• Kidneys carry out the extremely essential cleansing job of flushing out harmful and poisonous acidic and toxic products. At the same time, they also regulate and maintain the right balance and levels of water, electrolytes and acid base.
What are the functions of the kidney?
The primary function of the kidney is to make urine and purify the blood. Kidney removes waste materials, extra salts and other chemicals which are not required by the body.
Removal of waste products
Purification of blood by removal of waste products is the most important function of the kidney.
The food that we consume contains protein. Protein is necessary for the growth and repair of the body. But as protein is utilized by the body it produces waste products. Accumulation of these waste products is
like poison for the body. Kidney filters blood, and toxic waste products are excreted in the urine.
Creatinine and urea are two important waste products, the amount of which in human body can easily be measured. Their ‘value’ in blood reflects the function of the kidney. When both the kidneys fail, value of
creatinine and urea will be high in blood test.
Removal of excess fluid
The second most important function of the kidney is regulation of fluid balance by excreting extra amount of water as urine and retaining necessary amount of water in the body. So the kidney maintains the right amount of water in the body.
When kidneys fail they lose the ability of removing this extra amount of water as urine.
Excess water in the body leads to swelling.

Balance minerals and chemicals
The kidney plays another important role of regulating minerals and chemicals like sodium,
potassium, hydrogen, calcium, phosphorus, magnesium and bicarbonate; and maintains normal composition of body fluid.
Change in the sodium level can affect sensorium, while change in the potassium level can have serious effects on the rhythm of the heart and functioning of the muscles. Maintenance of normal level of the calcium and phosphorus is essential for healthy bones and teeth.

Control of blood pressure
The kidney produces different hormones (renin,angiotensin, aldosterone, prostaglandin etc) and regulates water and salt in the body, which plays vital role in control of blood pressure. Disturbances in hormone production and regulation of salt and water in a patient of kidney failure causes high blood pressure.

Red blood cells production
Erythropoietin produced in the kidney plays an important role in the production of red blood cells (RBC). In kidney failure production of erythropoietin is less, which in turn leads to decreased production of RBC resulting in low hemoglobin (anemia).

Because of low production of erythropoietin in patients with renal failure the hemoglobin count does not improve inspite of supplementation of iron and vitamins.

To maintain healthy bones
The kidney converts vitamin D into its active form which is essential for the absorption of calcium from food, growth of the bones and teeth, and to keep bone healthy. In kidney failure due to decreased active vitamin D, growth of bones is reduced and they also become weak. Growth retardation may be the first sign of kidney failure in children.

How is blood purified and urine formed?
In the process of blood purification the kidney retains all necessary substances and selectively excretes extra fluid, minerals and waste products.
Let us understand this complex and amazing process of urine formation.
• Did you know that every minute 1200 ml of blood enters in bothkidneys for purification, which is 20% of the total blood pumped by the heart? So in one day 1700 liters of blood is purified!
• This process of purification occurs in small filtering units known as nephrons.
• Each kidney contains about one million nephrons. Each nephron is made up of glomerulus and tubules.
• Glomeruli are filters with very tiny pores with the characteristic of selective filtration. Water and small-sized substances are easily filtered through them. But large-sized red blood cells, white blood cells, platelets, protein etc. cannot pass through these pores. Therefore, in the urine of healthy people large-sized substances are absent.

• First step of urine formation occurs in glomeruli, where 125 ml of minute urine is filtered per minutes. It is quite astonishing that in 24 hours 180 liters of urine is formed! It contains not only waste products, minerals and toxic substances, but also glucose and other useful substances.
• The kidney performs the process of reabsorption with great intelligence. Out of 180 liters of fluid that enters the tubules, 99% of fluid is selectively reabsorbed and only the remaining 1% of fluid is excreted in the form of urine.
• By this intelligent process all essential substances and 178 liters fluid are reabsorbed in tubules and in just 1-2 liters of water, waste products, extra minerals and other such harmful substances are excreted.
• Urine formed by the kidney flows to ureter, and passes through the urinary bladder and is finally excreted out through the urethra.
Can there be variation in the volume of urine in a person with healthy kidney?
• Yes. The amount of water intake and atmospheric temperature are major factors which determine the volume of urine in a normal person.

When water intake is low, urine is concentrated and its volume is less (about 500 ml) but when plenty of water is consumed, more urine is formed.
• In summer because of perspiration caused by high temperature the volume of urine decreases. In winter it is the other way round – low temperature, no perspiration, more urine.
• In a person with a normal intake of water, if the volume of urine formed is less than 500 ml or more than 3000 ml, it is a clear signal that the kidney needs attention and investigation