How does the glomerulus filter materials from the blood?

The glomerulus filters blood through a process of ultrafiltration driven by high blood pressure within its capillaries. This pressure, typically around 45 mmHg, forces plasma out of the capillaries and into the Bowman’s capsule, while retaining larger components like macromolecules and blood cells.1234

The filtration barrier consists of three layers that regulate what passes into the nephron:

• Endothelium: The inner layer of the capillary wall, which contains numerous pores called fenestrae.2
• Basement membrane: A hydrated gel layer of collagen and glycopeptides that acts as a primary filter. It restricts molecules based on size and negative electrostatic charge, effectively blocking anionic proteins like albumin.2
• Podocytes: The external layer composed of epithelial cells with foot processes (pedicels). These create slitlike spaces closed by a fine diaphragm, providing a final barrier to large molecules.2

Through these layers, substances in true solution (crystalloids) pass into the capsular space as filtrate, while colloids such as proteins are held back.2