<prompt> True about the H secretion by the PCT is:It is for acidification of urineIt occurs against the concentration gradient for HIt is meant for reabsorption of the filtered bicarbonateIt is an example of diffusion trapping  <response>: C It is meant for reabsorption of filtered bicarbonate A Acidification of urine is done by collecting ducts. H secretion in PCT occurs along the concentration gradient. In collecting ducts H secretion is against concentration gradient Diffusion trapping occurs in collecting ducts not in PCT. H secretion in PCT is meant for reabsorption of bicarbonate. Amount of filtered is calculated by per unit time Px x GFRPx plasma concentration of substance. How much bicarbonate is filtered per unit time is 24meqlit X 180Lday 4320meqday Most of this is reabsorbed in PCT HCO3- is ionic. Ionic substances are less diffusible. So, first it is conveed to non-ionic form. For this H is secreted by PCT. H is secreted in equal amounts of HCO3- i.e 4320 meqday In addition, PCT secretes 80meqday of H: 4320 80 4400meqday .This is net acid output. 