Kidneys and how they work


The kidneys are bean-shaped organs, about the size of a fist, located on either side of the middle of your back just below your rib cage. Their main role is to filter waste products from your body.

The kidneys and filtration

People obtain the nutrients they need through the food and drink they ingest. The food and drink is broken down in the gastrointestinal system, and the necessary nutrients are absorbed into the bloodstream. The waste products of digestion are excreted in the faeces.

The nutrients in the bloodstream are utilised by your body for energy, growth, repair and maintenance. This process also creates waste products that are deposited back into the bloodstream.

Blood containing waste products enters the kidneys via a major blood vessel — the renal artery. The renal artery then branches into smaller blood vessels, and your blood flows through these tiny vessels to the million or so filtration units within each kidney.

The filtration units, known as nephrons, are where waste products are removed from the blood. The nephrons are also involved in regulating levels of chemicals such as sodium, phosphorus and potassium in the blood, so that they remain within the healthy range.

After being filtered by the kidneys, the waste products and any excess water form urine, which is collected in the bladder. The filtered blood then returns to the rest of the body via the renal vein.

Hormones and the kidneys

As well as the role they play in filtration, the kidneys are responsible for the manufacture of three important hormones, including:

  • erythropoietin, which stimulates your bone marrow to make red blood cells;
  • renin, which helps regulate blood pressure; and
  • the active form of vitamin D, which is needed to maintain healthy bones.

Diseases that affect the kidneys

There are a number of different diseases that can affect the kidneys. Two of the most common are diabetes and high blood pressure.

In people with diabetes, high blood glucose levels can damage the nephrons in the kidneys. This leads to a condition known as diabetic nephropathy, which is a common cause of kidney failure in Australia.

High blood pressure can cause damage to the small blood vessels in the kidneys, and this will interfere with the kidneys’ filtering ability.

Other types of kidney disease include:

  • glomerulonephritis (inflammation of the nephrons);
  • polycystic kidney disease (an inherited disorder where kidney tissue becomes replaced with cysts); and
  • reflux nephropathy (kidney scarring resulting from the backwards flow of urine from the bladder to the kidneys).

Chronic kidney disease affects about one in 9 Australians. Early detection and treatment can significantly improve the outlook for someone with kidney disease.

Last Reviewed: 5 December 2012


1. Kidney Health Australia. All about our kidneys (updated 23 Nov 2012). (accessed Dec 2012).
2. Kidney Health Australia. Fast facts on CKD in Australia (updated 23 Nov 2012). (accessed Dec 2012).
3. National Kidney and Urological Diseases Information Clearinghouse. The kidneys and how they work (updated 23 March 2012). (accessed Dec 2012).


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