The three filtration barriers that substances must pass through when leaving the blood and entering the tubule lumen are the glomerular capillary endothelium, the epithelium of Bowman's capsule, and which other structure?

Basal lamina

Explanation:

The glomerular endothelial cells, the basal lamina (also known as Glomerular Basement Membrane) and the filtration slits between the podocytes carry out the filtration function of the glomerulus, separating the blood in the capillaries from the filtrate that forms in Bowman's capsule.

Basal lamina is also called basement membrane. It separates endothelial cells of blood vessel and epithelial cell of another tissue. It act as a molecular filter in kidney.