Electrolytes and

Renal Function

Kidney – regulation & conservation of electrolytes

1. Glomerulus- acts as filter, retaining large proteins, and protein bound constituents

2. Renal Tubules – *Phosphate reabsorption is inhibited by PTH,

excretion of Phosphate is stimulated by calcitonin

*Calcium is reabsorbed by the influence of PTH and 1,25-dihydroxycholecalciferol . Calcitonin stimulates excretion of calcium

*Magnesium reabsorption occurs largely in thick ascending limb of loop of Henle.

*Sodium reabsorption can occur through three mechanism:

Approx. 70% of Na in the filtrate is reabsorbed in the PCT by iso-osmotic reabsorption. It is limited, however, by the availability of Cl to maintain electrically neutrality.

Na is reabsorbed in exchange of H. This

reaction is linked with HCO3 and depends on carbonic anhydrase.

Na is reabsorbed stimulated by aldosterone in exchange of K in DCT

Cl is reabsorbed in part, by passive transport in the PCT along the conc. Gradient created by Na

K is reabsorbed by two mechanism:◦ Active reabsorption in in the PCT almost

completely conserves K◦ Exchange with Na is stimulated by aldosterone. H

competes with K for this exchange

Bicarbonate is recovered from the glomerulus filtrate and converted to CO2 when H is excreted in the urine.

Loop of Henle:◦ With normal AVP function, it creates an osmotic

gradient that enables water reabsorption to be increased or decreased in response to body fluid changes in osmolality

Collecting Ducts:Also under AVP influence, this is where final

adjustment of water excretion is made.