The Composition and Function of Meridians

The meridian system consists of the twelve primary meridians, eight extraordinary meridians, fifteen collateral meridians, twelve meridian branches, twelve sinew channels, twelve skin areas, and many smaller collaterals and superficial collaterals.

Table 10-1: Composition of Meridians

Meridian	Type	Twelve Primary Meridians	Significance – The meridians associated with the twelve organs, also known as the regular meridians. Function – The main pathways for the circulation of Qi and blood. Characteristics – Divided into three yin and three yang groups for hands and feet, connected to the organs, with corresponding interior-exterior relationships. The circulation starts from the Lung Meridian and ends at the Liver Meridian, continuously cycling, with each meridian having specific acupoints.
Eight Extraordinary Meridians	Significance – Not directly associated with the organs and without corresponding interior-exterior relationships, hence called extraordinary meridians. Function – Strengthen the connections between the primary meridians to regulate the Qi and blood of the twelve meridians. Characteristics – The Ren and Du meridians form a circulation pathway with the twelve meridians, and specific acupoints are associated with them, while the other six meridians do not follow the twelve meridian circulation, with their acupoints attached to the twelve primary meridians.
Twelve Meridian Branches	Significance – Branches that emerge from the primary meridians. Function – Strengthen the connections between the interior and exterior meridians to compensate for the deficiencies in the circulation of the primary meridians. Characteristics – The circulation routes diverge from the limbs, entering the deep body (chest, abdomen) and re-emerging superficially (head, neck).
Twelve Sinew Channels	Significance – The muscular system associated with the twelve primary meridians. Function – Connect the bones and muscles of the limbs, maintaining the network throughout the body, primarily governing joint movement. Characteristics – The circulation direction starts from the distal ends of the limbs towards the trunk, ending at the head and body, without entering the organs, often gathering at the joints and areas rich in muscles.
Twelve Skin Areas	Significance – The skin areas associated with the twelve primary meridians. Function – Connect the skin, enhancing the relationship between the twelve primary meridians and the body surface, serving as the reflection zones of the twelve primary meridians on the skin. Characteristics – The divisions generally correspond to the pathways of the twelve primary meridians on the body surface.
Collaterals	Fifteen Collaterals	Significance – Branches that diverge from the primary meridians and connect to neighboring meridians. Function – Strengthen the connections and regulation between the interior and exterior yin and yang meridians. Characteristics – Each of the twelve primary meridians and the Ren and Du meridians have one collateral, plus the large collateral of the Spleen, totaling fifteen collaterals.
Sun Collaterals – The smallest branches of the collaterals, distributed throughout the body.

(1) Twelve Primary Meridians

The twelve primary meridians refer to the three yin meridians of the hands (Lung, Pericardium, Heart), the three yang meridians of the hands (Large Intestine, San Jiao, Small Intestine), the three yang meridians of the feet (Stomach, Gallbladder, Bladder), and the three yin meridians of the feet (Spleen, Liver, Kidney). As they are affiliated with the twelve organs, they form the main body of the meridian system, hence also called “regular meridians.” The naming of the twelve primary meridians is based on the organs, yin-yang, and the hands and feet. The yang meridians are divided into Shao Yang, Yang Ming, and Tai Yang; the yin meridians are divided into Tai Yin, Jue Yin, and Shao Yin. According to the principle that the organs belong to yin, the bowels belong to yang, the inner side is yin, and the outer side is yang, the names of the meridians are established based on their corresponding organs and their pathways in the limbs. (Table 10-2) The meridians that circulate on the inner side of the limbs belong to yin, while those on the outer side belong to yang. The primary function of the twelve primary meridians is to connect the organs, limbs, and circulate Qi and blood, nourishing the entire body.

Table 10-2: Names of the Twelve Primary Meridians

Yin Meridians (Affiliated with Organs)	Yang Meridians (Affiliated with Bowels)	Circulation Areas (Yin meridians on the inner side, Yang meridians on the outer side)
Hands	Tai Yin Lung Meridian Jue Yin Pericardium Meridian Shao Yin Heart Meridian	Yang Ming Large Intestine Meridian Shao Yang San Jiao Meridian Tai Yang Small Intestine Meridian	Upper Limbs	Front Line Middle Line Back Line
Feet	Tai Yin Spleen Meridian Jue Yin Liver Meridian Shao Yin Kidney Meridian	Yang Ming Stomach Meridian Shao Yang Gallbladder Meridian Tai Yang Bladder Meridian	Lower Limbs	Front Line Middle Line Back Line

The circulation characteristics of the twelve primary meridians are as follows: The meridians belonging to the six organs (five organs plus the Pericardium) are called “yin meridians,” which primarily circulate on the inner sides of the limbs and in the chest and abdomen. The inner sides of the upper limbs are the three yin meridians of the hands, while the inner sides of the lower limbs are the three yin meridians of the feet. The meridians belonging to the six bowels are marked as “yang meridians,” which primarily circulate on the outer sides of the limbs and in the head and body. The outer sides of the upper limbs are the three yang meridians of the hands, while the outer sides of the lower limbs are the three yang meridians of the feet. The distribution pattern of the twelve primary meridians in the head, body, and limbs is: the three yang meridians of the hands and feet are “Yang Ming” in front, “Shao Yang” in the middle (side), and “Tai Yang” in the back; the three yin meridians of the hands and feet are “Tai Yin” in front, “Jue Yin” in the middle, and “Shao Yin” in the back.

The directional pattern of the twelve primary meridians is: “The three yin meridians of the hands start from the chest to the hands, the three yang meridians of the hands start from the hands to the head, the three yang meridians of the feet start from the head to the feet, and the three yin meridians of the feet start from the feet to the abdomen.” (Lingshu: Reversal and Order of Fat and Thin)

The twelve primary meridians form six groups of “collateral relationships” through the connections of branches and collaterals. This means that six groups of “interior-exterior connections” are formed between the yin and yang meridians. Yin meridians are affiliated with the organs, while yang meridians are affiliated with the organs. (Table 10-3).

Table 10-3: Interior-Exterior Relationships of the Twelve Primary Meridians

Hands	Yin Meridians Yang Meridians	Tai Yin Lung Meridian …(Outer Side) Yang Ming Large Intestine Meridian	Jue Yin Pericardium Meridian …(Middle) Shao Yang San Jiao Meridian	Shao Yin Heart Meridian …(Inner Side) Tai Yang Small Intestine Meridian	Interior-Exterior Correspondence
Feet	Yang Meridians Yin Meridians	Yang Ming Stomach Meridian …(Front Side) Tai Yin Spleen Meridian	Shao Yang Gallbladder Meridian …(Outer Side) Jue Yin Liver Meridian	Tai Yang Bladder Meridian …(Back Side) Shao Yin Kidney Meridian	Interior-Exterior Correspondence

The flow order of the twelve primary meridians is: starting from the Lung Meridian → Large Intestine Meridian → Stomach Meridian → Spleen Meridian → Heart Meridian → Small Intestine Meridian → Bladder Meridian → Kidney Meridian → Pericardium Meridian → San Jiao Meridian → Gallbladder Meridian → Liver Meridian, and finally returning to the Lung Meridian. This cycle continues endlessly. (Table 10-4).

(2) Eight Extraordinary Meridians

The eight extraordinary meridians refer to the Ren, Du, Chong, Dai, Yin Wei, Yang Wei, Yin Qiao, and Yang Qiao meridians. Unlike the twelve regular meridians, they are neither directly affiliated with the organs nor have corresponding interior-exterior relationships, hence called “extraordinary meridians.” Their physiological function mainly regulates the circulation of Qi and blood in the twelve meridians.

The Ren Meridian: The meeting point of all yin meridians, hence called “the sea of yin meridians,” which regulates the Qi of all yin meridians in the body.

The Du Meridian is called “the sea of yang meridians,” where all yang meridians converge, regulating the Qi of all yang meridians in the body.

The Chong Meridian is known as “the sea of the twelve meridians,” where all twelve primary meridians converge, playing a role in storing the Qi and blood of the twelve meridians.

The Dai Meridian restrains all meridians. The Yin Wei and Yang Wei meridians regulate the Qi of the six yin and six yang meridians, respectively, to maintain the balance and coordination of yin and yang. The Yin Qiao and Yang Qiao meridians jointly regulate limb movement and the opening and closing of the eyelids.

Most acupoints of the eight extraordinary meridians are located within the twelve primary meridians, with the Ren and Du meridians having their own specific acupoints, thus they are collectively referred to as the “fourteen meridians.”

The fourteen meridians are an important part of acupuncture studies, as they have specific circulation routes and associated symptoms and acupoints for treatment; they are not only the backbone of the meridian system but also the basis for differential diagnosis (diagnosing diseases) and selecting acupoints for treatment in clinical practice. Therefore, it is essential to be familiar with and master the characteristics of the fourteen meridians when studying acupuncture.

(3) Fifteen Collaterals

The twelve primary meridians and the Ren and Du meridians each have a collateral branch, plus the large collateral of the Spleen, totaling fifteen collaterals. The collaterals of the twelve primary meridians emerge from the collaterals below the elbows and knees of the limbs, directing towards their corresponding interior-exterior meridians, meaning that the yin meridian collaterals branch from the yang meridians and vice versa.

The hand Tai Yin collateral branches from the Lie Que point, diverging towards the hand Yang Ming;

The hand Shao Yin collateral branches from the Tong Li point, diverging towards the hand Tai Yang;

The hand Jue Yin collateral branches from the Nei Guan point, diverging towards the hand Shao Yang;

The hand Yang Ming collateral branches from the Pian Li point, diverging towards the hand Tai Yin;

The hand Tai Yang collateral branches from the Zhi Zheng point, diverging towards the hand Shao Yin;

The hand Shao Yang collateral branches from the Wai Guan point, diverging towards the hand Jue Yin;

The foot Yang Ming collateral branches from the Feng Long point, diverging towards the foot Tai Yin;

The foot Tai Yang collateral branches from the Fei Yang point, diverging towards the foot Shao Yin;

The foot Shao Yang collateral branches from the Guang Ming point, diverging towards the foot Jue Yin;

The foot Tai Yin collateral branches from the Gong Sun point, diverging towards the foot Yang Ming;

The foot Shao Yin collateral branches from the Da Zhong point, diverging towards the foot Tai Yang;

The foot Jue Yin collateral branches from the Li Gou point, diverging towards the foot Shao Yang.

The collaterals of the Ren and Du meridians and the large collateral of the Spleen are mainly distributed in the head and body.

The collateral of the Ren Meridian branches from the Jiu Wei point and spreads in the abdomen;

The collateral of the Du Meridian branches from the Chang Qiang point and spreads in the head, diverging towards the foot Tai Yang;

The large collateral of the Spleen branches from the Da Bao point and spreads in the chest and ribs.

The Lingshu states: “All these fifteen collaterals must be seen; if they are deficient, they must be treated. If they are not visible, seek them above and below, as the meridians differ, and the collaterals diverge in different places.” Additionally, there are superficial collaterals that branch from the collaterals and are distributed widely throughout the body.

The twelve collaterals in the limbs strengthen the connections between the interior and exterior meridians of the twelve primary meridians, facilitating the flow of Qi between the interior and exterior meridians, compensating for the deficiencies in the circulation of the twelve primary meridians. The collaterals of the Ren Meridian, Du Meridian, and the large collateral of the Spleen communicate the Qi of the abdomen, back, and the entire body, distributing Qi and blood to nourish all body tissues.

(4) Twelve Meridian Branches

The twelve meridian branches are the divergent parts of the twelve regular meridians that enter, exit, and connect. The twelve meridian branches often emerge from the primary meridians above the elbows and knees of the limbs (diverge), penetrate into the body cavity to connect with the relevant organs (enter), and then emerge superficially to ascend to the head and neck (exit), where the yang meridian branches converge with the primary meridian, and the yin meridian branches converge with the corresponding yang meridian (converge). The twelve meridian branches are grouped into six sets based on their interior-exterior relationships, converging in the head and neck area with the six yang meridians, hence referred to as “the six harmonies.”

The foot Tai Yang and foot Shao Yin branches emerge from the popliteal region, entering the Kidney and Bladder, ascending to the neck, and converging with the foot Tai Yang Bladder Meridian;

The foot Shao Yang and foot Jue Yin branches emerge from the lower limbs, reaching the hairline, entering the Liver and Gallbladder, ascending to the eyes, and converging with the foot Shao Yang Gallbladder Meridian;

The foot Yang Ming and foot Tai Yin branches emerge from the hip area, entering the Spleen and Stomach, ascending to the nose, and converging with the foot Yang Ming Stomach Meridian;

The hand Tai Yang and hand Shao Yin branches emerge from the armpit area, entering the Heart and Small Intestine, ascending to the inner canthus of the eyes, and converging with the hand Tai Yang Small Intestine Meridian;

The hand Shao Yang and hand Jue Yin branches emerge from their respective primary meridians, entering the chest, reaching the San Jiao, ascending to the back of the ear, and converging with the hand Shao Yang San Jiao Meridian;

The hand Yang Ming and hand Tai Yin branches emerge from their respective primary meridians, entering the Lung and Large Intestine, ascending to the supraclavicular fossa, and converging with the hand Yang Ming Large Intestine Meridian.

Due to the characteristics of the twelve meridian branches having divergence, entry, exit, and convergence between the interior and exterior, they not only strengthen the internal and external connections of the twelve primary meridians but also enhance the connections of the meridians affiliated with the organs in the deep body cavity, compensating for the deficiencies in the circulation of the twelve primary meridians. The twelve meridian branches, through the interior-exterior convergence of the “six harmonies,” establish a connection between the yin meridians of the twelve primary meridians and the head, thus expanding the treatment scope of the acupoints of the three yin meridians of the hands and feet. The reason why the acupoints of the three yin meridians can treat diseases of the head and face is closely related to the circulation of the yin meridian branches converging with the yang meridians in the head. Furthermore, the twelve meridian branches strengthen the connections between the twelve primary meridians and the head and face, highlighting the importance and therapeutic effects of the meridians and acupoints in the head and face.

(5) Twelve Sinew Channels

The twelve sinew channels are the system through which the Qi of the twelve primary meridians is distributed to the muscles and joints, forming a muscular system associated with the twelve primary meridians. Their circulation distribution starts from the distal ends of the limbs, converging at the joints and bones, and directing towards the trunk and head. The twelve sinew channels run on the body surface, without entering the organs, and are divided into rigid and flexible sinews. The rigid (yang) sinews are distributed on the neck, back, and outer sides of the limbs, primarily associated with the hand and foot yang meridians; the flexible (yin) sinews are distributed on the chest, abdomen, and inner sides of the limbs, primarily associated with the hand and foot yin meridians. The three yang sinews of the feet start from the toes, ascend along the outer thigh, and converge at the face; the three yin sinews of the feet start from the toes, ascend along the inner thigh, and converge at the abdomen; the three yang sinews of the hands start from the fingers, ascend along the outer arm, and converge at the head; the three yin sinews of the hands start from the fingers, ascend along the inner arm, and converge at the chest.

The sinew channels have the functions of restraining the skeleton, flexing and extending the joints, and maintaining normal movement functions of the body. When there are issues with the sinew channels, it often manifests as cramps, muscle pain, or bi syndrome, and acupuncture treatment usually involves local acupoint selection for reduction, as stated in the Lingshu: “Treatment involves burning needles and puncturing, using knowledge as the number, and pain as the output.”

(6) Twelve Skin Areas

The twelve skin areas are the locations on the body surface where the functional activities of the twelve primary meridians are reflected, and they are also where the Qi of the collaterals is distributed. The distribution areas of the twelve skin areas are based on the distribution range of the twelve primary meridians on the body surface, thus the Suwen states: “To understand the skin areas, one must take the meridians as the basis, and all meridians are like this.”

Since the twelve skin areas are located on the outermost layer of the body and are connected to the Qi and blood of the meridians, they serve as a protective barrier for the body, defending against external pathogens and reflecting disease conditions. Modern clinical practices, such as skin acupuncture and acupoint application methods, are guided by the theory of skin areas.

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