In both traditional Chinese medicine (TCM) and western medicine, the kidneys have many functions. This article - What is the 'Kidney' - aims to describe the traditional functions of the Kidney with modern-day observations and understanding.
- The Kidney is the root of Qi and the foundation of Yin and Yang [1,2]
Traditional Chinese Medicine
In TCM, all the bodily systems rely on the Kidney for Qi, for the energy to function. It also maintains a balance between the Yin and Yang energies in the body, and within each organ system.
For example, if the Kidney has become deficient in Yin energy, this will affect the Yin aspect of other organs. In this case, some organ systems may seem unable to ‘switch off’ or find the balance between functioning and being overactive. Similarly, if the Kidney is deficient in Yang energy, this will affect the Yang aspect of other organs.
Some organ systems will then seem sluggish, unable to find the energy to function properly. The Kidney is typically the root of many imbalances.
In western medicine, the adrenal glands are known to sit on top of the kidneys and secrete stress hormones; cortisol, epinephrine (adrenaline), and norepinephrine (noradrenaline).
The body has a natural daily rhythm of cortisol secretion, a peak in the morning gives the body energy to wake, dropping to its lowest during the night. When under stress, epinephrine and norepinephrine are secreted, causing a surge of energy; increased heart rate, blood pressure, and glucose metabolism - the fight or flight response.
The kidneys control the homeostasis of the body by determining our response to stress, detecting and adjusting blood pressure, balancing the levels of water in the body, and maintaining the normal pH of the blood.
The kidneys continuously calibrate and regulate our bodies to adapt to our internal and external environments. This could be likened to the Yin and Yang balance described in the traditional texts. The ability of the kidneys to provide us with the energy to remain alert, and provide us with a boost of energy when we need it, could be what the authors of the traditional texts observed and the reason they labelled the Kidney as the root of Qi.
2. The Kidney stores Essence ‘Jing' [1,2]
Traditional Chinese Medicine
In TCM, Essence is a type of energy or substance that is inherited from your parents and drives physical and mental development, maturity, and reproduction. [1,2]
The health and habits of parents at conception and during pregnancy, will affect the health of the child. Essence naturally declines over time, and how we live our lives determines how long this Essence lasts.
This may correlate to the general vitality of the body which declines naturally over a lifetime, at a rate that usually depends on our lifestyle. If we live in a way that overworks the body and mind, the Essence is used up quickly and we will age quicker.
Living with chronic stress increases blood pressure and blood sugar, which can lead to kidney damage. In modern medicine, physical development is driven by growth hormones. Kidney function drives proper growth and development in a number of ways:
- Removes waste from the blood to enable the body to process growth hormone 
- Maintains the balance of minerals calcium and phosphorus for proper bone development 
- Maintains the pH of the blood, creating the right conditions for growth 
- If kidney function is poor, a low appetite can leave a child malnourished and lacking nutrients needed for proper growth 
- The kidneys produce erythropoietin, a hormone that signals the bone marrow to create red blood cells, essential for growth 
- Maintains fluid balance, for the right conditions for growth 
Poor kidney function typically delays growth in children due to a combination of all the above factors not functioning correctly. The functions of the adrenal glands, which sit on top of each kidney, seem to correlate to many traditional functions of the Kidney.
The adrenal glands secrete cortisol, the stress hormone, which when in excess stunts the normal growth and development of the brain.
The adrenal glands also secrete sex hormones androgen and estrogen, that drive early sexual development. The ovaries and testicles produce a larger amount of these hormones once they mature.
Poor kidney function negatively affects fertility due to the loss of the pulses of gonadotropin release hormone from the hypothalamus which disrupts the normal cycle of luteinising hormone and follicle-stimulating hormone release. The loss of this cycle causes menstrual issues, sexual dysfunction, and infertility in both sexes.
Health, vitality, and resilience, could be synonymous with Essence and is seen when the body is properly nourished with balanced nutrients and minerals, oxygen, has proper removal of waste, and healthy cortisol levels, all controlled by the kidneys.
- The Kidney controls fluids 
Traditional Chinese Medicine
In traditional Chinese medicine (TCM), the Kidney controls fluids. (2) This is very similar to their function in western medicine. TCM also recognises that the Kidney plays a role in all fluid secretions, including semen and vaginal fluids.
In western medicine, the kidneys filter the blood and remove waste. Swelling of the face and extremities - hands, arms, feet, and legs, caused by the build-up of water in the body is called edema and can happen when the kidneys aren’t working efficiently, although this isn’t the only cause. (9)
The adrenal glands, on top of the kidneys, produce aldosterone. Aldosterone is a hormone that regulates the levels of sodium and potassium in the blood, by causing reabsorption of sodium and water and excretion of potassium by the kidneys. This maintains water levels in the body, the pH of the blood, and regulates blood pressure. (3)
One study found that men with chronic kidney disease (CKD) had poor sperm quality, volume, and zinc deficiency, an essential mineral for sperm health that is frequently deficient in people with CKD. (9)
In women with CKD, ovarian dysfunction is common. (10) High levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin are frequently seen, disrupting the HPG axis causing the decline and eventual absence of estrogen. (11)
Estrogen is essential in the production of vaginal fluids and women with declining kidney function may suffer from early menopause and associated symptoms such as lack of menstruation, anovulation, dry skin and hair, and vaginal dryness. (10)
The kidneys in both TCM and western medicine are vital for maintaining water metabolism as well as the hypothalamic, pituitary, and gonadal (HPG) axis which is involved in the production of various bodily fluids.
4. The Kidney receives Qi from the Air 
Traditional Chinese Medicine
This one is tricky, surely that's the Lung's job? In TCM, the Kidney and Lung are closely connected. When we breathe in, the Lung sends Qi and fluids downward to the Kidney. The Kidney holds the Qi and sends fluids as vapour back up to the Lung to keep them moist.[1,2]
In Western medicine, the kidneys and lungs are the main moderators of the body's acid-base or pH level. The lungs can increase or decrease pH levels by adjusting the amount of carbon dioxide exhaled. The kidneys reabsorb or excrete bicarbonate and fixed acids as needed.
The Kidney's role of receiving Qi from the air may be synonymous with its western medicine role of maintaining the correct pH of the blood. This ensures that blood cells carry enough oxygen for the body's needs and that all biochemical processes and proteins can function properly (the body has enough Qi energy).[12,13]
5. The Kidney governs Bones, produces Marrow, and manufactures Blood
Traditional Chinese Medicine
In TCM, the Kidney is at the root of all bone-related issues. The Kidney nourishes the Marrow which fills the Bones and in TCM, the brain is described as the sea of Marrow. In both TCM and western medicine, marrow is involved in the manufacturing of blood.
These Kidney functions are reflected in western medicine as the kidneys produce vitamin D, bone morphogenic protein-7 (BMP-7), and regulate calcium and phosphate levels (essential for the development and metabolism of bone). The kidneys also produce erythropoietin, a hormone that acts on the stem cells in the bone marrow to stimulate the production of red blood cells.
It is clear that the kidneys play a large role in bone and blood health in both TCM and western medicine.
6. The Kidney manifests in the head hair
7. The Kidney opens into the ears
8. Houses will-power
- Ni M. The yellow emperor's classic of medicine: a new translation of the neijing suwen with commentary. Shambhala Publications; 1995.
- Maciocia G. The Foundations of Chinese Medicine E-Book: A Comprehensive Text. Elsevier Health Sciences; 2015. 155-157 p
- John Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; 2020. Adrenal Glands [Date cited 07/04/2020]. Available from: https://www.hopkinsmedicine.org/health/conditions-and-diseases/adrenal-glands
- You and your hormones [Internet]. Society of endocrinology. Cortisol; Jan 2019 [Date cited 07/04/2020]. Available from: https://www.yourhormones.info/ormones/cortisol/
- National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc, 2020. Stress and your Kidneys [Date cited: 28/04/2020]. Available from: https://www.kidney.org/atoz/content/Stress_and_your_Kidneys#
- National Scientific Council on the Developing Child, 2005/2014. Excessive Stress Disrupts the Architecture of the Developing Brain: Working Paper 3. Updated Edition. Available from: http://www.developingchild.harvard.edu
- National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. United States: National Institutes of Health; n.d. Growth Failure in Children with Chronic Kidney Disease; 2014 [Date cited: 28/04/2020]. Available from: https://www.niddk.nih.gov/health-information/kidney-disease/children/caring-child-kidney-disease/growth-failure-chronic-kidney-disease
- Ahmed SB, Vitek WS, Holley JL. Fertility, contraception, and novel reproductive technologies in chronic kidney disease. InSeminars in nephrology 2017 Jul 1 (Vol. 37, No. 4, pp. 327-336). Available from: https://doi.org/10.1016/j.semnephrol.2017.05.004
- Lehtihet M, Hylander B. Semen quality in men with chronic kidney disease and its correlation with chronic kidney disease stages. Andrologia. 2015 Dec;47(10):1103-8. Available from: https://doi.org/10.1111/and.12388
- Ahmed SB, Ramesh S. Sex hormones in women with kidney disease. Nephrology Dialysis Transplantation. 2016 Nov 1;31(11):1787-95. Available from: https://doi.org/10.1093/ndt/gfw084
- Female sexual dysfunction in renal failure. US National Institutes of Health: U.S. National Library of Medicine; 2017 [cited 16/02/2021]. Available from: https://clinicaltrials.gov/ct2/show/NCT03172637
- Sorino C, Scichilone N, Pedone C, Negri S, Visca D, Spanevello A. When kidneys and lungs suffer together. J Nephrol. 2019 Oct;32(5):699-707. doi: 10.1007/s40620-018-00563-1. Epub 2018 Dec 6. Erratum in: J Nephrol. 2019 Sep 16;: PMID: 30523563. Available from: https://pubmed.ncbi.nlm.nih.gov/30523563/
- Hopkins E, Sanvictores T, Sharma S. Physiology, Acid Base Balance. [Updated 2021 Sep 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507807/
- Wei K, Yin Z, Xie Y. Roles of the kidney in the formation, remodeling and repair of bone. J Nephrol. 2016;29(3):349-357. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4879154/