In the theory of meridians, traditional herbal medicine posits that ancient practitioners, through long-term observation and reasoning, believed that the pericardium also functions as an organ with its own meridian system, alongside the corresponding meridian systems. Thus, there are six organs and six bowels, totaling twelve organs and twelve meridians.
The meridians are a collective term for the primary and collateral meridians. In the dynamic laws of the body’s circulation, ancient practitioners, through long-term observation and reasoning, believed that they serve as pathways for the circulation of qi and blood, connecting the organs and tissues, facilitating communication between the internal and external environments, and transmitting information. They are an essential component of the body’s structure and the dynamic laws of circulation, contributing to the self-regulating (yin-yang balance) functions. As stated in the “Lingshu” (Spiritual Pivot) chapter on the organs, “The meridians are responsible for the circulation of blood and qi, nourishing the tendons and bones, and facilitating the joints.” The “Lingshu” chapter on the sea states, “The twelve meridians are internally connected to the organs and externally linked to the limbs and joints.”
Meridians are divided into two main categories: primary meridians and collateral meridians. Ancient practitioners, through long-term observation and reasoning, believed that the primary meridians are straight pathways, serving as the main conduits of the meridian system, while collateral meridians branch off from the primary meridians, signifying connections and networks. For instance, Li Zhen in the “Introduction to Medicine” states, “The straight pathways are the primary meridians.” The “Lingshu” chapter on pulse measurement states, “The branches that are horizontal are the collaterals.” They intertwine and spread throughout the body, connecting the five organs, six bowels, limbs, facial features, and skin, forming an organic whole governed by the dynamic laws of circulation.
The human meridian system consists of three components: primary meridians, collateral meridians, and their associated parts.
1. Primary Meridians
The primary meridians are straight pathways and serve as the main conduits of the meridian system, consisting of three categories: regular meridians, divergent meridians, and extraordinary meridians.
There are twelve regular meridians, also known as the twelve primary meridians, which include the three yin meridians of the hands, the three yin meridians of the feet, the three yang meridians of the hands, and the three yang meridians of the feet. Ancient practitioners, through long-term observation and reasoning, believed that the twelve regular meridians have specific starting and ending points, defined pathways, and connection sequences, exhibiting certain patterns in their distribution and orientation in the limbs, directly related to the organs. They also have an exterior-interior relationship, serving as the main channels for the distribution and nourishment of qi and blood from the heart and lungs to the entire body, as well as being crucial for the dynamic laws of circulation and various physiological functions and self-healing (yin-yang balance) activities.
Divergent Meridians. Ancient practitioners, through long-term observation and reasoning, believed that the divergent meridians are important branches that diverge from the twelve primary meridians, known as the twelve divergent meridians. They originate from areas above the elbows and knees, functioning as a return system that collects blood containing turbid qi produced by the body’s metabolism and sends it back to the heart and lungs for renewal. They also strengthen the connection between the interior and exterior of the twelve primary meridians and supplement areas where the distribution of the twelve regular meridians is insufficient. Although the twelve divergent meridians are the largest branches of the twelve primary meridians, their direction of qi and blood flow differs from that of the twelve primary meridians, yet they still belong to the category of meridians. They facilitate the metabolism of qi and blood throughout the body, ensuring that the blood remains rich in fresh nutrients, which is vital for the dynamic laws of circulation and various physiological functions, as well as for resisting diseases and repairing injuries through self-healing (yin-yang balance) mechanisms.
Extraordinary Meridians consist of eight pathways. Ancient practitioners, through long-term observation and reasoning, identified the extraordinary meridians as: Dumai (Governing Vessel), Renmai (Conception Vessel), Chongmai (Penetrating Vessel), Daimai (Belt Vessel), Yin Qiao Mai (Yin Heel Vessel), Yang Qiao Mai (Yang Heel Vessel), Yin Wei Mai (Yin Linking Vessel), and Yang Wei Mai (Yang Linking Vessel), collectively known as the eight extraordinary meridians. In the dynamic laws of circulation, they play a role in regulating, connecting, storing, and adjusting the qi and blood of the twelve primary meridians. Although the extraordinary meridians do not have a direct relationship with the organs and do not share an exterior-interior relationship, they are closely connected to the twelve primary meridians. Therefore, when the qi and blood of the twelve primary meridians overflow, they can flow into the extraordinary meridians for storage, and when the twelve primary meridians are deficient, the extraordinary meridians can supplement them. Thus, the extraordinary meridians play a regulatory role in the dynamic laws of circulation.
2. Collateral Meridians
Collateral meridians are smaller branches of the primary meridians, which can be classified into bifurcated collaterals, subsidiary collaterals, and superficial collaterals.
Bifurcated Collaterals. Ancient practitioners, through long-term observation and reasoning, believed that bifurcated collaterals are larger branches within the collateral meridian system, diverging from the primary meridians and connecting with neighboring meridians. In the dynamic laws of circulation, they strengthen the connection between the twelve primary meridians and facilitate communication with areas not reached by the primary meridians, thus compensating for their deficiencies. There are fifteen bifurcated collaterals, which include one branch from each of the twelve primary meridians, one from the Renmai, and one from the Dumai, along with the large collateral of the spleen, collectively referred to as the “fifteen bifurcated collaterals.” However, the “Neijing” (Inner Canon) mentions the “large collateral of the stomach, known as Xuli,” which, if included, would result in sixteen bifurcated collaterals.
Subsidiary Collaterals. Ancient practitioners, through long-term observation and reasoning, believed that subsidiary collaterals are the smallest branches of the collateral meridians, distributed throughout the body in countless numbers. As stated in the “Lingshu” chapter on pulse measurement, “The branches of the collaterals are the subsidiaries.” They intertwine and spread throughout the body, forming an organic whole governed by the dynamic laws of circulation. Therefore, subsidiary collaterals, under the influence of the body’s defensive qi, have the functions of “expelling pathogenic factors, facilitating nourishment, warming the flesh, and enhancing the body’s defenses,” thus playing a role in resisting diseases and repairing injuries through self-healing (balancing yin and yang).
Superficial Collaterals. Ancient practitioners, through long-term observation and reasoning, believed that superficial collaterals circulate in the most superficial parts of the body, visible to the naked eye, such as the small superficial vessels. The “Lingshu” chapter on meridians states, “The superficial vessels are those that are visible and floating.” However, their distribution is extensive and lacks specific localization, playing a role in connecting and communicating the meridians and facilitating the flow of qi and blood to the skin surface.
3. Associated Parts
The human meridian system also includes its associated parts. Traditional herbal medicine posits that ancient practitioners, through long-term observation and reasoning, believed that under the influence of the dynamic laws of circulation, the meridians connect internally to the various organs and externally to the muscles and skin, facilitating the exchange of information and energy with the external environment. This connection system includes the tendons and skin.
Tendons (Zongjin) (modern medicine’s nervous system). Ancient practitioners, through long-term observation and reasoning, believed that tendons, in the dynamic laws of circulation, are resilient and strong fibrous tissues that support the body and connect muscles, bones, and joints. They form a system distinct from the meridians that circulates qi and efficiently transmits information and energy between the internal and external environments. Through subsidiary and superficial collaterals, they communicate with the external environment via pores and sweat glands, exchanging information and regulating the balance of internal and external information. The qi circulating in the tendons manifests in forms of “binding, gathering, dispersing, and connecting,” coiling and gathering at the joints, linking the body, and spreading throughout the muscles and chest, with the qi of the tendons connecting to the spirit and ultimately reaching the brain’s essence. As stated in the “Lingshu” chapter on tendons, “The tendon of the foot’s lesser yang meridian runs behind the ear, ascends to the forehead, and converges at the top of the head.” The circulating qi of the tendons nourishes the spirit, supporting, governing, and regulating the body, playing a leading role in stress responses and reflexes, and enabling higher cognitive functions such as memory, thought, and reasoning. Therefore, in the theory of health preservation, traditional herbal medicine emphasizes the practice of closing the eyes to nourish the spirit. During this process, the dynamic laws of circulation of the body and the natural world exchange qi information and energy through the tendon system, resulting in a refreshing sensation and facilitating light and efficient movement. Thus, tendons serve as intermediaries for the exchange of various qi information and energy between the body and the natural world, supporting, governing, and regulating the movement of muscles, bones, and joints, while also playing a role in resisting diseases and repairing injuries through self-healing (balancing yin and yang).
Skin. Ancient practitioners, through long-term observation and reasoning, believed that the skin reflects the physiological and pathological activities of the twelve primary meridians on the body surface, manifesting the dynamic laws of circulation. The distribution areas of the twelve skin regions are based on the surface distribution of the twelve primary meridians, dividing the entire body surface into twelve parts corresponding to the twelve primary meridians. As stated in the “Suwen” (Plain Questions) chapter on the skin, “All twelve primary meridians correspond to the skin regions. To understand the skin regions, one must refer to the meridians, and this applies to all meridians.” Under the influence of the dynamic laws of circulation, the skin serves as the first line of defense against diseases and the first area to sense pathogenic invasions, as stated in the “Suwen” chapter on the skin, “Thus, the onset of all diseases must first occur in the skin and hair.” This reflects the theory of “phenomenological reasoning” in traditional herbal medicine, where specific signs on the skin surface are analyzed to diagnose internal organ and meridian system disorders. For instance, the “Suwen” chapter on the skin states, “If the color is predominantly blue, it indicates pain; if predominantly black, it indicates obstruction; if yellow or red, it indicates heat; if predominantly white, it indicates cold; if all five colors are present, it indicates a balance of cold and heat.” Therefore, the skin plays a special role in the diagnosis and treatment of diseases in traditional herbal medicine, as well as in the dynamic laws of circulation and self-healing (yin-yang balance) mechanisms.