The six paired meridians are directly related to specific organ systems. While often considered to perform the same functions as they do in western medical thought, in TCM these organs have additional responsibilities. Take a woman’s menstrual cycle, for instance. If there were problems with a women’s cycle, western medicine would look to her hormones or uterus for the cause. In TCM, however, menstrual difficulties could be caused by problems with either the meridians or the organs other than the uterus. The women also has to have enough essences in her kidneys, and enough blood supplied by the liver and spleen. Treating menstrual problem with TCM, therefore, may involve the penetrating and conception meridians, and the kidneys, liver, or spleen. Treatment would endeavour to balance the blood, the essence, or the proportion of yin/yang energy.