Functions of the Liver
The Liver is referred to as the body's general in the Simple Questions. The liver plans and oversees the direction and efficiency of the flow of qi. It in turn influences the degree of determination and resolve, and the ability to make decisions in life. It is internally-externally related to the Gallbladder. Its element is Wood.
Stores the Blood
The liver controls the flow of blood out into the muscles and sinews during activity, as well as the return of the blood back into itself during rest. Proper nourishment of the muscles is necessary to ensure enough energy to be active, and thus how well the liver does its job greatly effects the level of energy in the body. As a side effect of this, the quantity of blood available to ensure the nourishment of the muscles and surface help promote the strength of the Wei Qi (Defensive Qi).
Menstruation is also greatly effected by this function of the liver. The volume stored in the liver determines the flow of the menses. Deficient liver blood will lead to a scanty flow or amenorrhea (lack of period). Excess liver blood will lead to heavy flows, extended periods, or even spotting mid-cycle. Stagnation of liver qi may lead to stagnant liver blood and thus cause dysmenorrhea (painful periods), clotting in the flow and PMS. Finally, since the liver is where the blood is stored and nourished, a liver in disharmony (from qi stagnation, dampness, heat, etc.) may affect the blood. It may become reckless or hot and cause skin problems or emotional problems.
Maintains the Smooth Flow of Qi
Each individual organ usually has a direction in which its qi flows (e.g. the stomach descends while the spleen rises). The liver qi goes in all directions and ensures that the other organs go the way they are supposed to. This prime aspect of the liver can have great affect on three aspects of the body: the emotions, digestion, and free flow of blood.
1) Aside from the heart, the liver is closely related to the emotions. A lack of smooth flow of the liver qi will not allow the mind to be at ease. If it is stagnant it will cause depression, sadness, oppression of the chest or plum pit throat (a lump in the throat). If it is hyperactive it will cause restlessness, insomnia, dizziness and vertigo.
2) The liver assists in the smooth flow of the stomach and spleen qi, especially. If the liver qi is not flowing smoothly, bile will not be introduced properly and the liver will attack the stomach and spleen. This can result in nausea, vomiting, belching, reflux, chest and hypochondriac pain, even diarrhea.
3) The blood cannot go where the qi does not. In the vessels the qi and blood move together. If the free flow of the qi is stagnated by the liver, the blood will in turn stagnate as well. Though the heart and lung are the promoters of blood circulation, stagnation of liver qi will still cause stagnation of blood which will lead to the GYN symptoms above, as well as the formation of masses and hypochondric pain.
Controls the Tendons & Sinews
The tendons are the main tissues linking the joints and muscles, and dominate the movement of the limbs. The liver nourishes the tendons of the whole body to maintain their normal physiological activities. Thus, when liver blood is deficient, it may deprive the tendons of nourishment and give rise to weakness of the tendons, numbness of the limbs, and dysfunction of the joints. When the tendons are invaded by the pathogenic heat of the liver caused by liver yang rising or by chronic liver qi stagnation, there may be convulsions of the four extremities, opisthotonos and clenching of the teeth.
Opens Into the Eyes
The free movement of the blood from the liver gives the eyes their brightness and shine. When liver blood is abundant the vision is clear and crisp. When it is deficient, the vision is blurred, dry and conditions such as myopia can develop. If the liver fire or yang is rising, heat can get into the eyes and cause them to be red, dry, irritated. If the fire is strong enough to become wind, it may cause the eyes to turn upwards or to move involuntarily.
Manifests in the Nails
When liver blood is ample, the tendons and nails are strong, and when liver blood is deficient, the nails become soft and brittle.
Houses the Ethereal Soul (Hun)
As the Lungs house the physical or corporeal soul, it is the liver the houses the spiritual or ethereal soul. The ethereal soul is very similar to a western concept of the soul. It is that in the body which gives it both life and purpose. Without it we would lose direction and be empty. The ethereal soul is important to classical chinese medicine because it is the ethereal soul that leaves the body to join the spirits and qi of nature. When the popular thought that disease was caused by the curse of evil spirits and demons (sometime during the Chou period before ~220 BC), it was the ethereal soul of ancestors that were coming to haunt and plague the ill. The ethereal soul gives us guidance and a sense of purpose. When the liver blood is deficient it cannot root the ethereal soul and thus we lose direction in life. A sensation of fear or of floating prior to sleep can indicate this.