The production of urine to modify plasma makeup is the result of glomerular filtration, tubular absorption, and secretion. Glomerular filtration is the first step of making urine; a process where the kidney filter excess fluid and water products out of the blood in the urine collecting tubules of the kidney, to be eliminated in the body. Tubular reabsorption involves the removal of water and solutes from the tubular fluid which is returned to the circulating blood; while secretion involves the removal of wastes from the body into the bladder, then out through the urethra.