Kidney and urinary tract disorders can involve one or both kidneys, one or both ureters, the bladder, or the urethra, and in men, the prostate, one or both testes, or the epididymis. Problems with the male reproductive system often manifest as scrotal pain, scrotal swelling, blood in the semen, or persistent erection.
Evaluation for a kidney or urinary tract disorder begins with a medical history and physical examination. Doctors sometimes need to do tests or procedures to diagnose a kidney or urinary tract disorder.
Blood flow to the kidneys needs to be intact for the kidneys to function properly. Any interruption of or reduction in the blood flow can cause kidney damage or dysfunction and, if long-standing, increased blood pressure ( hypertension). When blood flow in the arteries supplying the kidneys is completely blocked, the entire kidney or a portion of the kidney supplied by that artery dies (kidney infarction). Kidney infarction can lead to the inability of the kidneys to process and excrete the body's waste products ( kidney failure).
Most bladder cancers arise from the cells that form the innermost layer of the bladder. These cells, called transitional cells or urothelial cells, allow the bladder to stretch when it is full and shrink when it is emptied. Transitional cells are also the type of cells responsible for most cancers of the renal pelvis and ureters.
The kidneys constantly produce urine, which flows through 2 tubes (the ureters) to the bladder, where urine is stored (see figure Viewing the Urinary Tract). The lowest part of the bladder (the neck) is encircled by a muscle (the urinary sphincter) that remains contracted to close off the channel that carries urine out of the body (the urethra), so that urine is retained in the bladder until it is full.
Each kidney contains about 1 million filtering units (glomeruli). The glomeruli are made up of many microscopic clusters of tiny blood vessels (capillaries) with small pores. These blood vessels are designed to leak fluid from the bloodstream into a system of miniature tubules. The tubules secrete and reabsorb chemicals and substances from the fluid to cause it to become urine. The urine then drains from the tubules into larger and larger tubes until it leaves the kidney. Normally this filtering system permits fluid and small molecules (but almost no protein or blood cells— Asymptomatic Proteinuria and Hematuria Syndrome) to leak into the tubules.
In healthy people, urine in the bladder is sterile—no bacteria or other infectious organisms are present. The tube that carries urine from the bladder out of the body (urethra) contains no bacteria or too few to cause an infection. However, any part of the urinary tract can become infected. An infection anywhere along the urinary tract is called a urinary tract infection (UTI).