 Dear students, in this topic we shall discuss the process of glomerular filtration in detail. The process of urine formation begins with filtration of blood through the glomerular capillaries into the bowman's capsule. In this filtration most of the substances in the blood except the blood cells and the proteins are freely filtered that is it is a process of ultrafiltration. As a result the filtrate obtained has a similar composition to that of blood plasma. This filtration takes place through the glomerular wall which is three layered and is entirely a passive process. Dear students, now we shall discuss the various factors affecting the ultrafiltration. Filtration depends on three factors number one the net hydrostatic pressure number two colloidal osmotic pressure and number three permeability of filtration membrane. The filtration is favored by a hydrostatic pressure difference between the glomerular capillary network and the lumen of the bowman's capsule. The pressure difference between the glomerular capillaries and the lumen of the bowman's capsule is the net hydrostatic pressure which favors filtration. The reason for the high pressure in the glomerulus is that the efferent arterial it has smaller diameter as compared to the afferent arterial which supplies blood to the glomerulus. This is why the smaller efferent arterial diameter presents the resistance to flow of blood. As a result the blood pressure in the glomerulus is high. The blood pressure in glomerulus capillaries is usually 50 mmHg as compared to the peripheral capillaries. So the difference between the 15 mmHg is the net hydrostatic pressure which is favored by the ultrafiltration. Dear students the separation of proteins during the filtration process gives rise to a colloidal osmotic pressure. This pressure opposes filtration. Now we shall discuss the permeability of filtration membrane through which filtrate is formed. The three layered glomerular membrane is a selectively permeable molecular sieve through which all the ultrafiltration takes place. It excludes almost all proteins from the ultrafiltrate and most of the other things go through it. Filtration is based mainly on molecular size. However it also accounts for the shape and charge of molecules. This membrane allows the diluted molecules to be allowed on the size of the membrane. The diluted membrane has a bulk flow of water which carries with it dissolved substances like ions, glucose, urea and many other small molecules that collectively form the filtrate.