What happens during filtration in the kidney glomerulus?

Glomerular filtration is the process by which blood plasma is ultrafiltered from the glomerulus into the Bowman’s capsule to begin urine formation. This process is driven by blood pressure within the glomerular capillaries, which is significantly higher than in other capillaries in the body.123

The filtration barrier consists of three layers:
* Endothelial cells: The inner layer, which contains numerous pores called fenestrae.1
* Basement membrane: A continuous layer of hydrated collagen and glycopeptides that acts as a primary restriction point. It is negatively charged, which helps repel anionic macromolecules like albumin, while size-based restriction prevents larger proteins from passing through.1
* Podocytes: The external layer of epithelial cells with slender extensions called pedicels, which create slitlike spaces closed by a fine slit diaphragm.1

Through simple diffusion and bulk flow, water and crystalloids pass into the capsular space, while blood cells and large proteins are typically excluded. In the context of renal system disease, damage to the glomerulus can increase its permeability, leading to proteinuria and potentially nephrotic syndrome.14