A human body is an exceptional machine where a lot of processes (respiration, circulation, digestion, etc.) take place simultaneously. As a result, a lot of waste products produced in our body are in different forms that include carbon dioxide, water, and nitrogenous products like urea, ammonia, and uric acid. In addition to these, the chemicals and other toxic compounds from medications and hormonal products are also produced. A simple diffusion or evaporation will not be sufficient to eliminate the waste from our body.In complex organisms such as animals, including humans, there is a specialized system for excretion called the excretory system.Excretory system in human beingsconsists of a couple of kidneys and ureters, a urinary bladder, and a urethra.Blood contains both useful and harmful substances. Hence, we have kidneys which separate useful substances by reabsorption and toxic substances by producing urine. Kidney has a structural filtration unit called nephron where the blood is filtered. Each kidney contains a million of nephrons. Capillaries of kidneys filter the blood and the essential substances like glucose, amino acids, salts, and required amount of water are reabsorbed. Meanwhile, the pure blood circulates back to other parts. Excess water and nitrogenous waste in humans are converted to urine.Urine thus produced is passed to the urinary bladder via the ureters. The urinary bladder is under the control ofCentral Nervous System. The brain signals the urinary bladder to contract and through the urinary opening called urethra, we excrete the urine.