Traditional Chinese Medicine (TCM) believes that the liver can "store blood," which has two implications:

• Storing blood: Neijing-Wuzang Shengcheng states, "When a person lies down, blood returns to the liver," meaning that when a person sleeps, bodily activity decreases, and the need for blood supply reduces. Therefore, some blood is stored in the liver. Modern medicine has discovered that the liver is the largest blood reservoir in the human body, with its usual blood volume accounting for about 14% of the total blood volume. The blood vessels in the liver are controlled by the sympathetic nervous system, which can regulate the blood volume in the liver. In TCM, the sympathetic nervous system is also considered part of "liver qi" (to be discussed later). The spleen is the second small blood reservoir in the human body. When the body is short of blood, the spleen can also squeeze out some, providing a small supplement. Therefore, "liver storing blood" also includes some functions of the spleen.
• Storing reserve substances: Neijing-Liujie Zangxiang Lun states, "The liver is the foundation of exhaustion," meaning that when a person lacks food or has not eaten for a long time, the liver must release the various nutrients it usually stores for emergency use. Therefore, the liver is the last resort. Modern medicine has found that the liver stores a lot of glycogen, fat, vitamins, and minerals for emergency use by the body. If used sparingly, glycogen can provide energy for the body for about 18 hours.