The liver is located below the diaphragm and in the right rib-side. The liver "pertains to yin in entity and yang in function"; This is the physiological characteristics of the liver. As one of the five zang-organs, the liver pertains to yin because it stores yin-blood. However in function the liver pertains to yang because yang-qi in the liver is very active and resolute, tending to disperse. That is why the liver is described as "a general-organ".
The physiological functions of the liver
The liver possesses two physiological functions: to govern shu-xie (dredging and regulating) and to store blood.
1. To dredge and regulate
Shu-xie in Chinese means to dredge and smooth the route of something. The liver governing shu-xie actually means that the liver dredges the routes and regulates the movement of qi so as to ensure smooth flow of qi in the body. The movement of qi is described as qi-ji (qi activity) in TCM. So to regulate the movement of qi means to regulate the activity of qi. The physiological activities of all the internal organs and tissues depend on the normal movement of qi. Since the liver can regulate the activity of qi, it plays an important role in regulating the physiological functions of all the internal organs and tissues. The function of the liver to regulate qi activity is demonstrated in the following aspects:
(1) To promote circulation of blood and metabolism of body fluid:
Blood circulation and body fluid metabolism all depend on the propelling function of the visceral qi, the normal flow of which relies on the regulating and dredging function of the liver which are prerequisite to constant blood circulation and normal metabolism of body fluid. If the movement of qi is abnormal due to failure of the liver to dredge and regulate, it may affect blood circulation and body fluid metabolism, bringing on corresponding pathologic changes. For example, if the liver is weak in dredging and regulating, the activity of qi will be stagnated and blood circulation will be otstructed, leading to blood stasis; or if the liver is hyperactive in dredging and regulating, blood will flow adversely with qi, causing haematemesis; or if qi activity is obstructed, water passage will be stagnated, leading to phlegm, rheum and edema.
(2) To assist the spleen and the stomach to digest food:
The digestion and absorption of food are accomplished by the spleen and the stomach. However, the dredging and regulating functions of the liver play an important role in the process of digestion. Because the liver regulates the activity of spleen-qi and stomach-qi with its dredging and regulating functions, ensuring a harmonious balance between the function of spleen-qi to elevate the lucid and the function of the stomach-qi to descend the turbid so as to guarantee a normal process of digestion. Besides, the bile, accumulation of surplus liver-qi, comes from the liver and excretes into the small intestine to assist digestion. The normal secretion and excretion of the bile are closely related to the dredging and regulating functions of the liver. If the dredging and regulating functions of the liver are abnormal, the activity of spleen-qi, stomach-qi and gallbladder-qi will be affected, leading to disturbance in digesting and absorbing food. If liver-qi attacks the spleen and the stomach, the activities of spleen-qi and stomach-qi will be affected, subsequently leading to abdominal distension, abdominal pain and diarrhea due to failure of spleen-qi to ascend on the one hand, and gastric distension and pain, vomiting and hiccup due to failure of stomach-qi to descend on the other. If failure of the liver to dredge and regulate affects the secretion and excretion of the bile, it will also bring on symptoms due to disharmony between the liver and gallbladder, such as hypochondriac pain, jaundice and anorexia.
(3) To regulate mental activity:
Mental activity refers to psychological activities such as joy, anger, anxiety and contemplation, etc. Mental activity, part of spiritual activity, is dominated by the heart and closely related to the dredging and regulating functions of the liver. The normal mental activity depends on sufficiency of blood and smooth activity of qi which can be promoted by the liver. With the normal functions of the heart and the liver, qi and blood will flow harmoniously and smoothly, making it better for people to regulate their mental activities and enjoy happiness and pleasure. If qi activity is in disorder due to failure of the liver to dredge and regulate, it will lead to abnormal changes of mental activities, such as heavy heart, melancholy, sentimentality, hiccup and sigh due to stagnation of liver-qi. If liver-qi flows adversely, qi will stagnate and transform into fire, bringing on symptoms of irascibility, susceptibility to rage, reddish complexion and eyes, head distension and headache due to hyperactivity of liver-qi.
(4) To regulate menstruation:
The physiological characteristics of women, such as menstruation, pregnancy and delivery, are closely related to blood. The liver regulates the activity of qi to enable blood to flow downward into the uterus to meet the need for menstruation, pregnancy and delivery. That is why it was said in ancient times that "the congenital base for women is the liver";. If the liver fails to dredge and regulate, it will clinically lead to various women diseases, such as irregular menstruation, dysmenorrhea, amenorrhea and sterility.
2. To store blood
The liver storing blood refers to the function of the liver to store blood and regulate the volume of blood.
The physiological significance of the liver to store blood lies in the fact that liver-blood nourishes the liver itself. With the nourishment of blood, the liver will have sufficient yin-fluid to prevent liver-yang from becoming hyperactive. Besides, in the course of regulating blood volume, liver-blood can nourish the tissues and organs in the whole body to sustain their physiological activities.
The liver storing blood is a course in which blood enters the liver and comes out of the liver. Under physiological condition, the volume of blood in different parts of the body varies due to the difference of their physiological activities. Generally speaking, the organs in the body comparatively need less blood when the body is in a quiet state, the rest of blood flows into the liver. When the body takes strenuous activities or when people become excited, the organs in the body comparatively need more blood. In this case, the liver transports blood stored to other parts of the body to meet the need of their physiological activities. If physiological activities are different, the volume of blood needed is also different. In fact the blood needed by different organs and tissues constantly varies with the change of physiological activities. Such a constant variation is also closely related to the function of the liver to store blood. That is to say that the liver, based on its function to store blood, adjusts the volume of blood to meet the need of different physiological activities.
If the function of the liver to store blood is in disorder, it may lead to two kinds of pathological changes. One is insufficiency of liver-blood. In this case the body cannot get enough nourishment, leading to dizziness, vertigo, weakness of limbs, scanty and light-colored menses or amenorrhea. The other is failure of the liver to store blood which may lead to abnormal flow of blood, causing various symptoms such as haematemesis, epistaxis, hematochezia and profuse menorrhea, or even constant haematemesis or sudden profuse uterine bleeding in severe cases.
The relationships between the liver and the body, the sensory organs and the orifices
1. The liver governing the tendons
The tendons are the tissues that connect the muscles, the skeleton and the joints. The contraction and relaxation of the tendons maintain the flexion and extension or lateral rotation of the joints.
The liver governing the tendons means that the physiological functions of the tendons depend on liver-blood to nourish and liver-yin to moisten. Only when liver-yin and liver-blood are sufficient can the tendons get enough nourishment and the joints move flexibly and powerfully. If liver-yin and liver-blood are deficient, the tendons cannot get enough nourishment, leading to unsmooth movement of the joints, tremor of hands and feet, numbness of the limbs or susceptibility to fatigue.
2. The liver opening into the eyes
The liver meridian runs upward into the eyes, So the eyes are nourished by liver-yin and liver-blood. Besides, the liver can regulate the activities of the eyes with its dredging and regulating functions. Thus eyesight is closely related to the liver. The conditions of the liver can be observed from the manifestations of the eyes. That is why it is said that "the liver opens into the eyes". For example, insufficiency of liver-yin and liver-blood may lead to dryness of the eyes and blurred vision; failure of the liver to dredge and regulate may lead to up-flaming of liver-fire, consequently bringing on redness, swelling and pain of the eyes and cataract.
Besides, the essence of the five zang-organs and six fu-organs all flows into the eyes. So the eyes are not only related to the liver, but also to the other viscera. For example, the white part of the eyes pertains to the lung that governs qi, so it is termed qi-wheel; the black part of the eyes pertains to the liver that governs wind, so it is termed wind-wheel; the internal and external canthi pertain to the heart that governs blood, so they are termed blood-wheel; the upper and lower eyelids pertain to the spleen, so they are termed muscle-wheels; the pupil pertains to the kidney that governs water, so it is termed water-wheel. Altogether they are called "five wheels".
3. The external manitestation of the liver on the nails
The nails here include both the nails of fingers and toes. TCM believes that the nails are the extensions of the tendons. The nails, like the tendons, depend on liver-blood to nourish. Thus deficiency of liver-blood often affects the color and quality of the nails. For example, if liver-blood is sufficient, the nails are firm and bright, ruddy and lustrous; if liver-blood is insufficient, the nails are soft and thin, or even deformed or brittle.