Urine formation occurs during 3 processes:

1.Secretion: Fluid from a number of nephrons moves from the distal tubules to a common collecting duct which carries what can now be called urine to the renal pelvis.In the loope of Henle, the descending part responsible for the reabsorption of water, while the ascending part reabsorb Na* and Cl.

In the distal tubules, active transport is used to pull hydrogen ions, creatinine, and drugs such as penicillin out of the blood and into the filtrate.2.3.