WBR0738

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Endocrine, SubCategory::Renal
Prompt	[[Prompt::A researcher is studying the effect of a new medication, MedX. He uses mice to conduct his experiments. Following the intravenous administration of MedX, the researcher notes the decreased secretion of aldosterone secondary to MedX's effect in reducing the production of a compound from the pulmonary vasculature. Based on the image below, which of the following reactions is most likely the first to be inhibited upon administration of MedX? ]]
Answer A	AnswerA::A
Answer A Explanation	AnswerAExp::Angiotensinogen is formed by the liver. It is converted to angiotensin I by renin. Renin is synthesized and stored in the juxtraglomerular apparatus of the kidney.
Answer B	AnswerB::B
Answer B Explanation	AnswerBExp::Angiotensin-converting enzyme (ACE) is synthesized in various cells, including the endothelial cells of the pulmonary vasculature. ACE converts angiotensin I to angiotensin II.
Answer C	AnswerC::C
Answer C Explanation	AnswerCExp::ACE does not act at this level of the pathway.
Answer D	AnswerD::D
Answer D Explanation	AnswerDExp::ACE does not act at this level of the pathway.
Answer E	AnswerE::E
Answer E Explanation	AnswerEExp::ACE does not act at this level of the pathway.
Right Answer	RightAnswer::B
Explanation	[[Explanation::The renin-angiotensin aldosterone system (RAAS) is a major hormonal pathway that plays a significant role in the control of arterial blood pressure, tissue perfusion, and extracellular volume. The RAAS pathway begins by the expression and secretion of renin, the rate-limiting processing enzyme that is synthesized as a preprohormone. Renin is mainly synthesized and stored in the juxtraglomerular (JG) apparatus, composed of JG cells and macula densa. The JG apparatus lines the afferent arteriole of the renal glomerulus. Renin cleaves the N-terminal portion of angiotensinogen, a compound that is mainly expressed by the liver at a stable rate. Angiotensinogen cleavage results in the formation of angiotensin I, a biologically inert decapeptide. Angiotensin I is hydrolyzed by angiotensin-converting enzyme (ACE) or kininase II, an enzyme on plasma membranes of endothelial cells, neuroepithelial cells, and renal proximal tubule cells. ACE acts by removing the C-terminal dipeptide to form angiotensin II, an octapeptide. Also, ACE has a role in metabolizing bradykinin and kallidin, which are important vasodilator peptides. Unlike angiotensin I, angiotensin II is an active potent vasoconstrictor. Angiotensin II is the primary effector of numerous actions. The effects of MedX are similar to angiotensin-converting enzyme (ACE) inhibitors. ACE is synthesized in various cells, including the endothelial cells of the pulmonary vasculature. ACE converts angiotensin I to angiotensin II. The inhibition of the ACE leads to the inhibition of the entire renin-angiotensin pathway and the deficient production of aldosterone. Educational Objective: Angiotensin-converting enzyme (ACE) is synthesized in various cells, including the endothelial cells of the pulmonary vasculature. ACE converts angiotensin I to angiotensin II. References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Angiotensin, WBRKeyword::Converting, WBRKeyword::Enzyme, WBRKeyword::ACE, WBRKeyword::Inhibitor, WBRKeyword::ACE inhibitor, WBRKeyword::Angiotensinogen, WBRKeyword::Renin, WBRKeyword::Pulmonary, WBRKeyword::Vasculature, WBRKeyword::Hormone, WBRKeyword::Conversion, WBRKeyword::Angiotensin I, WBRKeyword::Angiotensin II, WBRKeyword::Angiotensin 1, WBRKeyword::Angiotensin 2, WBRKeyword::Aldosterone
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