Identify and describe the three major processes involved in urine formation.

Glomerular filtration is a nonselective, passive process with the glomerulus acting as the filter. The filtrate formed is essentially blood plasma without blood proteins, which are too large to pass through the filtration membrane into the renal tubule. Tubular reabsorption is the process by which the body reclaims substances within the filtrate that it wants to keep. Most reabsorption is an active process using membrane carriers. Substances that are typically reabsorbed include amino acids, glucose, and ions. Most reabsorption occurs in the proximal convoluted tubules. Tubular secretion is the opposite process. With secretion, substances such as hydrogen ions, potassium ions, and creatinine are removed from the peritubular capillaries into the tubules to be eliminated in urine.