Bodily process for disposing of undigested food waste products and nitrogenous by-products of metabolism , regulating water content, maintaining acid-base balance, and controlling osmotic pressure to promote homeostasis .
It refers to both urination and defecation and to the processes that take place in the digestive and urinary system s, as the kidney and liver filter wastes, toxins, and drugs from the blood and food reaches the last stage of digestion. Ammonia from protein digestion, the primary excretory product, is converted to urea to be excreted in urine .