On cardiology service rounds, your team sees a patient admitted with an acute congestive heart failure exacerbation. In congestive heart failure, decreased cardiac function leads to decreased renal perfusion, which eventually leads to excess volume retention. To test your knowledge of physiology, your attending asks you which segment of the nephron is responsible for the majority of water absorption. Which of the following is a correct pairing of the segment of the nephron that reabsorbs the majority of all filtered water with the means by which that segment absorbs water?
ADistal convoluted tubule via passive diffusion following ion reabsorption
BDistal convoluted tubule via aquaporin channels
CThick ascending loop of Henle via passive diffusion following ion reabsorption
DProximal convoluted tubule via passive diffusion following ion reabsorption
ECollecting duct via aquaporin channels
A scientist is studying the excretion of a novel toxin X by the kidney in order to understand the dynamics of this new substance. He discovers that this new toxin X has a clearance that is half that of inulin in a particular patient. This patient's filtration fraction is 20% and his para-aminohippuric acid (PAH) dynamics are as follows: Urine volume: 100 mL/min Urine PAH concentration: 30 mg/mL Plasma PAH concentration: 5 mg/mL Given these findings, what is the clearance of the novel toxin X?
A1,500 mL/min
B600 mL/min
C300 mL/min
D60 mL/min
E120 mL/min
During a clinical study evaluating the effects of exercise on muscle perfusion, 15 healthy individuals perform a 20-minute treadmill run at submaximal effort. Before and after the treadmill session, perfusion of the quadriceps muscle is evaluated with contrast-enhanced magnetic resonance imaging. The study shows a significant increase in muscle blood flow per unit of tissue mass. Which of the following local changes is most likely involved in the observed change in perfusion?
AIncrease in adenosine
BDecrease in potassium
CIncrease in thromboxane A2
DIncrease in endothelin
EDecrease in prostacyclin
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