‘Ultra filtration’ is the first step in the formation of urine. It is the process wherein substances from the blood brought into the glomerulus are filtered into the Bowman’s capsule of the nephron, through the ultra fine endothelia-capsular barrier or membrane. It is made possible by the high blood pressure in the glomarular capillaries and the osmotic pressure exerted by the contents on either side (glomerular lumen + Bowman capsular lumen) of the endothelia capsular membrane. The glomerular filtrate or primary urine resembles the blood plasma in its chemical composition, except for the high molecular weight (large molecules) organic molecules.
