A 57-Year-Old Man Comes to the Office for a Follow-Up

question 89

Multiple Choice

A 57-year-old man comes to the office for a follow-up appointment.  He has a history of systolic heart failure, which has been managed with appropriate medical therapy.  The patient experiences significant functional impairment at baseline and is able to walk only short distances.  His most recent echocardiogram revealed a left ventricular ejection fraction of 30% (normal ≥55%) .  The physician decides to add spironolactone to the treatment regimen.  The addition of this medication is most likely to cause a decrease in which of the following?

• A)Hydrogen ion generation by the proximal convoluted tubule
• B)Hydrogen ion secretion from the collecting duct
• C)Na⁺/K⁺/2Cl⁻ cotransport in the thick ascending limb
• D)Proximal convoluted tubule brush border transport capacity
• E)Urea reabsorption in the collecting duct

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Definitions:

Frequency-Dependent Selection

Natural selection in which a trait’s adaptive value depends on its frequency among members of a population.

Recessive Allele

An allele that produces its characteristic phenotype only when its paired allele is identical, often masked by a dominant allele in a heterozygote.

Dominant Allele

An allele that expresses its phenotype even in the presence of a recessive allele within a diploid organism.

Hardy-Weinberg Law

The Hardy-Weinberg Law is a principle that predicts the genetic variation and allele frequencies will remain constant in a population from generation to generation, assuming no evolutionary influences affect them.