Lecture on Thyroid Gland

Introduction

• The thyroid is a butterfly-shaped endocrine gland located in the neck, wrapping around the trachea below the thyroid cartilage (Adam’s apple).

Major Hormones

• Triiodothyronine (T3) and Thyroxine (T4)
  • Numbers 3 and 4 represent the number of iodine atoms in each hormone.
  • Collectively referred to as thyroid hormones.

Regulation of Thyroid Hormones

• Secretion controlled by Thyroid-Stimulating Hormone (TSH) from the anterior pituitary.
  • TSH is induced by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus.
• Regulated by a negative feedback loop:
  • High levels of thyroid hormones suppress the production of TSH and TRH, inhibiting further production of thyroid hormones.

Functions of Thyroid Hormones

• Increase metabolic rate:
  • Stimulate appetite, digestion, nutrient breakdown, and absorption.
  • Increase oxygen consumption, breathing rate, heart rate, and contraction strength.
  • Result in increased heat production.
• Important for bone growth and fetal brain development.

Thyroid Disorders

Hypothyroidism

• Definition: Insufficient production of thyroid hormones.
• Symptoms: Fatigue, weight gain despite poor appetite, cold intolerance, slow heart rate, heavy menstrual bleeding, constipation.
• Common Causes: Iodine deficiency, Hashimoto's thyroiditis (an autoimmune disease).
  • Can lead to goiter due to increased TSH production stimulating thyroid growth.
• Management: Thyroxine hormone replacement.

Hyperthyroidism

• Definition: Excessive production of thyroid hormones.
• Symptoms: Irritability, insomnia, weight loss despite good appetite, heat intolerance, heart racing, diarrhea.
• Common Causes: Graves' disease (an autoimmune disorder).
  • Characterized by thyroid-stimulating immunoglobulin (TSI) leading to uncontrolled hormone production and possible goiter.
• Management: Drugs to suppress thyroid function, radioactive iodine, or surgery to remove part of the thyroid gland.