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 the kidney 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 transport waste products and drugs from the blood into the fluid (which becomes urine) as it flows through the tubules. The kidneys also add hormones that maintain blood supply ( erythropoietin), blood pressure, and electrolyte balance.
Disorders that interfere with the transport functions of the cells lining the tubules are called tubular disorders or transport disorders. They include
These tubular disorders are often hereditary and many are present at birth. Some have other causes such as drugs or other diseases.