The kidneys filter and cleanse the blood. They also maintain the body's balance of water, dissolved salts (electrolytes, such as sodium, potassium, and calcium), and nutrients in the blood. The kidneys begin these tasks by filtering the blood as it flows through microscopic tufts of blood vessels with small pores (glomeruli). This process moves a large amount of water and electrolytes and other substances into small tubules. The cells lining these tubules reabsorb and return needed water, electrolytes, and nutrients (such as glucose and amino acids) to the blood. The cells also move waste products and drugs from the blood into the fluid (which becomes urine) as it flows through the tubules as well as add hormones that maintain blood supply (erythropoietin), blood pressure, and electrolyte balance.
Disorders that interfere with the function of the cells lining the tubules are called tubular disorders. Some conditions, called cystic disorders, interfere with these tubular cell functions by causing fluid-filled sacs (cysts) to form and replace or compress normal tubules. Many of these tubular and cystic disorders are hereditary. Of the hereditary disorders, some are detected at birth, and others are not obvious until years later.
Last full review/revision December 2006 by Peter C. Brazy, MD