Thyroid Hormone: What It Is & Function

What is Thyroid Hormone?

• Function: Controls the speed of metabolism.
• Importance: Critical for brain development in infants.
• Production: Made and released by the thyroid gland, a butterfly-shaped gland in the neck.
• Endocrine System: Part of the hormone system that coordinates bodily functions.
• Hormones Involved:
  • Thyroxine (T4): Largely inactive.
  • Triiodothyronine (T3): Active form, converted from T4 by certain organs.
  • Calcitonin: Helps regulate blood calcium levels, not involved in metabolism.

Control of Thyroid Hormone Levels

• Feedback Loop: Involves the hypothalamus, pituitary gland, and thyroid.
  • Hypothalamus: Releases TRH to stimulate the pituitary gland.
  • Pituitary Gland: Produces TSH to stimulate thyroid hormone production.
• Thyroid Hormones: 80% T4 and 20% T3; requires iodine.
• Regulation: Feedback prevents overproduction; issues can cause imbalances.

Function of Thyroid Hormone

• Conversion of T4 to T3: Occurs in liver, kidneys, muscles, thyroid, pituitary gland, brown adipose tissue, central nervous system.
• Effects:
  • Regulates metabolic rate (energy use).
  • Influences heart rate and body temperature.
  • Affects digestion speed.
  • Essential for brain development.
  • Controls muscle contractions.
  • Maintains skin and bone health.

Tests for Thyroid Levels

• Blood Tests:
  • Total T4 and Free T4 tests.
  • Total T3 and Free T3 tests.
  • TSH test.
• Additional Tests:
  • Thyroid antibodies for autoimmune conditions.
  • Thyroglobulin for thyroiditis and cancer monitoring.

Conditions Related to Abnormal Thyroid Levels

• Common Conditions:
  • Hypothyroidism (underactive thyroid).
  • Hashimoto's Disease (autoimmune hypothyroidism).
  • Hyperthyroidism (overactive thyroid).
  • Graves' Disease (autoimmune hyperthyroidism).
  • Thyroiditis, nodules, goiter, cancer.
• Causes: Issues with the hypothalamus or pituitary gland.

When to See a Doctor

• Symptoms of Imbalance:
  • Unexplained weight changes.
  • Heart rate irregularities.
  • Temperature intolerance, dry or moist skin.
  • Irregular menstrual cycles.
• Action: Consult a healthcare provider for blood tests if experiencing symptoms.