Why does increased thyroid hormone production, as seen in Graves' disease, lead to tachycardia (rapid heart rate)?

💡 Explanation

Elevated thyroid hormones upregulate the expression of beta-adrenergic receptors on cardiac myocytes. Because of this increased receptor density, the heart becomes more sensitive to catecholamines like epinephrine and norepinephrine, therefore increasing heart rate, rather than the reverse.

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