Excretion is the process by which metabolic waste products and other non-useful materials are eliminated from an organism. Key organs involved in excretion in humans include the kidneys, which filter blood to remove urea, excess salts, and water, forming urine. The liver detoxifies blood and produces urea. The lungs excrete carbon dioxide and water vapor. The skin excretes sweat, which contains water, salts, and a small amount of urea. Send me the next one 📸