Name one substance or blood component that can't enter the kidney tubuel and why?

Red blood cells cannot enter the kidney tubule because they are too large to pass through the filtration barrier of the glomerulus. The glomerulus only allows small molecules and ions to pass through, while larger molecules like red blood cells are filtered out and remain in the bloodstream.

Red blood cells cannot enter the kidney tubule because they are too large to pass through the glomerular filter and into the Bowman's capsule.