Kidneys rule the 'grasping of the [Qi]'. The [Kidney] acts together with the [Lung] in enabling the deep penetration of inhaled air and energy into the body. Hence the [Kidney] is also called the "root of [Qi]". [Kidney] disharmony may result in respiratory problems, notably chronic asthma.
The [Kidney] is the [Yin Organ] of the element [Water]. It is paired with the [Yang Organ] of [Water], the [Bladder]. The functioning of [Kidney] are therfore vital to the [Water] cycle of the body; in this role it works together with the [Spleen] and [Lung]. The specific role of the [Kidney] is to purify the [Water] it receives from the [Lung], [Small Intestine] and [Large Intestine] and excrete the impure. Dissonance in the [Kidney] may also show up as respiratory problems of the asthma type, hearing difficulties (the sense organ of the [Kidney] is the ear) and hair conditions.
Because the [Kidney] is responsible for the ionic balance of the [Blood], there is also a close connection between the functioning of the [Kidney] and the nervous system. Here [Water] and [Fire] act together, the latter in the coordination of electrical impulses. Ancient texts distinguish [Yin-Kidney] and [Yang-Kidney]. The [Yin-Kidney] is also called the [Water-Kidney] and the [Yang-Kidney] the [Fire-Kidney]. The [Water-Kidney] filters the [Blood] and produces urine, corresponding to the functions of the anatomical kidneys. The [Fire-Kidney] corresponds to the endocrine system: the adrenal glands, sex glands, islets of Langerhans in the pancreas, thyroid and thymus glands and the pituitary gland.