The Meridians are aligned to the ancient Chinese Five Rhythm system.  

Water controls Kidney and Bladder

Wood controls Liver and Gallbladder

Fire controls four:  Small Intestine, Triple Warmer, Heart and Circulation Sex (or Peridcardium)

Earth controls Spleen and Stomach

Metal controls Lung and Large Intestine

Working with the elements can assist with working on more than one meridian at a time.  For example, working to balance the Water element can help with the kidney and bladder meridians and the organs as well.