Anatomy and Physiology - The urinary system - Medical Terminology(Adaptive*)

The urinary system is composed of the kidneys, ureters, bladder, and urethra. Its purpose is to regulate the volume and composition of fluids in the body and remove waste substances and excess fluid from the blood.Waste substances are filtered from the blood by the kidneys and excreted in the urine, which exit via the ureters into the urinary bladder. Urine is stored in the bladder until the urge to urinate occurs, at which point the muscles at the bladder outlet relax, allowing the urine to be expelled through the urethra.

The main functions of the kidneys are to regulate the amount of water in the body and keep the body fluids at a constant concentration and acid-base level. They achieve these functions by filtering blood and excreting waste substances and excess water as urine. Other essential substances are reabsorbed into the bloodstream by the process called reabsorption.

The filtering-reabsorption process is necessary to maintain the balance of substances required for a relatively stable internal body environment. This stable internal environment, known as homeostasis, is necessary for the cells of the body to survive and carry out their functions effectively.

If kidneys fail, waste substances cannot be eliminated from the body. Thus, the substances accumulate in the blood to toxic levels and the cells can no longer function. Death ultimately results unless impurities are filtered out of the blood by means of an artificial kidney known as kidney dialysis or the nonfunctioning kidneys are replaced with a healthy kidney through kidney transplantation. (See Figure Urinary system with a cross-section of the right kidney showing internal structures and blood vessels.)


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