Mention the two main processes in urine formation.

The two main processes in urine formation are:

1. Ultrafiltration — In the glomerulus the blood is filtered under pressure, so that water, mineral salts, glucose, amino acids and nitrogenous wastes pass into the Bowman's capsule while blood cells and large molecules like proteins are retained.
2. Selective reabsorption — As the filtrate passes along the renal tubule, useful materials such as most of the water, all the glucose and amino acids and some mineral salts are taken back into the surrounding blood capillaries.