The kidneys are a pair of vital organs in the human body. The main function of the kidney is to cleanse the system by filtering out impurities and flushing them out of the body as urine. This is the simpler function as far as the kidneys are concerned.

The kidney system has a more complex role and it is responsible for a number of regulatory functions for the well-being of the body.

One important aspect of the kidneys is that they are programmed to detect concentration levels of ions and compounds. These include glucose, creatinine, bicarbonate sodium and a number of others. Therefore, the kidney system acts as a regulator of systems like blood pressure.

In humans the kidneys are located in the abdominal cavity, more towards the back and on either side of the spinal column. However the kidneys are not entirely symmetrically located. The right kidney is slightly lower and smaller than the left kidney. The right kidney is located near the liver, while the left one is near the spleen. Each kidney has an adrenal gland above it, and the each kidney, along with the corresponding adrenal gland, is encased in fat. The fat acts as a cushion to protect the kidneys from injury.

Pain resulting from kidney diseases often manifests as lower back pain. The pain will be felt in the side or flank or in the low back. Kidney pain may also manifest itself as lower abdominal pain. Severe pain in the lower back related to kidney pain has been likened to the pain of childbirth in intensity. Severe pain due to kidney disorders may be accompanied by nausea and vomiting. Sometimes it may be difficult to differentiate between severe lower back pain resulting from kidney related disorders and back pain lower as a result of herniated discs or slipped disc. Nevertheless the pain in the two cases is quite different; that connected to spinal or nerve conditions may cause numbness and weakness in the legs and the patient may find walking and standing very difficult. On the other hand, the burning pain of the kidney related disorders will make the patient writhe in discomfort. During pregnancy, lower back pain is fairly common, but it is generally a heavy and dull ache rather than a severe pain.