Glucagon's effect on cardiac performance includes which of the following?

Glucagon's effect on cardiac performance includes which of the following?

• A. Increases all: contractility, conduction speed, heart rate, and cardiac output
• B. Increases contractility only
• C. Increases heart rate only
• D. Decreases conduction speed

Answer: (A)

Glucagon’s effect on the heart comes from activating glucagon receptors in cardiac tissue, which raises intracellular cAMP through Gs protein signaling, bypassing beta-adrenergic receptors. This boost in cAMP increases calcium availability inside cardiac myocytes, producing a stronger heartbeat (positive inotropy). The same signaling also enhances automaticity of the SA node and speeds conduction through the AV node, leading to a faster heart rate (positive chronotropy) and quicker conduction (positive dromotropy). Together, these changes raise cardiac output, since both the force of contraction and the heart rate are increased. So the best description is that glucagon increases contractility, conduction speed, heart rate, and cardiac output. Statements claiming only one aspect or suggesting decreased conduction speed don’t fit, because glucagon acts on multiple facets of cardiac performance and speeds rather than slows conduction. This mechanism also explains its usefulness in situations like beta-blocker overdose, where glucagon can bypass blocked beta receptors to boost heart function.

Glucagon’s effect on the heart comes from activating glucagon receptors in cardiac tissue, which raises intracellular cAMP through Gs protein signaling, bypassing beta-adrenergic receptors. This boost in cAMP increases calcium availability inside cardiac myocytes, producing a stronger heartbeat (positive inotropy). The same signaling also enhances automaticity of the SA node and speeds conduction through the AV node, leading to a faster heart rate (positive chronotropy) and quicker conduction (positive dromotropy). Together, these changes raise cardiac output, since both the force of contraction and the heart rate are increased.

So the best description is that glucagon increases contractility, conduction speed, heart rate, and cardiac output. Statements claiming only one aspect or suggesting decreased conduction speed don’t fit, because glucagon acts on multiple facets of cardiac performance and speeds rather than slows conduction. This mechanism also explains its usefulness in situations like beta-blocker overdose, where glucagon can bypass blocked beta receptors to boost heart function.