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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{Rim}} (Reviewed by  {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A scientist studies the expression and enzymatic activities of aldose reductase and sorbitol dehydrogenase by western blotting and immunohistochemistry.   The study was conducted on different samples of rat cells derived from different organs. In one of the samples, the expression of only aldose reductase was positive, whereas sorbitol dehydrogenase was absent. From which of the following organs does this sample of cells most likely derive from?
|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/tissues?
|Explanation=[[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 lens; however, it is absent in retina, schwann cells and kidneys. Therefore, when glucose levels is chronically elevated, as seen in the case of poorly controlled [[diabetes]], [[glucose]] gets converted to sorbitol leading to osmotic damage in cells lacking sorbitol dehydrogenease.  The complications of this osmotic damage include [[retinopathy]] and [[nephropathy]] that occur in diabetics. Shown below is a diagram depicting sorbitol metabolism.
|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).<br>
 
Shown below is a figure that illustrates sorbitol metabolism<br>
[[ File:Sorbitol pathway.png]]
[[Image:Sorbitol pathway illustration.png|700px]]
 
'''Educational objective:'''
Sorbitol dehydrogenase is present in the seminal vesicles, ovaries, liver and lens; however, it is absent in the retina, schwann cells and kidneys.
 
'''Reference:'''
First aid for USMLE step 1, 2013. Page 105.
|AnswerA=Liver
|AnswerA=Liver
|AnswerAExp=Sorbitol dehydrogenase is present in the [[liver]].
|AnswerAExp=Sorbitol dehydrogenase is present in the [[liver]].
|AnswerB=Retina
|AnswerB=Retina
|AnswerBExp=Sorbitol dehydrogenase is absent in the [[retina]]. Thus, the sample of cells lacking sorbitol dehydrogenase in the experiment is likely derived from the retina.
|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.
|AnswerC=Ovaries
|AnswerC=Ovaries
|AnswerCExp=Sorbitol dehydrogenase is present in the [[ovaries]].
|AnswerCExp=Sorbitol dehydrogenase is present in the [[ovaries]].
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|AnswerDExp=Sorbitol dehydrogenase is present in the [[seminal vesicle]]s.
|AnswerDExp=Sorbitol dehydrogenase is present in the [[seminal vesicle]]s.
|AnswerE=Lens
|AnswerE=Lens
|AnswerEExp=Sorbitol dehydrogenase is present in the [[lens]].
|AnswerEExp=Sorbitol dehydrogenase is present in the [[lens]] albeit in low concentrations.
|EducationalObjectives=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
|RightAnswer=B
|RightAnswer=B
|Approved=No
|WBRKeyword=Sorbitol, Sorbitol dehydrogenase, Lens, Retina, Liver, Ovaries, Seminal vesicles, Retina, Kidneys, Aldose reductase, Osmotic damage, Diabetes mellitus, Glucose, Sorbitol pathway,
|Approved=Yes
}}
}}

Latest revision as of 02:15, 28 October 2020
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/tissues?]]
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
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