Excretion

Discharge of waste material from the body, including the by-products of digestion, waste products from the repair of tissues, and excess water. The kidneys excrete excess nitrogen in the urine in the form of urea, along with excess water, salts, some acids, and most drugs. The liver excretes bile, which contains waste products and bile pigments formed from the breakdown of red blood cells. Some of the bile is passed from the body in the faeces. The large intestine excretes undigested food, some salts, and excess water in the form of faeces. The lungs discharge carbon dioxide and water vapour into the air. Sweat glands excrete salt and water onto the surface of the skin as a method of regulating the body’s temperature.