What is glomerular filtrate?

Glomerular filtrate, also known as primary urine, is the fluid produced by the process of ultrafiltration in the kidney. It is formed when high blood pressure forces blood plasma—minus its macromolecules like proteins—out of the glomerulus and into the Bowman’s capsule.123

This filtrate contains water and various crystalloids, including nitrogenous compounds, glucose, and salts, which are filtered nonselectively based on size. Because the glomerular membrane restricts the passage of large molecules, the resulting filtrate is essentially a protein-free solution of blood plasma.412

Once formed, the glomerular filtrate enters the nephron tubule, where the majority of its water and essential substances are reabsorbed into the blood, while waste products are concentrated to eventually form urine.125