The TCM Explanation
Let's begin with the TCM explanation of Qi flow in acupuncture channels. Acupuncture, the insertion of tiny, hair-thin needles into acupuncture points on the body, stimulates your body's Qi, which then sends signals to the nervous and immune systems telling them how to inhibit pain and resolve disease processes. Qi (pronounced ‘chee') is Chinese word meaning life energy. By Qi, we refer to the energy we use to move our arms and legs, for our organs to perform their functions of breathing, pumping blood and digesting food and for our brain to think. Without Qi, the body is a lifeless corpse.
Like blood, lymph or nerves, qi flows in a vessel system, called acupuncture meridians or channels (the Chinese word for channel is ‘mai' which literally translates as vessel). The channels begin at the ends of the fingers and toes, and travel up the limbs to the torso. In the torso they pass through the various organs, making connections with one another, and then continue on up to the head. We give each channel the name of one of the organs it passes through, such as Lung, Spleen, Bladder or Kidney channel.
Along the channels are acupuncture points. The points are described as wells that reach the river of Qi in the channel below. By inserting a needle into the acupuncture point, the acupuncturist stimulates Qi in the channel. These points have certain functions. A few are analgesic: stimulating LI 4 (Large Intestine 4) has been show by MRI to release endorphins in the brain, natural pain killers.  Some points stimulate the immune system, and some have empirical functions to treat conditions like rashes, constipation or hemorrhoids. Some points clear heat, important for treating infections or toxic conditions, like boils. Others tonify Qi (or energy), used for patients who are tired or weak. The acupuncturist chooses points by both function and location: for example, choosing points near the site of pain, such as the shoulder, knee or back.
Acupuncturists feel that when stimulated, the point sends a signal to the brain to tell the immune system what to do to heal the body. The body has the ability for spontaneous healing. When we get a cut in the skin, a cold, flu or mild headache, or even a bout of food poisoning, the immune system is able to resolve the condition with little or no outside intervention on our part. However, sometimes disease gets more complicated. The immune system can't handle it alone, and we seek outside intervention from a health care professional. Acupuncture needles stimulate Qi in acupuncture points that somehow signal the immune system to tell it what to do to resolve the condition. <BACK TO TOP>
Western Science Explains Acupuncture
Western biomedical science has tried to figure out this ‘somehow'. First, let see what scientists have discovered about the acupuncture points. Acupuncture points are supplied by high concentrations of nerve endings and bundles, mast cells (used for immune function) lymphatics and capillaries.  In addition, acupuncture points have a lower electrical resistance, compared with surrounding skin. Dry skin has a direct current (DC) resistance of about 200,000 to 2 million ohms. Resistance decreases to about 50,000 ohms at acupuncture points.  Acupuncture points can be accurately located with acupuncture point-finders that measure ohms to determine point location. Acupuncture channels show up as a different color than surrounding tissue on photographs taken with infrared imaging. 
Most of the western, scientific research attempting to discover or explain the mechanism of acupuncture has focused on pain relief. Nerve fibers travel from acupuncture points in the extremities to the spinal cord. Then, traveling through the spinal nerve column, they continue on to the brainstem and hypothalamus-pituitary gland. Stimulation of these areas in the brain and spinal cord cause the release of neurotransmitters such as endorphins, norepinephrine and enkephalin that cause inhibition of nerve pain fibers, effectively blocking the transmission of pain sensations. 
B-endorphin is a natural opiate produced in the body, 10-100 times more potent than morphine. It circulates for several hours when released. Dynorphins are an extremely powerful opiate, 200 times stronger than morphine. Dynorphins are released in the spinal cord when electro-stimulation (e-stim) is applied to acupuncture points.
Animal studies have shown that acupuncture can alter the release of various hormones, such as prolactin, oxytocin, luteinizing and growth hormone, and modulate thyroid function. ,[ 8], The effect on hormone release might, in part, explain acupuncture's effectiveness in treating gynecological conditions such as PMS, amenorrhea (no menstrual periods) infertility and perimenopausal syndrome. <BACK TO TOP>
Is Acupuncture Effective?
Resoundingly YES! As early as 1980, the World Health Organization (WHO) published a list of 40 conditions that western, scientific studies have shown are effectively treated with acupuncture. Later, in 1997, The NIH (National Institutes of Health) began endorsing acupuncture treatment with a landmark Acupuncture Consensus Statement.  Here's what the NIH had to say about the efficacy of acupuncture: <BACK TO TOP>
The NIH and WHO Recommend Acupuncture
In a landmark 1997 Acupuncture Consensus Statement the National Institutes of Health (NIH) declared acupuncture safe and recommended it for treatment of a variety conditions:
. . . Both animal and human laboratory and clinical experience suggest that the majority of subjects respond to acupuncture, with a minority not responding . . .
Efficacy for Specific Disorders
. . . There are reasonable studies . . . showing relief of pain with acupuncture on diverse pain conditions such as menstrual cramps, tennis elbow and fibromyalgia. This suggests that acupuncture may have a more general effect on pain . . .
What is the Place of Acupuncture . . . in Comparison or in Combination With Other Interventions?
The data in support of acupuncture are as strong as those for many accepted Western medical therapies.
One of the advantages of acupuncture is that the incidence of adverse effects is substantially lower than that of many drugs or other accepted medical procedures used for the same conditions. As an example, musculoskeletal conditions, such as fibromyalgia, myofascial pain, and tennis elbow, or epicondylitis, are conditions for which acupuncture may be beneficial. These painful conditions are often treated with, among other things, anti-inflammatory medications (aspirin, ibuprofen, etc.) or with steroid injections. Both medical interventions have a potential for deleterious side effects but are still widely used and are considered acceptable treatments. The evidence supporting these therapies is no better that that for acupuncture.
In addition, ample clinical experience, supported by some research data, suggests that acupuncture may be a reasonable option for a number of clinical conditions. Examples are postoperative pain and myofascial [muscle] and low back pain. Example of disorders for which . . . there are some positive clinical trials include addiction, stroke rehabilitation, carpal tunnel syndrome, osteoarthritis and headache. Acupuncture treatment for many conditions such as asthma or addiction should be part of a comprehensive management program.
Many other conditions have been treated by acupuncture; the World Health Organization, for example, has listed more than 40 for which the technique may be indicated.” 
In a landmark 2004 study, the NIH recommended that acupuncture be included in a comprehensive treatment strategy for treating osteoarthritis. “ This trial . . . establishes that acupuncture is an effective complement to conventional arthritis treatment and can be successfully employed as part of a multidisciplinary approach to treating the symptoms of osteoarthritis.”  Dr. Stephan Strauss, director of the National Center for Complementary and Alternative Medicine (NCCAM) reported on CBS's The Early Show :
“For the first time, a clinical trial with sufficient rigor, size, and duration has shown that acupuncture reduces the pain and functional impairment of osteoarthritis of the knee . . . The beauty of this study is that it addresses a major public health problem, and provides evidence that acupuncture is a good option for patients who suffer . . . [acupuncture] does cause significant clinical benefit in reducing pain and allowing people to be more mobile. Anything that can do that is an advantage . . . The lesson is that by applying modern research standards, we can learn from thoughtful practitioners from two thousand years ago instead of dismissing them because they developed their ideas differently.”  <BACK TO TOP>