The Function of The Kidneys

The kidneys have a number of vital roles in the body. Without functioning kidneys it is only possible to survive with renal dialysis. Good renal function is an imperative part of good overall health.

When kidney function deteriorates, patients can develop numerous problems:

  • Fatigue
  • Anaemia – low blood count
  • Oedema – swelling due to fluid retention
  • Shortness of breath
  • Weight loss
  • Confusion and memory loss
  • Vomiting
  • Itchiness
  • Heart rhythm problems

Regulation of Body Fluids

The body requires a particular volume of fluid within it in order to function normally. Most of the fluids which are taken into the body by drinking or eating are excreted by the kidneys to make sure the body does not have too much fluid (fluid over-load) or too little fluid (dehydration).

A relatively small amount of fluid is excreted from the body by sweating, opening bowels and breathing, but most of the fluid excretion occurs by urine production in the kidneys.

Healthy kidneys are extremely good at regulating the amount of fluid in the body. If a person drinks an extra 1.5 litres of fluid in a day, the kidneys will excrete an extra 1.5 litres of urine.

When kidney function deteriorates, there is usually an inability to excrete sufficient fluid resulting in swelling of the feet, hands and face. Patients can also retain excessive fluid in the abdomen causing ascites. Renal failure can also result in excessive fluid in the lungs causing shortness of breath.

Patients whose kidneys do not make sufficient fluids may be treated with diuretics which are medicines that promote fluid production by the kidneys.

Excretion of chemical waste products

The body makes many chemicals which are required for normal functioning. However, there are many chemicals which are normally produced by the body but are not required. Some of these chemical byproducts such as Ammonium and Urea can be harmful if they accumulate in the body and the kidneys excrete these waste products as chemicals in the urine.

The kidneys also excrete excessive acids from the body, thereby maintaining an appropriate acid-base balance which is vital for good health.

If kidneys fail to function normally, waste products accumulate in the body and lead to symptoms, disease and eventually death from kidney failure.

Excretion of medicines

When medicines are taken into the body, they do not stay there indefinitely but are either broken down (often in the liver) or excreted by the kidneys via the urine. If kidneys fail to function normally, medicines may accumulate and cause side effects and harm.

Patients who have poorly functioning kidneys may need to either avoid certain drugs or reduce the usual dosage of a drug so it does not accumulate.

Stimulation of red blood cell production

The kidneys produce Erythropoetin which is a chemical that stimulates the bone marrow to produce red blood cells. Kidney failure is therefore frequently associated with anaemia (lack of red blood cells).

Patients with kidney failure and anaemia can be treated with Erythropoietin which will usually improve the anaemia.

The kidneys also produce various other hormones (such as calcitriol) which are vital for good health.

Control of Blood Pressure

The control of blood pressure is a complex mechanism using a number of organs. The kidneys play a vital role in maintaining a person’s blood pressure. Various kidney diseases can cause high blood pressure, although kidney stone disease does not tend to interfere with blood pressure. Significant pain from kidney stones can affect blood pressure, but this is only temporary and can be seen with all severe pain.

Most people who suffer from high blood pressure (hypertension) do not have this problem from kidney disease as the cause of hypertension is often unknown.
However, poor control of blood pressure over a prolonged period can damage the kidneys and this damage may be permanent.