Excretion in Human Beings The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Kidneys are located in the abdomen, one on either side of the backbone, Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra. How is urine produced? The purpose of making urine is to filter out waste products from the blood. Just as CO, is removed from the blood in the lungs. nitrogenous waste such as urea or uric acid are removed from blood in the kidneys. It is then no surprise that the basic filtration unit in the kidneys. like in the lungs, is a cluster of very thin-walled blood capillaries. Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman's capsule that collects the filtrate.Each kidney has large numbers of these filtration units called nephrons packed close together. 7. Some substances in th...