According to Five Element Theory there are Twelve Meridians in Pairs:
Element Yin Organ Yang Organ
Earth Spleen Stomach
Metal Lungs Large Intestines
Water Kidneys Urinary Bladder
Wood Liver Gallbladder
Fire Heart Small Intestines
Fire (Extra) Pericardium* Triple Burner*
*The Pericardium is the tissue surrounding the heart, while the Triple Burner is a conceptual organ unique to the Chinese medical system.
Below see images of these acupuncture meridians:
