True about the H+ secretion by the PCT is:
It is for acidification of urine
It occurs against the concentration gradient for H+
It is meant for reabsorption of the filtered bicarbonate
It is an example of diffusion trapping
(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 24meq/lit X 180L/day =4320meq/day 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 meq/day) In addition, PCT secretes 80meq/day of H+(: 4320 + 80 =4400meq/day) .This is net acid output.
Excretory System (Kidney, Bladder) Acid-Base Balance