The high threshold substances are

Proximal and distal convoluted tubules are parts of a

Choose the mismatched part of the nephron with its function.

$A :$ Tubular secretion is of considerable importance in marine teleost fishes.
$R :$ These have aglomerular kidney,$i.e.$,no filtration occurs and tubular secretion is the only way of excretion.

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

The part of the nephron involved in the active reabsorption of sodium is