RLO: The Physiology of the Kidneys


Tubule Secretion

Some substances aren't filtered via the Bowman’s capsule but enter the nephron further down in the proximal or distal convoluted tubules. This occurs in a process called tubule secretion.

Some drug metabolites are secreted into the tubule in this manner from the blood stream. In addition, metabolites produced by the cells forming the tubules themselves often enter the nephron in this way.

For example, hydrogen, bicarbonate and ammonium ions, products of tubule cell metabolism, are secreted into the lumen of the renal tubule. These processes are important in the regulation of the acid-base balance of the body. It is because of this that urine pH can dramatically vary from being either acidic or alkaline.