Glomerular filtration is a passive process in which it is the first step of filtering the blood from the surrounding knot of blood capillaries, from the afferent arteriole and is filtered into the Bowman's capsule, removing wastes from the blood into the Bowman's capsule (nephron). The glomerulus is a very efficient filter than most in the body, the reason for this is because of its filtration membrane (differentially permeable membrane), has a large surface area and is thousand times more permeable to solutes and water.
Blood passing through the Glomerular capillaries is under high pressure because of the proximity of the renal artery to the heart and the narrowing of the efferent arteriole. This means that the Glomerular blood pressure is much higher than that of other capillary beds, resulting in a much higher net filtration pressure, aiding in the process of ultrafiltration.
Net filtration pressure (NFP) is responsible for filtrate formation, involving forces acting at the Glomerulus. Glomerular hydrostatic pressure (HPg), which is essentially Glomerular blood pressure, is the prime force pushing water and other solutes out of the blood and across the filtration membrane or differentially permeable membrane mentioned earlier, into the Bowman's capsule. The filtrates consist of water, salt amino acids, creatine, urea, fatty acids, uric acid, glucose and other vitamins. But blood cells and proteins are not found in the filtrate due to their relative large size. The reasoning for this is molecules smaller than 3 NM in diameter - such as water, glucose, amino acids, and nitrogenous wastes are able to pass freely from the blood into the Glomerular capsule due to their small size, but larger molecules pass with greater difficulty, and those larger than 5 NM are generally unable to enter the tubule. Therefore substances such as proteins can not diffuse over into the Bowman's capsule because of their size, but keeping proteins in the capillaries maintains colloid osmotic pressure, preventing large amounts of water loss to the renal tubules. If the presences of protein or blood cells is in the urine, this usually indicates a problem with the filtration membrane.