Glomerular Filtration Barrier: Preventing Protein Loss in the Nephron

Size-selective filtration is the major mechanism responsible for preventing filtration of proteins in nephron.

The glomerular filtration barrier, which consists of the fenestrated endothelium of the glomerular capillaries, the glomerular basement membrane, and the podocytes of the visceral epithelium, acts as a molecular sieve, allowing the filtration of small molecules such as water, electrolytes, and small organic molecules, while restricting the passage of larger molecules such as proteins.

The size selectivity of the glomerular filtration barrier is primarily determined by the size and charge of the molecules. Smaller molecules, such as water and electrolytes, can easily pass through the pores of the filtration barrier, while larger molecules, such as proteins, are largely retained.

In addition to size-selective filtration, charge-selective filtration also plays a role in preventing the filtration of proteins. The glomerular filtration barrier is negatively charged, which repels negatively charged molecules, such as proteins, and attracts positively charged molecules.

The combined effects of size-selective and charge-selective filtration ensure that only small, uncharged molecules are filtered into the Bowman's capsule, while larger molecules, including proteins, are mostly retained in the blood.