What are the main processes of urine formation?

The main processes of urine formation are: Glomerular Filtration, Reabsorption and tubular secretion.

Glomerular filtration removes solutes from the blood which is the first step of urine formation. The force of hydrostatic pressure in the glomerulus is the driving force that pushes the filtrate out of the capillaries.

Tubular reabsorption is the process by which the nephron removes water and reabsorbs solutes from the tubular fluid and returns them to the blood. Reabsorption of water also occurs passively in the initial segments of the nephron. For example, substances like glucose, amino acids, etc., are reabsorbed actively whereas the nitrogenous wastes are absorbed by passive transport in the tubules.

Tubular secretion occurs in the proximal convoluted tubule of the nephron and is responsible for the transport of specific molecules out of the blood and then into the urine. It helps in the maintenance of ionic and acid base balance of body fluids.