What one needs to appreciate is the vitality that characterizes these channels. They are not only at the center of bringing the “vital” substances to all parts of the body, but they can act as agents that disperse disease through the body.
The channels, themselves, can be diseased giving rise to a number of symptoms: local pain, distension, weakness, numbness, tingling, or weakness. Disease within a channel leads to impaired flow of qi and blood—stagnation—or insufficiency of qi and blood, leading to malnourishment. For instance, attack on the body by pathogenic wind and cold, which, ultimately, enter into the muscle layers can give rise to soreness, stiffness, and aching with points of local tenderness. Prolonged exposure to wind-cold-damp could, very well, give rise to chronic pain or aching in the limbs or joints. Another example, is someone experiencing backpain due traumatic injury, which can give rise rise to pain, aching in the channels. A previous injury or overuse of any part of the body may give rise to stagnation or even deficiency in the channels in some local area, giving rise to aching and pain.
When the zangfu organs are in disharmony, the corresponding channels are likely to manifest symptoms. For example, blood stasis of the heart can give rise to pain that can travel along the Heart channel in arm or rise along the channel to the throat. Excessive heat in the Stomach may give rise to symptoms such hunger or vomiting or it transmit along the Stomach channel in the head, giving rise to bleeding gums, ulcers on the tongue or even tooth abscess.
Liver fire can travel along the Liver channel and manifest as redness, soreness, or pain on the eyes. A most common disorder concerns the Liver and Gallbladder organs. Stagnation of the Liver qi can lead to pain and distention in any portion of the Liver channel. It can even affect its corresponding organ, the Gallbladder and its channel. The genitals, breasts, throat lateral coastal region and head are affected, in this case.
What must be appreciated is how diseases can pass from one organ to another. Heart fire can transmit to the Small Intestine, its interiorly/exteriorly related organ or from the hand taiyang Small Intestine channel to foot taiyang Bladder channel. Another example is how severe deficiency of Kidney yang or impaired transformation of body fluids can cause excessive water to overflow to the Lung and/or Heart. They both are linked to the Kidney via the internal pathway of its primary channel.
Channels can also visibly show disease. In many cases, the course of a diseased channel can be discolored and, therefore visible. Purple usually is indicative of blood stasis, red indicates heat, and pale is associated with deficiency of blood and qi. The purpose of channels is also to help transport acupuncture stimulation from the acupuncture point to the diseased area of the body; this helps to render acupuncture treatment as effective.
A way to regulate the course of treatment of acupuncture is by stimulating the point by some means, like, application of heat, massage, cupping, pressure or even needling.