Are blood cells and most proteins too large to enter Bowman's capsule?

Yes, blood cells and most proteins are typically too large to enter Bowman's capsule. The filtration barrier in the kidneys, consisting of endothelial cells, basement membrane, and podocytes, selectively permits the passage of smaller molecules like water, electrolytes, and small solutes while restricting larger substances. This size-selective filtration helps maintain the composition of the blood and prevent the loss of critical proteins and cells during urine formation.