Given a constant urine flow rate, which graph accurately depicts the relationship between urine insulin concentration and time following a single injection of insulin into the bloodstream?
At any given instant, the distribution of insulin concentration across the bloodstream is relatively uniform. As a result, the elimination of insulin from the blood occurs at a consistent rate, resulting in an exponential decay when plotting blood concentration against time. Conversely, the plot of urine insulin concentration against time will exhibit the opposite trend. Hence, the correct answer is option 3.