The kidneys are two bean-shaped organs located on either side of the abdomen, toward the back. Their functions include:

Filtration of blood – They filter urine and waste products of the body’s metabolism from the body. These waste products are toxic to the body, hence the need to eliminate them. The kidneys are the body’s waste management system. NB: Normal colour of urine – After filtration, the filtered content undergoes variety of steps to produce urine. The normal colour of urine is amber (slight yellow colour). When it is deeply yellow or dark in colour, it is concentrated (reflects low body water). When it is as clear as water, it is dilute (excess body water). 

Removal of drugs from the blood – Some of the drugs are broken down by the liver while the waste products are removed by the kidneys. The kidneys also remove some drugs in their original forms without being broken down by the liver.

Removal of excess water from the body – Sometimes, we drink excess water or other liquids. Without the kidneys, this water / liquid will accumulate in the body and cause body swelling. The kidneys recognize excess water in the blood from the fluidity of the blood pumped to them. They then extract as much water as considered to be in excess, returning blood to its normal fluidity. This makes urine to be as clear or almost as clear as water (dilute). 

Retention of water in the body – The kidneys help retain water in the body when there is inadequate water for the body to function well. The need to retain more water is recognized by the thickness of the blood presented to them. They try as much as possible to extract waste products from the blood while returning as much water as possible back into the body. This makes the urine to appear yellow or deep yellow or even dark-coloured (concentrated).

Maintenance of body’s salt balance – The kidneys help to regulate the body’s salt balance (electrolytes). These salts are necessary for optimum body function. Their strict regulation critically depends on normal functioning of the kidneys.

Production of erythropoietin – Erythropoietin is a chemical (hormone) required for red blood cell production. In a normally functioning kidneys, they are released in proportion to deficiency of blood in the body. When the kidneys begin to malfunction, the release of this hormone becomes erratic, depending on the degree of damage, resulting in low blood level (anaemia).