Network to tubes found in a nephron. It consists of the proximal convoluted tubule, the loop of Henle, the distal tubule, and the collecting tubule. The reabsorption and secretion stages of urine production occur within the renal tubule. As the glomerular filtrate passes through the renal tubule, most of the water and some of the dissolved substances, such as amino acids and electrolytes, are reabsorbed. At the same time, substances that are too large to filter into Bowman's capsule, such as urea, are secreted directly from the blood stream into the renal tubule. The filtrate that reaches the collecting tubule becomes urine.