During the production of amino acid energy in the human body, some nitrogenous toxic waste products are produced. The main nitrogenous waste product of humans is urine. The main excretory organ is kidney. Kidney is called the master chemist of the body. 80% of excreta are excreted through the kidneys. The remaining 20% of the excreta is excreted through the accessory excretory organs. The auxiliary excretory organs in the human body are the skin, lungs, liver and digestive tract. The branch of biology that deals with the structure, function and diseases of kidney is called Nephrology.