How does tubular secretion help in maintaining ionic and acid-base balance in body-fluids?

Explanation

In addition to the role of Proximal Convoluted Tublues (PCT) in selective reabsorption of materials from the glomerular filitrate back into the blood of peritubular capillaries via the renal interstitium, they also alter the composition of filtrate by the process of secretion.
In its distal part, epithelial cells extract certain excretory substances from the blood of peritubular capillaries and secrete these into the filtrate.
Urea enters the filtrate via diffusion in the thin segment of ascending limb of Henle's loop.
Masimum hydrogen secretion occures in the proximal convoluted tubules. Removel of hydrogen ion and `NH_(3)` from the blood in the PCT and Distal Convoluted Tubule (DCT) helps in maintaining pH of the blood , i.e., between 6 to 8.
Tubular secretion although possess a minor role in functioning of the human kidney, but plays an essential role in animals like marine fishes and desert amphibians, because these animal do not possess well developed glomeruli hence their urine is mainly formed by the tubular secretion of urea, creatinine and mineral ions.