Practice sessionHEALTHCARE & MEDICAL EXAMSMEDICAL LICENSING

USMLE (United States Medical Licensing Examination) Practice Exam 04

Practice exam for USMLE (United States Medical Licensing Examination).

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Question 1 of 300%

Time remaining180:00

Attempts allowedUnlimited

Difficulty mixE • M • H

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Question 1

MEDIUM

180:00

A 62-year-old man with long-standing hypertension is started on a medication that lowers blood pressure by increasing intracellular cyclic GMP in vascular smooth muscle. Which of the following best describes the immediate molecular effect responsible for vascular smooth muscle relaxation?

Increased cGMP (eg, via nitric oxide signaling) activates protein kinase G, which decreases intracellular Ca2+ and promotes activation of myosin light-chain phosphatase, resulting in dephosphorylation of myosin light chains and relaxation.

Key distractors: Phospholipase C inhibition is not the primary cGMP-mediated mechanism (B). Opening L-type Ca2+ channels would increase contraction (C).

Select one answer

Activation of myosin light-chain phosphatase leading to dephosphorylation of myosin light chains

Inhibition of phospholipase C leading to decreased inositol trisphosphate production

Opening of L-type calcium channels leading to increased intracellular calcium

Phosphorylation of myosin light chains by myosin light-chain kinase

Stimulation of Rho-kinase leading to increased calcium sensitivity of contractile proteins

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USMLE (United States Medical Licensing Examination) Practice Exam 04

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