Which type of substances are typically unable to pass through the glomerulus during filtration?

The glomerulus functions as a filtration barrier in the kidneys, selectively allowing certain substances to pass while preventing others from entering the filtrate. Red blood cells and proteins are typically unable to pass through this barrier due to their size and charge.

Red blood cells are significantly larger than the filtration pores of the glomerulus, which are designed to restrict the passage of large molecules and cells. Proteins, especially large ones such as albumin, are also too large to be filtered under normal circumstances. The presence of these substances in the urine typically indicates a malfunction in the filtration process, such as in conditions like glomerulonephritis or nephrotic syndrome.

In contrast, substances like water, electrolytes, glucose, and amino acids are usually small enough to pass through the glomerular membrane into the filtrate. This selective permeability is crucial for maintaining the body’s homeostasis, allowing the kidneys to reabsorb essential nutrients and maintain fluid balance.