WBR0387

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A researcher is studying the role of aldosterone at the level of renal tubules. He conducts an experiment whereby he measures urinary concentration of sodium, potassium, and hydrogen immediately prior and following aldosterone administration. With respect to urinary concentrations prior to the administration of aldosterone, which of the following parameters is true for the urinary concentrations of sodium, potassium, and hydrogen following aldosterone administration? ]]
Answer A	AnswerA::A
Answer A Explanation	AnswerAExp::An increase in the concentration of sodium, accompanied by a decrease in the concentration of potassium and hydrogen, occurs in the serum, not in urine.
Answer B	AnswerB::B
Answer B Explanation	[[AnswerBExp::Following aldosterone administration, the urinary concentration of sodium is decreased due to the reabsorption of sodium. On the other hand, the urinary concentration of hydrogen is increased due to the excretion of hydrogen.]]
Answer C	AnswerC::C
Answer C Explanation	[[AnswerCExp::Aldosterone accelerates the ion exchange of sodium for potassium or hydrogen. It increases the reabsorption of sodium and the excretion of both potassium and hydrogen.]]
Answer D	AnswerD::D
Answer D Explanation	[[AnswerDExp::Following aldosterone administration, hydrogen is excreted into the urine, and urinary concentration of hydrogen is expected to increase.]]
Answer E	AnswerE::E
Answer E Explanation	[[AnswerEExp::Following aldosterone administration, the urinary concentration of potassium increases whereas the serum concentration of potassium decreases due to aldosterone-mediated urinary excretion of potassium.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Aldosterone accelerates the ion exchange of sodium for potassium and hydrogen. Aldosterone acts at the level of the collecting ducts to reabsorb sodium and excrete potassium and hydrogen. Thus, urinary concentrations of sodium will decrease, while urinary concentrations of potassium and hydrogen will increase. Educational Objective: Aldosterone acts at the level of the renal collecting tubule. It accelerates the ion exchange of sodium (reabsorption) for potassium or hydrogen (excretion). Administration of aldosterone results in a decrease in the urinary concentration of sodium and an increase in the urinary concentration of potassium and hydrogen. References: First Aid 2014 page 318, 528, 530]]
Approved	Approved::Yes
Keyword	WBRKeyword::Aldosterone, WBRKeyword::Sodium, WBRKeyword::Potassium, WBRKeyword::Hydrogen, WBRKeyword::Reabsorption, WBRKeyword::Urinary concentration, WBRKeyword::Excretion, WBRKeyword::Collecting tubule
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::