Physiologists are investigating how the plasma concentration of various substances affects their excretion in the urine. In one experiment, a freely filtered substance at the glomerulus is infused intravenously at various rates. The substance's plasma concentration (mg/mL) and urinary excretion rate (mg/min) are measured. The following observations are made assuming a constant glomerular filtration rate (GFR) of 100 mL/min: Which of the following substances is most likely to demonstrate a similar pattern of filtration and excretion in a healthy adult?

Question

Physiologists are investigating how the plasma concentration of various substances affects their excretion in the urine. In one experiment, a freely filtered substance at the glomerulus is infused intravenously at various rates. The substance's plasma concentration (mg/mL) and urinary excretion rate (mg/min) are measured. The following observations are made assuming a constant glomerular filtration rate (GFR) of 100 mL/min:  Which of the following substances is most likely to demonstrate a similar pattern of filtration and excretion in a healthy adult?

Quizplus · Accepted Answer

Eductional Objective: Because normal plasma glucose concentrations are below the maximum tubular reabsorption ability, the renal tubules reabsorb the entire filtered load of glucose (transport maximum of glucose). When the filtered amount of glucose exceeds the transport maximum at higher plasma concentrations, it is excreted. The serum concentration at which glucosuria begins, known as the glucose threshold, is around 200 mg/dL.

Physiologists Are Investigating How the Plasma Concentration of Various Substances