WBR0799

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::A researcher is studying the consumption of energy by brain cells in rats. In his experiment, he observes that during an overnight fast, glucose is extracted from the blood vessels and brain cells consume only glucose. In converse, during prolonged starvation the researcher observes that the consumption of another compound X by the brain cells increases, as shown in the image below. Which of the following compounds most likely corresponds to compound X? ]]
Answer A	AnswerA::Beta-hydroxybutyrate
Answer A Explanation	AnswerAExp::Beta-hydroxybutyrate is a ketone body that is used by the brain during prolonged starvation.
Answer B	AnswerB::Histidine
Answer B Explanation	AnswerBExp::Histidine is not a ketone body. It is not the primary source of fuel for the brain during starvation.
Answer C	AnswerC::Alpha-ketoglutarate
Answer C Explanation	AnswerCExp::Alpha-ketoglutarate is not a ketone body. It is not the primary source of fuel for the brain during starvation.
Answer D	AnswerD::Ornithine
Answer D Explanation	AnswerDExp::Ornithine is not a ketone body. It is not the primary source of fuel for the brain during starvation.
Answer E	AnswerE::Fructose
Answer E Explanation	AnswerEExp::Fructose is not a ketone body. It is not the primary source of fuel for the brain during starvation.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The researcher's experiment shows that upon starvation of rats, their brain cells stop consuming glucose and consume ketone bodies instead. There are 2 main ketone bodies: Beta-hydroxybuturate and acetoacetate. As such, compound X most likely corresponds to any of the 2 compounds. After an overnight fast in physiologic conditions, glucose is the only consumed compound by the brain. However, following starvation glucose only represents less than 1/3 of the consumed compounds. The brain's capacity to extract ketone bodies rises; these bodies become the main supply of nutrition to brain cells in such moments of stress. Educational Objective: Beta-hydroxybutyrate and acetoacetate are ketone bodies that are consumed by the brain in prolonged starvation. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::ketone, WBRKeyword::body, WBRKeyword::acetone, WBRKeyword::beta-hydroxybutyrate, WBRKeyword::acetoacetate, WBRKeyword::bodies, WBRKeyword::brain, WBRKeyword::cell, WBRKeyword::cells, WBRKeyword::fuel, WBRKeyword::source, WBRKeyword::energy, WBRKeyword::glucose, WBRKeyword::extraction, WBRKeyword::consumption, WBRKeyword::experiment
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Order in Linked Questions	LinkedOrder::