To better visualize the concept of chi (qi), and the meridians, think of the meridians as a river-bed, over which water flows and irrigates the land; feeding, nourishing and sustaining the substance through which it flows. (In Western medicine, the concept would be likened to the blood flowing through the circulatory system.) If a dam were placed at any point along the river, the nourishing effect that the water had on the whole river would stop at the point the dam was placed.
The same is true in relation to chi (qi) and the meridians. When chi (qi) becomes blocked, the rest of the body that was being nourished by the continuous flow, now suffers. Illness and disease can result if the flow is not restored.
Acupuncture is one tool used to restore the flow of chi (qi), by inserting needles into the acupuncture points (located on the meridians). These insertions are said to clear any residing blockages, or dams, thus freeing the river to better feed the body in its entirety.
This article was taken from http://www.aworldofchinesemedicine.com/chinese-medicine-meridian-system.htm and modified by Chong International Healing Center