Urinary system
The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The urinary tract is the body's drainage system for the eventual removal of urine.[1] The kidneys have an extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Each kidney consists of functional units called nephrons. Following filtration of blood and further processing, wastes (in the form of urine) exit the kidney via the ureters, tubes made of smooth muscle fibres that propel urine towards the urinary bladder, where it is stored and subsequently expelled from the body by urination. The female and male urinary system are very similar, differing only in the length of the urethra.[2]
This article is about the human urinary system. For urinary systems of other vertebrates, see Urinary systems of birds, urinary systems of reptiles, and urinary systems of amphibians.Urinary system
Urine is formed in the kidneys through a filtration of blood. The urine is then passed through the ureters to the bladder, where it is stored. During urination, the urine is passed from the bladder through the urethra to the outside of the body.
800–2,000 milliliters (mL) of urine are normally produced every day in a healthy human. This amount varies according to fluid intake and kidney function.
History[edit]
Kidney stones have been identified and recorded about as long as written historical records exist.[10] The urinary tract including the ureters, as well as their function to drain urine from the kidneys, has been described by Galen in the second century AD.[11]
The first to examine the ureter through an internal approach, called ureteroscopy, rather than surgery was Hampton Young in 1929.[10] This was improved on by VF Marshall who is the first published use of a flexible endoscope based on fiber optics, which occurred in 1964.[10] The insertion of a drainage tube into the renal pelvis, bypassing the ureters and urinary tract, called nephrostomy, was first described in 1941. Such an approach differed greatly from the open surgical approaches within the urinary system employed during the preceding two millennia.[10]