The thyroid gland plays a central role in regulating metabolism, growth, and development by producing T3 and T4. Hyperthyroidism increases the metabolic rate, leading to systemic effects. In Graves' disease, autoantibodies continuously stimulate TSH receptors in the thyroid, causing excessive production of thyroid hormones, despite the body's feedback mechanisms. This results in high levels of free T3 and T4 in the bloodstream, which suppresses TSH production through negative feedback.
Excess thyroid hormones impact nearly every organ system. Cardiovascular effects include increased heart rate, palpitations, hypertension, and the risk of heart failure due to increased cardiac output. Hyperthyroidism also causes heat intolerance, excessive sweating, and weight loss despite increased appetite. The nervous system is affected as well, leading to tremors, anxiety, insomnia, and hyperactivity. In severe cases, hyperthyroidism can result in a thyroid storm, a life-threatening crisis marked by fever, tachycardia, and multi-organ failure.
Pregnancy naturally alters thyroid function due to the increase in thyroxine-binding globulin (TBG) from elevated estrogen, which raises total T4 and T3 levels. Additionally, hCG, produced by the placenta, can stimulate TSH receptors in the first trimester, causing a transient rise in free T4. Normally, these changes are regulated by the body, but in women with hyperthyroidism, the excess thyroid hormone exacerbates these physiological adjustments.
