuff your body can’t use). Much of this energy is provided by the Spleen and Stomach, the masters of the middle jiao.
Spleen creates Ying Qi from the pure stuff and ascends it up to the Lungs.
Lungs push the Ying Qi and body fluids to the Heart.
The Heart, using the Yuan Qi provided by the Kidneys, transforms the Ying Qi and body fluids into blood.
Western medicine says that blood comes from the marrow in the bones. True. About 200 years ago during the Qin Dynasty some scholars began to say that Blood was sourced from the Kidney essence, which is responsible for marrow. In Anatomy and Physiology studies you might remember that the kidneys produce erythropoietin which prompts the production of red blood cells. Without the Kidney there would be no red blood cell production. But without the other organs bolded above there would be no nourishment in the blood, nor would there be any energy to push it around.