Urination is the process by which the body expels liquid waste, primarily composed of water, salts, and urea. This waste is produced by the kidneys, which filter blood to remove excess substances. The filtered liquid, known as urine, is stored in the bladder until it is ready to be released. When the bladder fills, nerve signals prompt the urge to urinate. The brain then coordinates the relaxation of the bladder muscles and the contraction of the sphincter muscles, allowing urine to flow out through the urethra. This process is essential for maintaining the body's fluid balance and removing toxins.