The process of blood filtration starts in the renal cortex which is referred to as the urine manufacturing facility and contains the functional units of the kidneys known as nephrons. Each nephron is supplied with blood from the renal artery via its own individual afferent arteriole. The afferent arteriole enters the glomerulus, which is a bundle of capillaries surrounded by the Bowman's capsule. This is where filtration takes place under pressure. The pressure forces the blood serum through the capillaries, but leaves the blood cells behind. Once the serum crosses the capillary walls it is called filtrate.
The filtrate then enters the renal tubules, which includes the proximal tubule, the Loop of Henle, and then finally, the filtrate leaves the nephrons by means of the collecting duct into the renal pelvis. This then leads to the renal ureters. The ureters then deliver the filtrate that is know called urine into the urinary bladder.