The process by which nitrogenous wastes are filtered by the Malpighian body is called ultrafiltration. Blood enters the glomerulus through the afferent arteriole. Water, salt, sugar, urea, uric acid, creatinine, hormones, metal ions etc. are filtered from glomerulus under hydrostatic pressure. All these filtrates are called glomerular filtrate or primary urine. Glomerular filtrate accumulates in the capsular space. The hydrostatic pressure of the glomerulus is 70 mm/Hg. Other pressure against this pressure is 35 mm/Hg. As a result, the glomerular filtrate is filtered as the actual filtration pressure (70-35 = 35) is 35 mm/Hg.
For filtration, the capillary wall of the glomerulus and the wall of Bowman’s capsule together form a three-layer filter. The layers that make up the filter are the endothelium layer of the glomerular blood vessels, the basement membrane layer of the glomerular blood vessels and the endothelium layer of Bowman’s capsule. Two kidneys in the human body pump about 1,200 ml of blood per minute and filter about 125 cc of glomerular filtrate.