Kidneys are bean shaped organs, each about the size of a fist. They are located just above waist level in your back, either side of your spine.

Your kidneys have several important functions. They produce urine, filter waste from your blood, produce hormones, balance your body fluids and salts and adjust levels of minerals and other chemicals so that your body can work properly.

Your body takes all the nutrients it needs from anything you eat or drink. What is left is waste. Some of this waste, as well as natural waste from your body’s metabolism, ends up in the blood and needs to be removed. This is where the kidneys come in.


One of the main functions of the kidney is to act as a filter. The kidney is made up of tiny filters called nephrons.  The average nephron number is approximately 900,000 to 1 million per kidney. Each nephron is made up of a glomerulus and tubule.

The glomerulus acts as a relatively crude filter retaining the larger constituents of blood, such as cells and large molecules.  Water and small molecules pass through the glomerulus and into the tubule. However, if all the water and small molecules were allowed to leave our blood, we would quickly become dehydrated. So, before the kidney excretes the waste products as urine, the tubules reabsorb most of the water and other small but important constituents of the blood that have passed through the glomerulus.  Only then does the kidney excrete the remaining liquid waste as urine.

Healthy kidneys work 24 hours a day 7 days a week to clean the blood. Each day approximately 180 litres of blood are filtered through the kidneys.

The kidneys are usually very effective at their job and it is often only once they have lost 75-80% of their function that symptoms are noticed.


Chronic kidney disease (CKD) is caused by gradual loss of kidney function and may lead to permanent kidney failure, at which point dialysis, or a kidney transplant will be needed.

The Kidney Fund supports the research into kidney disease and diabetes at the South West Thames Institute for Renal Research based at St Helier Hospital, Carshalton, Surrey. The aim of the South West Thames Institute for Renal Research is:

  • To improve the quality of patients’ lives by finding the causes of kidney failure
  • To slow down the process of kidney failure
  • To improve the treatments and ultimately find cures

Benner & Rector’s the Kidney.  Barry M Brenner Saunders;  9th Edition, 2012 

NDT Plus Carmine Zoccali, Anneke Kramer and Kitty J Jager 2010 Chronic kidney disease and en-stage renal disease

About chronic kidney disease:  A guide for patients and their families.
National Kidney Foundation.

Human nephron number:  implications for health and disease.
Bertram JF1, Douglas-Denton RN, Diouf B, Hughson MD, Hoy WE