WBR0977

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Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biochemistry
Sub Category SubCategory::General Principles
Prompt [[Prompt::A scientist studies the expression and enzymatic activities of aldose reductase and sorbitol dehydrogenase using western blotting and immunohistochemistry techniques. The study is conducted on samples of human cells obtained from multiple organs. In one sample, the expression of only aldose reductase is positive, whereas the expression of sorbitol dehydrogenase is completely absent. The sample is most likely obtained from which of the following organs?]]
Answer A AnswerA::Liver
Answer A Explanation [[AnswerAExp::Sorbitol dehydrogenase is present in the liver.]]
Answer B AnswerB::Retina
Answer B Explanation [[AnswerBExp::Sorbitol dehydrogenase is absent in the retina. The obtained sample of cells lacking sorbitol dehydrogenase in the study is likely derived from the retina.]]
Answer C AnswerC::Ovaries
Answer C Explanation [[AnswerCExp::Sorbitol dehydrogenase is present in the ovaries.]]
Answer D AnswerD::Seminal vesicles
Answer D Explanation [[AnswerDExp::Sorbitol dehydrogenase is present in the seminal vesicles.]]
Answer E AnswerE::Lens
Answer E Explanation [[AnswerEExp::Sorbitol dehydrogenase is present in the lens albeit in low concentrations.]]
Right Answer RightAnswer::B
Explanation [[Explanation::The sorbitol pathway involves 2 major reactions that result in production of fructose. Glucose is converted to sorbitol by the action of aldose reductase; then sorbitol is converted to fructose by the action of sorbitol dehydrogenase. Sorbitol dehydrogenase is present in the seminal vesicles, ovaries, liver, and the lens. In contrast, it is absent in the retina, Schwann cells, and the kidneys. Therefore, when glucose concentration is chronically elevated (e.g. individuals with long-standing uncontrolled diabetes mellitus), glucose is continuously converted to fructose. In organs that lack sorbitol dehydrogenase, accumulation of sorbitol results in osmotic damage and target organ complications (cataract, retinopathy, and neuropathy among diabetic individuals).

Shown below is a figure that illustrates sorbitol metabolism

Educational Objective: Sorbitol dehydrogenase is present in the seminal vesicles, ovaries, and liver. It is absent in the retina, Schwann cells, and the kidneys.
References: First Aid 2014 page 107]]

Approved Approved::Yes
Keyword WBRKeyword::Sorbitol, WBRKeyword::Sorbitol dehydrogenase, WBRKeyword::Lens, WBRKeyword::Retina, WBRKeyword::Liver, WBRKeyword::Ovaries, WBRKeyword::Seminal vesicles, WBRKeyword::Retina, WBRKeyword::Kidneys, WBRKeyword::Aldose reductase, WBRKeyword::Osmotic damage, WBRKeyword::Diabetes mellitus, WBRKeyword::Glucose, WBRKeyword::Sorbitol pathway
Linked Question Linked::
Order in Linked Questions LinkedOrder::