An antibiotic is circulating through the blood when it passes through the kidneys. Only a miniscule amount of it passes through the glomerular capillary and enters the glomerular filtrate, but when its presence in the urine is measured, it has been almost completely excreted! How is this possible?
A. During the process of reabsorption, flow of water across the tubular membrane into the peritubular capillary passively encourages the antibiotic to cross the opposite way.
B. Sodium ions crossing into the blood of the peritubular capillary increases osmotic pressure and forces the antibiotic into the proximal tubule.
C. The antibiotic is actively transported into the proximal tubule during tubular secretion.
D. Stimulation from nerves causes the efferent arteriole to constrict and force the antibiotic through the glomerular capillary into the filtrate.
Answer: C
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