Thyroid Function and Hyperthyroidism

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Thyroid Function and Hyperthyroidism

Overview of the Thyroid Gland

• Location:
  • Largest endocrine gland, positioned anterior and lateral to the trachea and inferior to the larynx.
• Function:
  • Secretes thyroid hormone, which:
    • Increases metabolic rate by raising respiratory rate and heart rate.
    • Accelerates the breakdown of food for fuel.
    • Enhances heat production.
• Regulation:
  • Works in a negative feedback loop with the hypothalamus and pituitary gland to regulate metabolic rate:
    1. Low thyroid hormone → Hypothalamus releases thyrotropin-releasing hormone (TRH).
    2. TRH stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH).
    3. TSH signals the thyroid to secrete triiodothyronine (T3) and thyroxine (T4) into the bloodstream.
    4. Elevated thyroxine levels inhibit hypothalamic TRH production, maintaining metabolic balance.

Hyperthyroidism

• Definition:
  • A condition of chronically high thyroid hormone levels in the blood.
• Common Cause:
  • Graves' disease: An autoimmune disorder where B-cells produce thyroid-stimulating immunoglobulins (TSIs).
    • TSIs mimic TSH, binding to TSH receptors on thyroid cells.
    • This overstimulates the thyroid gland, leading to excessive hormone production.
• Effects of Hyperthyroidism:
  • Increased metabolic activity:
    • Respiration rate and heart rate (tachycardia).
    • Enhanced heat production.
  • Thyroid enlargement (thyroid hypertrophy or goiter).

Treatment Options

1. Antithyroid Drugs:
   • Examples: Propylthiouracil and Methimazole.
   • Mechanism: Suppress thyroid hormone synthesis.
2. Surgery:
   • Partial or total removal of thyroid tissue to reduce hormone secretion.
3. Radioactive Iodine Therapy:
   • Oral ingestion of radioactive iodine destroys thyroid tissue, reducing hormone secretion.