Introduction to Kidney Disease

The major functions of the kidneys are:

Remove waste products and toxins from the blood
Regulate the volume of ﬂuid in the body
Regulate the level of electrolytes in the blood
Regulate the level of other substances in the blood
Regulate blood pH
Secretion of various hormones

If the kidneys become diseased then these functions will not be performed as they should. The degree of dysfunction can vary, from mild to severe, depending on the severity of the kidney disease. Kidney disease can be acute or chronic.

Removal of Waste Products and Toxins from the Blood
The kidneys excrete unwanted substances from the body. Substances such as waste products and toxins are ﬁltered out of the blood, and excreted in the urine.

Creatinine and urea are both waste products in the body. They are produced naturally by the body, but need to be excreted out of the body. Normally the kidney ﬁlters these waste products from the blood, and excretes them in the urine.

However, in severe kidney disease the kidney does not function correctly, and so ﬁltration is impaired. Impaired ﬁltration causes inadequate amounts of creatinine and urea to be ﬁltered. This then leads to increased levels of creatinine and urea in the blood.

Therefore, a blood test for creatinine or urea is very helpful in assessing the kidney function. Creatinine or urea levels that are elevated indicate that there is severe kidney disease.

Regulating the Volume of Fluid in the Body
The kidneys regulate the volume of water in the body. They do this by controlling the volume of urine produced. If there is inadequate ﬂuid in the circulation, the kidney conserves the ﬂuid, and produces concentrated urine. If there is excess ﬂuid in the circulation, then the kidney excretes higher volumes, producing dilute urine.

However, some types of kidney disease cause damage to the glomerulus. Damaged glomeruli are not able to ﬁlter adequately. If there is inadequate ﬁltraotin, then the volume of ﬂuid in the circulation will increase. An excessive volume of ﬂuid in the circulation is called volume overload.

Regulating the Level of Electrolytes in the Blood
The kidneys regulate the amount of electrolytes in the blood. It conserves electrolytes that are deﬁcient, and excretes electrolytes that are in excess.

However, severe kidney disease can cause inadequate ﬁltration, leading to abnormal levels of electrolytes in the blood. The most important of these electrolytes is the level of potassium. If the kidney does not excrete excess potassium adequately, then the potassium level will rise in the blood. High levels of potassium (hyperkalemia) can cause life-threatening cardiac arrhythmias.

Regulating the Level of other Substances in the Blood
The kidneys conserve useful substances, such as valuable nutrients. Protein is a useful substance that the kidney should conserve. However, kidney disease can cause proteins to be excreted into the urine. Protein in the urine is called proteinuria.

Regulating Blood pH
The kidneys contribute to the regulation of blood pH by excreting hydrogen ions (which are acid) and reabsorbing bicarbonate ions (which are alkaline).

However, in severe kidney disease there may be inadequate amounts of hydrogen ions excreted, leading to an accumulation in the blood. Furthermore, there may be inadequate amounts of bicarbonate ions reabsorbed. This can result in a condition called metabolic acidosis.

Secretion of Hormones
The kidneys secrete some important hormones, such as renin, erythropoietin and calcitriol. However, in severe kidney disease there may be abnormal amounts of hormones produced.