WBR0420

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A researcher is studying the fate of bile salts following secretion into the gastrointestinal tract. At the level of the kidney, the researcher notes that the concentration of bile salts within the nephron increases sharply as concentrations are measured in various segments of the nephron. According to the image below, which of the following nephron segments is responsible for the secretion of bile salts? ]]
Answer A	AnswerA::A
Answer A Explanation	AnswerAExp::The proximal tubule of the nephron is the most important segment for secretion of bile salts.
Answer B	AnswerB::B
Answer B Explanation	[[AnswerBExp::Thin descending segment of loop of Henle is not the major site of bile salt secretion. The thin descending loop of Henle has thin epithelial membranes that lacks brush borders. Because it is considered a segment with minimal metabolic activity, few mitochondria are located in this site of nephron.]]
Answer C	AnswerC::C
Answer C Explanation	[[AnswerCExp::Thick ascending loop of Henle is not the major site of bile salt secretion. It has thick epithelial cells with high metabolic activity. Reabsorption of major ions, such as sodium, potassium, and chloride, occurs at the level of thick ascending loop of Henle.]]
Answer D	AnswerD::D
Answer D Explanation	[[AnswerDExp::The distal tubule is not the major site of bile salt secretion. Its first part forms the macula densa, a part of the juxtaglomerular complex. The convoluted part of the distal tubules has reabsorptive capacity similar to that of the thick ascending loop of Henle. The distal part of the distal tubules has similar functional characteristics as that of cortical collecting tubule.]]
Answer E	AnswerE::E
Answer E Explanation	AnswerEExp::The collecting duct is not the major site of bile salt secretion. Collecting tubules contain principal cells and intercalated cells.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The proximal tubule is the most important nephron segment responsible for secretion of organic acids and bases. As such, bile salts, oxalate, urate, and catecholamines are all secreted mainly in the proximal tubule. Both filtration and secretion of these compounds play an important role in their renal excretion. The proximal tubule is considered a site of major metabolic activity with numerous mitochondria to serve its metabolic function. Educational Objective: The proximal tubule of the nephron is the most important segment for secretion of bile salts, oxalate, urate, and catecholamines. Educational Objective: References: ]]
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