Which statement best explains why blood cells are NOT found in the urine of a healthy person?

The correct option is: They are too large to pass through glomerular pores

To understand why blood cells are not found in the urine of a healthy individual, we need to look at the filtration process in the kidneys. The functional unit of the kidney is the nephron, which begins with a filtering unit called the renal corpuscle. This corpuscle contains a network of capillaries called the glomerulus, surrounded by Bowman's capsule.

During urine formation, blood enters the glomerulus under high pressure. The walls of the glomerular capillaries contain tiny pores (fenestrations) that act as a physical sieve or filter. This filtration barrier allows water, ions, glucose, amino acids, and small waste molecules (like urea) to pass through into Bowman's space, forming the glomerular filtrate.

However, large structures present in the blood, such as red blood cells, white blood cells, platelets, and large plasma proteins (like albumin), are physically too large to pass through these narrow glomerular pores. As a result, they remain within the bloodstream and continue circulating in the body, rather than entering the nephron tubules to be excreted. Therefore, the absence of blood cells in the urine of a healthy person is due to their size preventing them from passing through the glomerular filtration barrier.