Describe excretory system in human beings …

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 of Central Nervous System. The brain signals the urinary bladder to contract and through the urinary opening called urethra, we excrete the urine.