Essence, which is also called "essential qi" or jing is considered to be the underpinning of all aspects of organic life. Stored in the kidneys, it is the material basis for all kinds of functional activities and is responsible for human growth and development. In effect, kidney essence is what makes up our human vitality. The stored essence is comprised of congenital jing (also called congenital essence) and acquired jing (also called acquired essence).

Congenital jing:
Congenital jing originates from the kidney itself and is made from the sexual energies of the parents when they procreate. Thus, "congenital jing" forms the basis for prenatal growth in the womb and nourishes the developing embryo and fetus. It also determines the constitution and characteristics a person will have throughout their life. After birth, congenital jing is stored in the kidneys and is nourished by acquired jing. It gradually becomes the material for our development and reproduction. Thus it also sometimes referred to as "reproductive jing."

Acquired jing:
Acquired jing is often called the "jing of the organs" because this jing originates from them. It is obtained from ingested foods and fluids through the action of the stomach and spleen. The digested food and fluids are first transformed into nutrient substances in the stomach, and then further transformed into nutrient essence by the spleen. This nutrient essence or acquired jing is mainly responsible for irrigating and nourishing the organs so they can maintain their daily functions. Extra-acquired jing that is not being used is stored in the kidneys and can be used for nourishing the organs on demand. This process results in acquired jing being repeatedly replaced in the kidney; the extra jing is stored, sent out as required, and then replaced by new jing.