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The urinary system, also known as the renal system, consists of the kidneys, ureters, bladder, and the urethra. Each kidney consists of millions of functional units called nephrons. The purpose of the renal system is to eliminate wastes from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The kidneys have extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Following filtration of blood and further processing, wastes (in the form of urine) exit the kidney via the ureters, tubes made of smooth muscle fibers that propel urine towards the urinary bladder, where it is stored and subsequently expelled from the body by urination (voiding). The female and male urinary system are very similar, differing only in the length of the urethra. 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. 8002,000 milliliters (mL) of urine are normally produced every day in a healthy human. This amount varies according to fluid intake and kidney function. ==Structure== The urinary system refers to the structures that produce and conduct urine to the point of excretion. The human body normally has two paired kidneys, one on the left and one on the right. Urine is formed by nephrons, the functional unit of the kidney, and then flows through a system of converging tubules called collecting ducts. The collecting ducts join together to form minor calyces, then major calyces, which ultimately join the pelvis of the kidney (renal pelvis). Urine flows from the renal pelvis into the ureter, a tube-like structure that carries the urine from the kidneys into the bladder. During urination, urine stored in the bladder is discharged through the urethra. In males, the urethra begins at the internal urethral orifice in the trigone of the bladder, continues through the external urethral orifice, and then becomes the prostatic, membranous, bulbar, and penile urethra. Urine exits through the external urethral meatus. The female urethra is much shorter, beginning at the bladder neck and terminating in the vaginal vestibule. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Urinary system」の詳細全文を読む スポンサード リンク
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