28/11/2025
🧠 Thyroid & Parathyroid Glands – Anatomy (Comprehensive Notes)
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🌟 1. THYROID GLAND — Overview
The largest endocrine gland in the body.
Produces: T3, T4 (metabolism) and calcitonin (calcium regulation).
Weight: ~20–25 g.
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📍 2. Location
• Lies in the anterior neck
• Deep to sternothyroid + sternohyoid muscles
• Extends from vertebral levels C5–T1
• Wraps around the trachea below the larynx
Parts:
• Right lobe
• Left lobe
• Isthmus → across 2nd–4th tracheal rings
• Pyramidal lobe (present in ~50%)
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🧩 3. Relations
Anterior:
• Strap muscles (sternohyoid, sternothyroid, omohyoid)
Posterolateral:
• Carotid sheath (CCA, IJV, vagus nerve)
Medial:
• Larynx
• Trachea
• Esophagus
• Recurrent laryngeal nerve (very important!)
Posterior:
• Parathyroid glands
• Prevertebral fascia
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🩸 4. Blood Supply
Arteries
• Superior thyroid artery (from external carotid)
• Inferior thyroid artery (from thyrocervical trunk → subclavian)
• Thyroid ima artery (variable, rare)
Veins
• Superior thyroid vein → IJV
• Middle thyroid vein → IJV
• Inferior thyroid vein → brachiocephalic vein
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🧠 5. Innervation
No secretomotor innervation—hormones regulate secretion.
• Sympathetic: cervical ganglia
• Parasympathetic: vagus
• Sensory: recurrent laryngeal nerve
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🔔 6. Lymphatic Drainage
• Prelaryngeal (Delphian) nodes
• Pretracheal nodes
• Paratracheal nodes
• Deep cervical nodes
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🧪 7. Parathyroid Glands — Overview
Small endocrine glands regulating calcium and phosphate via PTH.
Usually 4 glands:
• Superior pair (more constant position)
• Inferior pair (variable position)
Color: yellow-brown
Size: 6 × 3 × 1 mm
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📍 8. Location
On the posterior surface of the thyroid lobes:
Superior parathyroids:
• Constant
• Near the cricoid cartilage level
Inferior parathyroids:
• Variable
• May be found:
• Lower thyroid pole
• Thymus
• Anterior mediastinum
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🩸 9. Blood Supply
Same as thyroid:
Arteries:
• Mainly from inferior thyroid artery
Veins:
• Parathyroid veins → thyroid venous plexus
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🧠 10. Embryology (High-Yield)
Thyroid:
• From floor of primitive pharynx
• Migrates down → thyroglossal duct
• Foramen cecum = origin point
Parathyroids:
• Superior glands → 4th pharyngeal pouch
• Inferior glands → 3rd pouch (descend with thymus)
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🩺 11. Clinical Correlations
Goiter
• Enlarged thyroid
• Can compress trachea → dyspnea
• Dysphagia (esophageal compression)
Thyroidectomy
Risks:
• Injury to recurrent laryngeal nerve → hoarseness
• Injury to superior laryngeal nerve → voice pitch change
• Damage/removal of parathyroids → hypocalcemia
• Chvostek sign
• Trousseau sign
Ectopic thyroid tissue
• Lingual thyroid (most common)
• Along thyroglossal duct path
Parathyroid adenoma
• Causes hyperparathyroidism → kidney stones, bone pain (“stones, bones, groans”)
