Kidney and bladder health

12 March 2009

The normal function of the kidneys

It's very simple: no kidneys, no life. They are your body's tireless waste removers. They deserve a closer look on World Kidney Day.

It's very simple: no kidneys, no life. They are your body's tireless waste removers. They deserve a closer look on World Kidney Day.

Measuring renal function
The glomerular filtration rate (GFR) is used as a tool to measure your renal function. It is derived from blood and urine tests. This involves collecting and assessing all urine passed in a 24-hour period. Symptoms of renal failure may only appear when more than 50 percent of renal function is lost. By then the disease is often very advanced. The normal GFR of women is lower than that of men and GFR declines with age. Pregnancy may also influence your GFR.

Main functions of your kidney – job description of the kidneys

  • Removing wastes and excess water.

  • Maintaining the chemical balance of your body.

  • Producing important hormones.

Tireless waste remover
Your kidney processes 180 liters of blood daily to sift out two to three liters of waste product and water, called urine.

A chemical balancing act
Normal kidneys have the ability to regulate blood volume and composition according to the body’s needs. The kidneys perform this vital function by acting as a constant gauge, controlling the chemical content, concentration and acidity by changes in the urinary excretion.

  • Erythropoietin that stimulates the bone marrow to make more red cells. Red cells carry the oxygen in your blood. Anaemia is common in patients with chronic renal failure.

  • Renin is an enzyme that helps to control blood pressure. It is released when blood pressure is low, which causes blood vessels to narrow and blood pressure to increase.

  • Vitamin D(3) is the active form of Vit D and helps to regulate calcium and phosphate levels in the blood. This is important for the formation of bone and for the chemical balance in the body.

Small margin of error
Build-up of excess fluid or toxic waste products in your blood is very dangerous and can be life threatening. The kidneys remove this waste and water that would otherwise be damaging to your body. Regulating blood volume is important for your blood pressure and the workload on your heart. Biochemical reactions require a specific pH level or ion concentration. The correct levels of potassium, calcium and other electrolytes or minerals are essential for the body to function. Therefore both the volume and the composition of body fluid must be controlled.

Part of a detoxification system
The urinary system is a vital part of your body’s cleansing systems. These include the lungs, skin and intestines. All these organs excrete waste and water to maintain your chemical and fluid balance in the body. The kidneys play a vital role in maintaining an environment that is optimal for the cells of your body.

Dipstick test
Fortunately doctors don’t have to rely on taste to test urine any more. A urine test is part of the routine evaluation of patients and the urine dipstick is an inexpensive tool that can allude to kidney problems. The physical appearance, colour and smell of the urine are also important. Changes in the filtration barrier of the glomerulus can cause bigger molecules like protein to be sifted out and be detected in the urine. This is called proteinuria. Problems with the capillaries of the glomerulus can cause haematuria, where blood cells are detected in the urine. Urine can also be sent to a laboratory for microscopic examination and tests.

Blood tests
If your doctors are concerned about the wellbeing of your kidneys, they can perform blood tests which can determine the level of urea and creatinine in your blood.

Written by Dr K. Coetzee, reviewed by Dr R. Moosa, head of the Renal Unit, Tygerberg Academic Hospital.


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