Can you explain ultrafiltration to me?

Ultrafiltration is the filtering of blood at the 69000 rmm molecular level. It occurs between the glomerulus and the bowman's capsule in the nephron of the kidney.There are three layers to the filtration;The endothelium of the capillary. there are fenestrations in the endothelium that allow blood plasma and dissolved substances to leave the capillary. (fenestrations are gaps between endothelial cells) The basement membrane. this is composed of a fine mesh of collagen fibres and glycoproteins that ensure no molecule with an rmm over 69'000 can pass though - this explains why blood cells and large plasma proteins cannot pass through to the nephron fluid from the blood in the glomerulus.Epithelial cells of the bowman's capsule and podocytes. These form a filtration barrier that keeps gaps between cells so the fluid components of the filtrate can pass through