Short notes on active secretion
While tubular reabsorbtion removes the necessary substances from the filterate into the blood, secretion removes materials from the blood and adds to the filterate. Metabolic products present in the blood but not required by the body and in fact are injurious or secreted out from the blood to the filterate.
The tubular epithelium plays an important role in this. The substances that are secreted into the filterate include potassium, hydrogen, ammonia, creatine, uricacid and drugs like pencillin. These secretions mix with the filterate of the nephrons and constitute the urine. Tubular secretion has two main roles – it rids the body of unwanted materials and it also controls the pH of the blood.