The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration.
On an average, 1100 – 1200 ml of blood is filtered by the kidneys per minute.
The glomerular capillary blood pressure causes filtration of blood through 3 layers.
The epithelial cells of Bowman’s capsule called podocytes are arranged in an intricate manner so as to leave some minute spaces called filtration slits.
Blood is filtered so finely through these membranes onto the lumen of the Bowman’s capsule. Therefore, it is considered as a process of ultra filtration.