urine is formed by the nephrons
Function: Urine Formation and Excretion. Urine is composed of unwanted substances that have been filtered from the blood by nephrons, the functional units of the kidneys.The urine formed in the kidneys passes through the ureters and is temporarily stored in the bladder.unction: Urine Formation and Excretion. Urine is composed of unwanted substances that have been filtered from the blood by nephrons, the functional units of the kidneys.