Thyroid Gland and Thyroid Hormones

Jun 28, 2024

Thyroid Gland and Thyroid Hormones

Introduction

  • Discussing the thyroid gland and its hormones (T3 and T4).
  • T4: More abundant.
  • T3: More active.
  • Thyroid hormone increases metabolic rate.

Hormonal Hierarchy

  • Hypothalamus (CEO): Secretes TRH (Thyrotropin Releasing Hormone).
  • Pituitary (General Manager): Secretes TSH (Thyroid Stimulating Hormone) upon TRH stimulation.
  • Thyroid Gland (Employee): Secretes T3 and T4 in response to TSH.
  • Independent Contractors: Parathyroid, adrenal medulla, and pancreas.

Negative Feedback Mechanism

  • High thyroid hormone levels inhibit TRH from the hypothalamus and TSH from the anterior pituitary.

Hypothyroidism

  • Symptoms: Low metabolic rate, tiredness, laziness, depression, obesity, constipation.
  • Categories:
    • Primary Hypothyroidism: Problem in the thyroid gland.
    • Secondary Hypothyroidism: Problem in the anterior pituitary.
    • Tertiary Hypothyroidism: Problem in the hypothalamus.

Raw Materials for Thyroid Hormone

  • Tyrosine: Derived from phenylalanine (obtained from foods).
  • Iodine: Obtained from diet (e.g., iodized salt, sea food).

Thyroid Gland Anatomy

  • Located in the neck.
  • Near the arch of the aorta.
  • Secretes T4, T3, reverse T3, calcitonin.
  • Thyroid Follicles: Produce thyroid hormone.
  • Para-follicular (C) Cells: Produce calcitonin.

Thyroid Hormone Production

  1. Iodide Trapping: Iodide from the bloodstream enters the thyroid gland.
  2. Oxidation: Iodide converted to iodine.
  3. Organification: Iodine binds with thyroglobulin (contains tyrosine) to form MIT and DIT.
  4. Coupling: MIT + DIT = T3, DIT + DIT = T4.
  5. Release: T3 and T4 released into the bloodstream.
  • Enzyme: Thyroperoxidase is essential for oxidation, organification, and coupling.

Effects of TSH

  • Stimulates thyroid hormone synthesis and enlarges thyroid gland (goiter).

Metabolism

  • Thyroid Hormone: Increases basal metabolic rate, protein catabolic, glycogen catabolic, triglycerides catabolic.
  • Role in Brain Development: Essential during embryology and childhood.
  • Catecholamines: Increases beta-receptor sensitivity.
  • Reproductive Health: Boosts ovarian cycle in females, spermatogenesis in males.
  • Gastrointestinal Motility: Too much = diarrhea, too little = constipation.

Hyperthyroidism vs Hypothyroidism Symptoms

  • Hypothyroidism: Bradycardia, cold intolerance, constipation, coarse hair, depression, dry skin, lethargy, weight gain.
  • Hyperthyroidism: Tachycardia, nervousness, heat intolerance, diarrhea, silky hair, weight loss, goiter, exophthalmus.
  • Diagnosing hyperthyroidism: Old vs. current photos.

Practical Recommendations

  • Focus on symptoms first when learning about thyroid disorders.

Conclusion

  • Check out additional resources and courses for deeper understanding.
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