Which combination of substances increases heart rate as listed?

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Multiple Choice

Which combination of substances increases heart rate as listed?

Heart rate rises when the heart’s sympathetic drive increases and when hormonal signals boost the heart’s responsiveness over time. Epinephrine and norepinephrine are the classic fast-acting drivers: they bind to beta-1 receptors in the SA node, quickening the rate of diastolic depolarization, which directly speeds up heart rate and also boosts contractility. Thyroid hormone (T3) works on a slower timeline but sustains and amplifies this effect by increasing the expression of beta-adrenergic receptors and pacemaker channels, making the heart more responsive to catecholamines and capable of beating faster even at rest or with modest activity. Put together, these substances produce both immediate and lasting increases in heart rate. The other options don’t produce the same clear, sustained increase. Acetylcholine acts on parasympathetic receptors to slow the heart. Cortisol can enhance sympathetic effects but is not a direct, rapid driver of heart rate in the same way catecholamines are. Insulin and glucagon don’t directly set the pace of the heart like that combination, and dopamine’s effect is more variable depending on dose.

Heart rate rises when the heart’s sympathetic drive increases and when hormonal signals boost the heart’s responsiveness over time. Epinephrine and norepinephrine are the classic fast-acting drivers: they bind to beta-1 receptors in the SA node, quickening the rate of diastolic depolarization, which directly speeds up heart rate and also boosts contractility. Thyroid hormone (T3) works on a slower timeline but sustains and amplifies this effect by increasing the expression of beta-adrenergic receptors and pacemaker channels, making the heart more responsive to catecholamines and capable of beating faster even at rest or with modest activity. Put together, these substances produce both immediate and lasting increases in heart rate.

The other options don’t produce the same clear, sustained increase. Acetylcholine acts on parasympathetic receptors to slow the heart. Cortisol can enhance sympathetic effects but is not a direct, rapid driver of heart rate in the same way catecholamines are. Insulin and glucagon don’t directly set the pace of the heart like that combination, and dopamine’s effect is more variable depending on dose.

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