HEALTH ADVICE AND SUPPORT:

Kidneys are vital organs that perform a number of functions to clean and maintain the chemical balance in the blood (acidity). Kidneys produce the urine. Understanding how kidneys work may help you keep them healthy.

Functions:
- Clearing waste products and excess fluid
- Balancing the levels of fluids and chemicals
- Producing certain hormones that regulate blood pressure and red blood cells
- Keeping bones healthy

In general, humans are all born with two kidneys.

Kidneys are bean-shaped and fist-sized organs (9 to 12 cm).

Kidneys are located at either side of the mid-spine, just below the chest. See Kidney and urinary system.

Waste products and excess fluid are turned into urine, which passes down a tube called a ureter to the urinary bladder. The urinary bladder stores the urine until it is passed out when you go to the toilet.

Waste products in the blood, such as urea, creatinine and uric acid, are a result of the normal breakdown of active tissues and the food that we eat.

The body uses food as a source of energy and for self-repair. After the body takes what it needs from food, waste products are poured into the bloodstream. If the kidneys did not filter out waste products, these would accumulate in the blood and damage the body.

Urea is produced by the liver as a waste product of protein metabolism and is excreted through the kidneys. Urea is not toxic and increases in blood when there is kidney failure.

Creatinine is a waste product of muscle metabolism that is also excreted through the kidneys. Creatinine is not toxic and increases in blood when there is kidney failure.

Uric acid is a waste product of gene metabolism that is also excreted through the kidneys. Creatinine is toxic; creatinine levels may increase in blood with or without kidney failure. High creatinine levels may produce gout and renal damage, and are associated with high-pressure problems.

Filtration of blood products occurs in nephrons, the small units within the kidney. There are approximately one million nephrons in each kidney. Within each nephron, a capillary is connected to a small urine-collecting tube called a tubule. A complex exchange of chemical products occurs as the waste products and water leave the bloodstream and enter the urinary system.

Imagine that the kidney consisted of one million sieves connected to one million tubes. Sieves filter the blood, and the filtered fluid passes through the tubules, thereby producing urine.

Tubules initially receive the blood filtrate, i.e. a mixture of waste products and chemicals which are useful to the body. Tubules remove and assess the useful chemicals (water, sodium, potassium, calcium, phosphorus, magnesium, and so on) and send them back into the bloodstream and the rest of the body.

Waste products and excess salt and water are excreted. In this way, kidneys regulate the levels of these products. Life depends on a fine balance. Any imbalance will be harmful.

Other kidney functions include:
Acidity regulation (bases of life).
Blood pressure regulation, by managing the volume of water and salt (sodium).

Besides excreting waste products, kidneys also secrete three important hormones: Erythropoietin (EPO), which stimulates the production of red blood cells in the bone marrow.
Renin, which regulates blood pressure.
Calcitriol, the active form of vitamin D, which helps keep calcium within the bones and the normal chemical balance of calcium and phosphorus.

In blood: urea and creatinine, haematocrit, ions and albumin.
In urine: total urine, 24-hour urine protein levels, 24-hour urine microalbumin levels. In blood and urine: creatinine clearance.
Imaging (shape): ultrasound scan, CT scan, and MRI.
Imaging (function): radioisotope scan.