The five zang-organs include the heart, the lung, the liver, the spleen and the kidney.
The five constituents include the vessels, the skin, the tendons, the muscles and the bones that are dominated by the five zang-organs respectively.
The heart is located in the chest between the two lobes of the lung. The heart occupies the first place among the five zang-organs and governs the life activities of the whole body. That is why it is said that the heart is "an organ of monarch" in Huangdi Neijing.
The physiological functions of the heart
The physiological functions of the heart are mainly to govern blood and to control the mind.
1. Governing blood
The function of the heart to govern blood means that the heart propels blood to circulate in the vessels and that the heart is related to the production of blood.
Blood circulates inside the vessels. Since the heart is connected directly with the vessels, its beat is the motive power to propel blood to flow in the vessels. Thus a relatively independent blood circulation system is formed with the heart, the vessels and blood. Only under the propelling of the heart beat and the control of the vessels can blood normally circulate all through the body, in which the heart beat is key to blood circulation.
The reason that the heart propels blood to circulate within the vessels lies in the propelling and warming functions of heart-qi and heart-yang as well as the nourishing and moistening functions of heart-yin and heart-blood. Sufficiency of heart-qi, heart blood, heart-yin and heart-yang guarantee normal beat of the heart and continuous circulation of blood to nourish all parts of the body, thus maintaining the normal physiological functions of all tissues and organs with the manifestations of full vitality, ruddy complexion and normal pulse. However, if heart-qi, heart-blood, heart-yin and heart-yang are insufficient or in disturbance, the function of the heart to govern the vessels with be affected, leading to a series of pathological changes such as pale complexion and thin and weak pulse due to insufficiency of heart-qi as well as cyanotic complexion and unsmooth pulse or slow pulse with irregular intervals or slow regular intermittent pulse due to stagnation of heart-blood.
The heart also plays a role in the production of blood, known as "reddening"; in TCM. After digestion and absorption of food by the spleen and stomach, the refined nutrients are transported up to the heart and the lung. Combined with the fresh air inhaled into the lung, warmed and steamed by heart-yang, these refined nutrients are transformed into red blood.
Besides, TCM believes that "the heart controls blood vessels , acombination of the ideas that "the heart governs blood" and "the heart controls the vessels". The idea that "the heart controls blood and vessels" is described in the section of "the relationship between the heart and the body, the sensory organs and the orifices.";
2. Controlling the mind
The function of the heart to control the mind is also known as "the heart storing spirit". In a broad sense, spirit refers to the supreme dominator of life activities in the whole body. In a narrow sense, spirit is a collective term for cognition, thinking, consciousness and mental states. The idea that the heart controls the mind means that the heart governs the mental activities.
The mental activities are closely related to the response of the brain to the external environment and certain intrinsic functions of the brain. Centering around the five zang-organs, TCM attributes the motivation of mental activities to the heart. It is obviously that the conception of the heart in TCM includes certain functions of the brain.
The normal function of the heart to control the mind depends on the nourishing and moistening functions of heart-blood and heart-yin which are the essential substantial bases for mental activities. Heart-qi and heart-yang function to activate and stimulate heart-spirit, which also plays an important role in ensuring the normal function of the heart to control the mind. If the function of the heart to control the mind is normal, people will be full of vigor, conscious in mind, agile in thinking and keen in response. If the function of the heart to control the mind is abnormal due to insufficiency or disturbance of heart-qi, heart-blood, heart-yin and heart-yang, it will inevitably lead to palpitation, insomnia, dreaminess, or even coma, delirium and unconsciousness.
The relationships between the heart and the body, the sensory organs and the orifices
1. The heart governs the vessels
The vessels are the routes for blood circulation. Normal function of the heart and smoothness of the vessels guarantee the normal flow of blood and the normal state of the pulse. However, abnormal function of the heart or unsmoothness of the vessels will disturb blood circulation and affect the state of the pulse. For example, insufficiency of heart-blood and emptiness of blood vessels will lead to thin and weak pulse; insufficiency of heart-yang will bring on deep and indistinct pulse.
2. The heart opens into the tongue
The idea that the heart opens into the tongue indicates that there is a special relationship between the heart and the tongue. For example, the state of the tongue can reflect the physiological functions and pathological changes of the heart because a branch of the heart meridian runs into the tongue. So the condition of heart-blood displays itself on the tongue. On the other hand, heart-spirit directly influences the sensation and the movement of the tongue. Thus whether the heart functions well in governing the vessels or in controlling the mind can be understood from the color and shape of the tongue. That is why it is said that "the tongue is the sprout of the heart" in TCM. If heart-qi, heart-blood, heart-yin and heart-yang are normal, the tongue is ruddy and lustrous in appearance, agile in movement, soft in texture, keen in taste and fluent in speaking. So insufficiency of heart-blood leads to lightly whitish tongue without taste; up-flaming of heart-fire brings on deep colored tongue or ulcerated tongue; abnormal heart-spirit results in curled tongue, stiff tongue and dysphasia.
3. External manifestation on the face
Since the condition of heart-qi, heart-blood, heart-yin and heart-yang mainly display on the face, observation of facial color and shape can enable one to know whether heart-qi, heart-blood, heart-yin and heart-yang are normal or not. If heart-blood is sufficient and flows smoothly, face is ruddy and lustrous; if heart-qi is insufficient and heart-blood is deficient, the face is pale and lusterless; if heart-blood is stagnated, the face is cyanotic.
Appendix: The pericardium
The pericardium is a tissue surrounding the heart to protect the heart. Zangxiang theory holds that the heart is the monarch-organ and cannot be directly attacked by pathogenic factors. If pathogenic factors directly invade the heart, it will disturb heart-spirit and threaten life. So when pathogenic factors invade the heart, they first attack the pericardium. For example, the symptoms of high fever, coma and delirium in exogenous febrile diseases are described as "invasion of pathogenic factors into the pericardium" in TCM.