The urology system starts with the kidneys. Most people are born with two that are located in the back of the abdominal cavity just above the waist, along the spinal column. In adults, each kidney is fist-sized and shaped like a bean.
Via arteries and veins, the kidneys are connected to the body's vascular (blood) system. Every minute, the kidneys receive about 20% of the heart’s output of blood and filter it. This job is done by a huge network of structures known as nephrons, which act as filters, regulating the balance of water, salts and electrolytes. Whatever is not needed is filtered through and eliminated as urine.
The kidneys also:
- maintain normal blood pressure by secreting the hormone renin,
- remove waste products from the bloodstream and producing urine,
- secrete the hormone erythropoietin, which stimulates red blood cell production