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Which of the following hormones is a positive inotropic agent?

A.

Glucagon

B.

Calcium channel blockers

C.

Potassium

D.

Beta blockers

Answer and Explanation

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.


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Related Questions

Correct Answer is {"dropdown-group-1":"B"}

Explanation

A. P: The P wave represents atrial depolarization. It reflects the electrical activity as the impulse spreads from the sinoatrial (SA) node across the atrial myocardium, causing atrial contraction. Because the atria are smaller than the ventricles, the electrical signal is smaller in amplitude.

B. QRS: The QRS complex represents ventricular depolarization. It corresponds to the rapid spread of electrical impulses through the ventricles via the bundle branches and Purkinje fibers, leading to ventricular contraction. Since the ventricles have significantly greater muscle mass than the atria, this depolarization produces a larger and stronger electrical signal on the ECG.

C. T: The T wave represents ventricular repolarization, the process by which ventricular muscle cells return to their resting membrane potential after contraction. It does not represent depolarization.

D. PR: The PR interval reflects the time required for the electrical impulse to travel from the atria through the atrioventricular (AV) node to the ventricles. It represents conduction delay, not ventricular depolarization itself.

Correct Answer is {"dropdown-group-1":"A","dropdown-group-2":"B","dropdown-group-3":"C"}

Explanation

Correct answer:

  • J: Pulmonary veins
  • G: Right ventricle
  • D: Pulmonary trunk

J: Pulmonary veins- Pulmonary veins are blood vessels that carry oxygenated blood from the lungs to the left atrium of the heart. Normally, there are four pulmonary veins—two from each lung. They enter the posterior aspect of the left atrium and play a vital role in systemic circulation by delivering oxygenated blood for distribution throughout the body.

G: Right ventricle- The right ventricle is the lower right chamber of the heart responsible for pumping deoxygenated blood to the lungs for oxygenation. It receives blood from the right atrium through the tricuspid valve and ejects it into the pulmonary artery via the pulmonary valve. It generates enough pressure to move blood through the pulmonary arteries to the lungs, where carbon dioxide is exchanged for oxygen.

D: Pulmonary trunk- The pulmonary trunk is a large artery that carries deoxygenated blood from the right ventricle to the lungs. It begins at the pulmonary valve and extends upward before dividing into the right and left pulmonary arteries. It is located anterior to the ascending aorta and it transports blood to the lungs for gas exchange.

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