04/01/2026
Thyroid Gland :-
🔹 Anatomy
→ Butterfly-shaped endocrine gland
→ Location: Anterior neck, below larynx, in front of trachea
→ Weight: ~15–25 g (adult)
→ Parts:
Right lobe
Left lobe
Isthmus
→ Highly vascular gland
→ Structural unit: Thyroid follicle (lined by cuboidal epithelium)
🔹 Physiology
🟡 Hormones Secreted
Thyroxine (T4)
Triiodothyronine (T3)
Calcitonin (from parafollicular / C cells)
→ T3 is 3–5 times more active than T4
→ Iodine is essential for hormone synthesis
→ Hormones stored as thyroglobulin in follicles
🔹 Regulation
→ Controlled by Hypothalamic–Pituitary–Thyroid axis
TRH (Hypothalamus)
⬇
TSH (Anterior Pituitary)
⬇
T3 & T4 secretion (Thyroid)
→ Negative feedback by T3 & T4
🔹 Functions
🟢 Metabolic Functions
→ Regulates Basal Metabolic Rate (BMR)
→ Increases oxygen consumption
→ Increases heat production
🟢 Growth & Development
→ Essential for normal growth
→ Critical for brain development in infants & children
🟢 Cardiovascular System
→ Increases heart rate
→ Increases cardiac output
🟢 Nervous System
→ Maintains alertness
→ Supports normal mental activity
🟢 Bone & Calcium Metabolism
→ Calcitonin lowers blood calcium level
→ Prevents excessive bone resorption
🔹 Disorders
Hypothyroidism
→ ↓ T3 & T4
→ Weight gain, cold intolerance, fatigue, constipation
Hyperthyroidism
→ ↑ T3 & T4
→ Weight loss, heat intolerance, palpitations, tremors
Goiter
→ Enlargement of thyroid due to iodine deficiency
🔑 Key Points
→ Thyroid hormones affect almost every cell of the body
→ Iodine deficiency is the most common cause of goiter
→ Essential for metabolism, growth & development
📌 Disclaimer
For Educational and Information ℹ️ Purpose Only
