well its about the kidneys!

1. Excretion and the Kidneys

6. Ultrafiltration Ultrafiltration occurs in the renal or bowman's capsule. The renal artery which brings blood to the kidney is split up into numerous arterioles, each feeding a nephron. The arterioles split into numerous capillaries which form a knot called a glomerulus. This is surrounded by the bowman's capsule. The arteriole leading into the glomerulus is wider than the one leading out so there is a high blood pressure in the capillaries of the glomerulus. This pressure forces plasma out of the blood by ultrafiltration. Once the blood is filtered in this way only blood cells and the large plasma proteins remain in the blood and continue in to the proximal convoluted tubule.