Every new jing cycle prompts a new cycle of development. For example, congenital jing exists from conception, carrying on from the jing of the parents. Once a child is born, acquired jing is responsible for replenishing congenital jing and starting the first independent jing cycle which, for the next seven years in girls and eight years in boys, will control growth and development. When the child loses its baby teeth, its body begins the pre-adolescence cycle. The next jing cycle is adolescence, when kidney jing matures and causes the ren meridian to open and flow. At this time, part of the kidney jing transforms into tian gui, which develops and maintains reproductive function. In the next stage physical growth finishes, and eventually declining jing leads to exhaustion of tian gui, thus extinguishing reproductive ability. Inevitably, decline of jing leads to death.