Answer to Question #52670 in Biochemistry for Tapas

Question

Which one of the following components of urine in a healthy human DOES NOT differ much in concentration from that of blood plasma? And why?
a) NH4+ b) K+ c) Na+ d) SO42-

Answer 1

c) Na+
All four components are found in plasma and urine.
Concentration of NH4+ in urine is 1000 times bigger than in plasma. Great amounts of NH4+ ions are synthesised by glutaminase in renal cells. K+ ions are additionally secreted by renal cells to absorb sodium. This process is mediated by the work of K+/Na+-ATPase. Concentration of K+ ions in urine is 6-10 times bigger than one in plasma. Concentration of Na+ ions is almost the same in plasma and urine. Concentration of SO42- anions in urine is 100 times bigger than one in plasma due to its reduced reabsorption.
Of course concentration of these ions in blood plasma and urine depends on the diet.That's way concentration of these ions is determined in 24 hours urine.
Interesting that toxic ions (NH4+, SO42-, K+ in high concentrations) are excreted from the organism with high rate.