Which of the following hormones is a positive inotropic agent?
Glucagon
Calcium channel blockers
Potassium
Beta blockers
The Correct Answer is A
A. Glucagon: Glucagon acts as a positive inotropic agent by increasing intracellular cyclic AMP (cAMP) in cardiac myocytes, which enhances calcium availability for actin-myosin cross-bridge formation. This results in stronger myocardial contractions and improved cardiac output. It is particularly used in cases of beta-blocker overdose to support cardiac contractility when adrenergic stimulation is blocked.
B. Calcium channel blockers: Calcium channel blockers, such as verapamil and diltiazem, inhibit calcium influx into cardiac and vascular smooth muscle cells. This action reduces myocardial contractility (negative inotropic effect) and slows conduction through the atrioventricular node, which can decrease cardiac output in some patients.
C. Potassium: Potassium primarily influences the resting membrane potential and excitability of cardiac cells. Hyperkalemia can depress myocardial contractility, whereas hypokalemia can predispose to arrhythmias. Potassium itself does not act as a positive inotropic agent.
D. Beta blockers: Beta-adrenergic blockers decrease sympathetic stimulation of the heart by antagonizing beta-1 receptors. This leads to reduced heart rate, decreased myocardial contractility (negative inotropic effect), and lower oxygen demand, making them useful for hypertension and heart failure management but not for increasing contractile force.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. It binds and stores oxygen for aerobic metabolism: Myoglobin is an oxygen-binding protein located within the cytoplasm of cardiac and skeletal muscle cells. It serves as an intracellular oxygen reservoir, facilitating rapid oxygen delivery to mitochondria during periods of high metabolic demand. This supports sustained aerobic metabolism and continuous ATP production necessary for cardiac contraction.
B. It transports glucose into heart cells: Glucose transport into cardiomyocytes is mediated by glucose transporters (GLUT1 and GLUT4), not by myoglobin. Myoglobin’s role is specifically related to oxygen handling, not nutrient transport.
C. It generates electrical impulses for contraction: Electrical impulses in the heart are generated by pacemaker cells in the sinoatrial node and conducted through the cardiac conduction system. Myoglobin has no role in depolarization or action potential propagation.
D. It breaks down fatty acids into ATP: Fatty acid oxidation occurs in mitochondria through beta-oxidation, producing ATP. Myoglobin does not catalyze this process; its primary function is oxygen storage and delivery to support mitochondrial metabolism.
Correct Answer is A
Explanation
Correct answer: Tachycardia
Tachycardia refers to a heart rate that exceeds the normal resting rate, typically defined as over 100 beats per minute in adults. It can originate from the atria, ventricles, or the sinoatrial (SA) node and may result from physiological responses such as exercise, stress, or fever, as well as pathological conditions including heart failure, anemia, or arrhythmias. Anatomically, tachycardia involves the conduction system of the heart including the SA node, atria, AV node, and ventricles, leading to faster depolarization and contraction.
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