The kidneys are subject to numerous
disorders. Some, present at birth, are called developmental and
hereditary abnormalities;
some arise as a result of uncontrolled cell growth and are called tumors. The majority of
disorders occur secondary to physiologic, anatomic, metabolic, or immunologic alterations within the body, or to toxic or infectious agents acquired from the environment. For instance, preliminary studies have shown a link in some patients between the overuse of ibuprofen and acetaminophen, two common painkillers, and kidney failure. Kidney disorders can be categorized according to the anatomic site they involve: those interfering with the blood flow of the kidneys, those directly damaging the nephrons (the functional units of the kidneys), and those obstructing the outflow of urine from the kidneys.
Developmental and
Hereditary Abnormalities
Congenital abnormalities of size, shape, and number of the kidneys are quite common. These abnormalities cause problems only if they interfere with the passage of urine. A rather devastating hereditary condition is adult polycystic kidney disease. The kidneys become filled with large cysts, and the disease usually becomes apparent in the fourth or fifth decade of life. Scientists have determined the general location of the gene responsible.
A more unusual condition is hereditary nephritis, the most common variety being Alport syndrome. Red blood cells and protein are present in the urine, deafness frequently develops, and progressive loss of renal function occurs. There are several hereditary renal tubular functional defects (the Fanconi syndrome) involving excretion of amino acids, monosaccharides, phosphate, and hydrogen ions; the Fanconi syndrome does not usually lead to renal failure.
Tumors
The two important malignant tumors of the kidney are Wilm tumor, which occurs primarily in the early years of life, and hypernephroma (renal cell cancer), which is more common in later years. Wilm tumor occurs as a painful abdominal mass. Patients with hypernephroma may have red blood cells in their urine, pain and a mass in their sides. Surgical excision of these tumors is curative if it is done before they spread outside of the kidney.
Disorders of Renal Blood Flow
A decrease in renal blood flow may be secondary to primary (prerenal) events, including a reduced cardiac output (such as in heart failure), a decreased blood volume (hemorrhage or dehydration), decreased blood pressure, or hypotension (as in shock from severe infection). Correction of the primary event allows renal function to return to normal. Disease of the renal arteries also reduces renal blood flow, thereby decreasing renal function. Arteriosclerosis of the renal arterioles, due to severe hypertension, may rapidly reduce renal blood flow and impair renal function. Toxemia of pregnancy and thrombosis of the renal veins also may cause renal failure.
Disorders Directly Damaging the Nephrons
Each nephron in the kidney is composed of a glomerulus and its tubule. Some diseases, such as glomerulonephritis, primarily attack the glomerulus; others attack the tubulointerstitial parts of the kidneys. Acute glomerulonephritis may occur one to three weeks after a streptococcal skin infection or an upper respiratory tract infection and is manifested by scanty urine, red blood cells in the urine, edema, hypertension, and impaired renal function. The majority recover completely. Systemic diseases such as diabetes mellitus, multiple myeloma, and amyloidosis also may cause damage that can progress to renal failure.
The causes of tubulointerstitial disease of the kidneys are even more numerous. Acute tubular necrosis (cell death) is caused by toxic substances, circulating blood or muscle pigments, or shocklike states. It is an acute reversible form of renal tubular cell damage that is quite common. Interstitial nephritis may be due to toxic agents (analgesics, antibiotics, heavy metals), metabolic abnormalities (high levels of calcium or uric acid in the blood), infectious diseases (bacterial pyelonephritis, infectious mononucleosis), hypersensitivity reactions to drugs (sulfonamides, penicillins), vascular lesions (arteriosclerosis, sickle-cell disease), obstruction of urine flow (kidney stones), tumors (leukemia, lymphoma), and hereditary disorders (familial nephritis). Hemolytic uremia syndrome, a rare disease that is the most common cause of kidney failure in infants, was found to be caused by a particular form of the bacterium Escherichia coli.
Disorders Obstructing the Urine Outflow
Obstruction of the urinary tract that causes blockage of the outflow of urine leads to renal damage. Numerous types of lesions can cause obstruction, such as congenital malformations and hereditary disorders (for example, cysts), infectious processes causing strictures (tuberculosis in the kidneys, gonorrhea in the urethra), stones, and tumors. Bladder dysfunction due to a neurologic lesion and bladder outlet obstruction due to prostatic hypertrophy also are common obstructive events. Some lesions lead to acute and others to chronic renal failure.
End Stage Renal Failure
When there is complete loss of renal excretory function, toxic wastes build up in the body and cause uremia. If untreated, patients may die from such complications as infection, hemorrage, congestive heart failure, or hypertension. Patients may be kept alive by either hemodialysis or peritoneal dialysis, or by receiving a renal transplant. A kidney transplant may be obtained from a living donor, usually a family member or close friend, who may donate one of their two normal kidneys. Alternatively a kidney may be obtained from someone who has just died. Approximately 90% of transplanted kidneys are functioning one year after surgery.