Twelve meridians is a collective term for the three yin meridians and the three yang meridians of each hand and foot, the same as twelve regular meridians.

There are twelve regular meridians in all in human body (Fig. 12-2). The meridians that pertain to the viscera are yin meridians. The three yin meridians of hand are the lung meridian, heart meridian, and pericardium meridian; and the three yin meridians of foot are the spleen meridian, kidney meridian, and liver meridian. The meridians that pertain to bowels are grouped into yang meridians. The three yang meridians of hand are the large intestine meridian, small intestine meridian, and triple energizer meridian; and the three yang meridians of foot are the stomach meridian, bladder meridian, and gallbladder meridian.

Yin meridians are interior meridians traveling at the yin side of the body and yang meridians are exterior meridians traveling at the yang side of the body, and yin and yang meridians are paired the same way as viscera and bowels. As a result, lung meridian is paired with large intestine meridian; heart meridian is paired with small intestine meridian; pericardium meridian is paired with triple energizer meridian; spleen meridian is paired with stomach meridian; kidney meridian is paired with bladder meridian; and liver meridian is paired with gallbladder meridian.*

Three yin meridians of hand travel from the chest to the hand and link at the finger tips with three yang meridians of hand. Three yang meridians of hand travel from the finger tips to the head where they connect with three yang meridians of foot. Three yang meridians of foot descend from the head to the toe tips where they connect to three yin meridians of foot. Three yin meridians of foot ascend from the toes to the abdomen and chest where they connect with three yin meridians of hand.

All yang meridians of hand and foot reach the head and face. The large intestine meridian of hand yang brightness connects with the stomach meridian of foot yang brightness by the nose wing*; the small intestine meridian of hand greater yang connects with the bladder meridian of foot greater yang at the inner canthus*; the triple energizer meridian of hand lesser yang connects with the gallbladder meridian of foot lesser yang at the outer canthus*.

The spleen meridian of foot greater yin connects with the heart meridian of hand lesser yin at the heart; the kidney meridian of foot lesser yin connects with the pericardium meridian of hand reverting yin at the chest; the liver meridian of foot reverting yin connects with the lung meridian of hand greater yin at the lungs.

Yang brightness meridians of hand and foot travel through the face and forehead; lesser yang meridians of hand and foot travel through both sides of the head; and greater yang meridians of hand and foot circulate through the cheeks and travel through the forehead, vertex* and occipital* region of the head. The heart meridian of hand lesser yin and the liver meridian of foot reverting yin reach the eye; the kidney meridian of foot lesser yin reaches the root of the tongue; and the spleen meridian of foot greater yin reaches the tongue body and scatters under the tongue.

Three yin meridians are distributed along the anterior* sides of the upper limbs* and medial* sides of the lower limbs, and three yang meridians are distributed along the posterior* sides of the upper limbs and the lateral* sides of the lower limbs. Greater yin meridians and yang brightness meridians are distributed on the anterior sides of the lower limbs and the lateral sides of the upper limbs. Lesser yin and greater yang meridians are distributed on the posterior sides of lower limbs and medial sides of the upper limbs, with reverting yin and lesser yang meridians in the middle. However, the spleen meridian of foot greater yin starts and travels posterior to reverting meridian until eight cun above the medial malleolus*.

Three yin meridians of hand emerge from the axilla* and three yang meridians of hand travel through the scapular* region. Of the three yang meridians of foot, stomach meridian travels on the chest and abdomen; bladder meridian travels on the back; and gallbladder meridian travels at the side of the body. All three yin meridians of foot travel on the ventral side*. The meridians traveling through the ventral side from the medial to the lateral are kidney meridian, stomach meridian, spleen meridian, and liver meridian.

Yin meridians connect with the viscera and link with paired bowels, and yang meridians connect with the bowels and link with viscera. As an example, lung meridian of hand greater yin connects with the lungs and links with the large intestine.

Some of the meridians connect with more than two internal organs. For example, the spleen meridian also connects with the heart; the kidney meridian also connects with the liver; the lung meridian, the heart meridian, and the liver meridian also connect with lung and stomach.

The twelve meridians are the main routes for the circulation of qi and blood. Qi and blood flow from one meridian to another in order and in a never ending circle. They start with the lung meridian, go through the large intestine, stomach, spleen, heart, small intestine, bladder, kidney, pericardium, triple energizer, gallbladder meridians, to the liver meridian in the end, 8mpieting the circle, and then flow back to the lung meridian to start another circle.*