In the modern Western medical science, a liver belongs to the digestive system. It is the largest digestive gland and the vital organ of biological metabolism. The liver can store abundant blood for keeping normal blood circulation and excrete bile for promoting digestion. In the traditional Chinese medical science, some functions of a liver are the same as the liver in the modern Western medical science, but more functions are different.
Between traditional medical science and modern medical science, the similar function of a liver is to store blood. The theory of the traditional Chinese medical science says that, when a person is quiet or sleeping, much blood is stored in the liver. When a person is doing sports, the stored blood will be released to the blood circulation. The significance of storing blood is not only this. The stored blood can nourish the liver and the organs which are related to the liver. The eyes, tendons, ligaments, fingernails and toenails are related to the liver, and all of them are nourished by the blood which is stored in the liver. The book “Su Wen” (素问), one of famous traditional medical classics, says, “The liver receives blood, so eyes can see. Feet receive blood, so they can walk. A palm receives blood, so it can hold. Fingers receive blood, so they can grasp.” Moreover, blood is deemed to the physical base of mental actions. When the blood of the liver is ample, the person has a balanced mind. But if the blood of the liver is deficient, the person will feel timid, and suffer from dreamful sleep and insomnia, or even have somniloquy and hallucination.
The active substance of a liver is called “liver-Qi” (肝气). The liver-Qi has two important functions.
The first function of the liver-Qi is to unblock and smooth many important physiological processes of a body. Two kinds of physiological processes can be influenced by the liver-Qi.
The first kind is the circulation of Qi (气, the motivity of physiological functions of a body), blood and other bodily fluid (津液). If the liver-Qi is blocked, the circulation of Qi, blood and other bodily fluid will be sluggish. The stasis of Qi causes the distending and oppressing pain of chest and abdomen; the stasis of blood causes a woman to suffer from sluggish catamenia, dysmenorrhea and even amenorrhoea; the stasis of other bodily fluid can be transformed into pathological fluid, and even cause ascites. If the liver-Qi is pathologically sthenic, the liver-Qi will be ascending excessively and impact the head, so the head will suffer from distending and oppressing pain, and the eyes will be bloodshot and suffer from distending pain. The serious symptom is haematemesis, and even the person suddenly loses consciousness.
The second kind is digestive processes. The digestive processes are mainly related to the spleen and the stomach. The spleen-Qi (脾气, the active substance of the spleen) transmits nutrient substances and water upwards, and the stomach-Qi (胃气, the active substance of the stomach) transmits undigested residues downwards. The functioning of the spleen-Qi and the stomach-Qi is influenced by the liver-Qi. If the functioning of liver-Qi is abnormal, many nutrient substances can’t be transmitted upwards by the spleen-Qi, and then the person will feel faint and have loose bowels; the undigested residues can’t be transmitted downwards well by the stomach-Qi, the person will suffer from vomit, bellyache and constipation. The digestion of food is promoted by bile. The bile originates from the liver-Qi and is stored in the gallbladder. The stagnancy of the liver-Qi can cause the stasis of bile, and the person will feel bitter taste and suffer from the distending and oppressing pain of the hepatobiliary area, dyspepsia and even jaundice.
The second function of the liver-Qi is to temper emotions. This function originates from the the function that the liver-Qi smoothes the circulation of Qi. The stasis of the liver-Qi can cause mental depression. If the liver-Qi is pathologically sthenic and ascending excessively, the person will be often enraged. So the anger is called the emotion of the liver. The furious anger also can cause the liver-Qi to ascend excessively, and even cause haematemesis.
In the traditional Chinese medical science, the eyes and tears are deemed to be related to the liver. The blood of the liver nourishes the eyes. With the unblocking and smoothing functions of the liver-Qi, eyes can function normally. So the medical classic “Ling Shu” (灵枢) says, “The liver-Qi connects with the eyes. So the liver works well, the eyes can distinguish colors correctly.” If the blood of the liver is deficient, the eyes will be dry and dim-sighted, and even the person will suffer from nyctalopia. If the liver-Yang (肝阳) or even the liver-fire (肝火) (Here “liver-Yang” and its more serious status “liver-fire” describe heated pathological conditions of the liver, which are similar to excitability and irritability but not general pyrexia) is scorching, the eyes will be bloodshot and suffer from hot, dry and pruritic pain, and even the person will feel vertiginous. If the liver-wind (肝风) (Here “Wind” describes a pathogeny which can cause numb, shaking or spastic symptoms) is violent, the eyes will be staring upwards or sideways, and the person may suffer from convulsions, epilepsy or even apoplexy. Because of the connection between the liver and the eyes, in the traditional Chinese medical science, ocular diseases are often attributed to the abnormal statuses of the liver, so giving treatment to the liver is often effective for curing ocular diseases. Eating the livers of animals is also helpful to improve the vision of a person.
Tendons and nails are also related to the liver. Nails are deemed to be the elongations of tendons. Both of tendons and nails are nourished by the liver-Qi and the blood which is stored in the liver. If the liver-Qi and the blood of the liver are deficient, tendons and nails can’t get enough nourishment, and the person will suffer from hypokinetic, shaking, benumbed or spastic symptoms. Being senile, the liver-Qi and the blood of the liver are gradually deficient, so motor activity is also decreased. The book “Su Wen” says, “If a man is 56 years old, his liver-Qi is deficient, and his tendons can’t work well.” The deficiency of the liver’s blood also causes nails to lose luster and rigidity. So the change of the luster and rigidity of nails can reflect the pathological status of the liver.