Question
Which one of the following components of urine in a healthy human does not differ much in concentration from that of blood plasma?
NH4 +
K+
Na+
SO4 2-
Solution
D.
SO4 2-
SO4 2-, creatinine and other metabolic end products are the non-threshold substances which are not at all reabsorbed and are excreted in urine even under normal conditions. This is the reason these substances do not differ much in concentration from that of blood plasma.
Na+, K+, glucose and Ca2+ are the high-threshold substances, which are reabsorbed very extensively and do not appear in urine under normal conditions. These appear in urine only if their concentration in plasma is abnormally high or in renal diseases when reabsorption is affected. NH4 + is excreted in the form of urea.
