What is tubular secretion? Name the substances secreted through the renal tubules.

Explanation

Tubular secretion refers to the addition of selected materials from the blood to the ultrafiltrate. The urine excreted contains both filtered and secreted substances. Once it enters the collecting duct, water is absorbed and concentrated hypertonic urine is formed. For every `H^(+)` secreted into the tubular filtrate, a `Na^(+)` is absorbed by the tubular cell. The `H^(+)` secreted combines with `HCO_(3)^(-) , HPO_(3)^(-)` and `NH_(3)^(-)` and gets fixed as `H2_CO_(4)^(+), H_2PO_(4)^(+)` and `NH_(4)^(+)` respectively. Since `H^(+)` gets fixed in the lluid, reabsorption of H+ is prevented.