The kidneys begin these tasks by filtering the blood as it flows through microscopic tufts of blood vessels with small pores (called 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.
The cells lining the tubules add hormones that maintain blood supply ( erythropoietin), blood pressure, and electrolyte balance and also make an enzyme that activates vitamin D ( calcitriol). When in its active form, calcitriol is able to help regulate calcium and phosphorus and maintain healthy bone.
Disorders that interfere with the function of the cells lining the kidney's tubules are called tubular disorders. Some tubular disorders are hereditary, or congenital. Of these congenital tubular disorders, some are detected in the first year of life, and others are not obvious until years later.
Congenital tubular disorders include the following: