Anatomy of the Thyroid Gland

Overview

• Thyroid Gland: Butterfly-shaped endocrine organ near the trachea.
• Hormones:
  • Triiodothyronine (T3) and Thyroxine (T4): Important for metabolism.
  • Calcitonin: Regulates calcium homeostasis.

Structure

• Lobes: Two main lobes - right and left, joined anteriorly by the isthmus.
• Parathyroid Glands: Four in total, located posteriorly, two on each side.
• Pyramidal Lobe: Often seen in 55% of people, arises from the thyroglossal duct.

Development

• Gestational Activity: Active by the 24th week of gestation, important for fetal development.
• Embryological Descent: Begins at the foramen cecum at the base of the tongue and moves down to the trachea.
• Thyroglossal Duct Cyst: Arises when the thyroglossal duct does not atrophy.

Location

• Visceral Compartment of the Neck: Alongside trachea, recurrent laryngeal nerve, esophagus, and pharynx.
• Anchored by Pre-tracheal Fascia: Thyroid moves with swallowing.
• Vertebral Level: C5 to T1.

Blood Supply

• Arteries:
  • Superior Thyroid Artery (from external carotid artery).
  • Inferior Thyroid Artery (from thyrocervical trunk of subclavian artery).
  • Ema Artery (in 3% of people, from brachiocephalic artery).
• Venous Drainage:
  • Supra- and Middle Thyroid Veins to Internal Jugular Vein -> Brachiocephalic Vein -> Superior Vena Cava.

Nerve Supply

• Sympathetic Nerves: From cervical ganglion.
• Parasympathetic Nerves:
  • Vagus Nerve branches to form superior and recurrent laryngeal nerves (supplies laryngeal muscles).
  • Importance in speech and potential risk during thyroidectomy.

Histology

• Follicles: Functional units, central cavity filled with colloid surrounded by epithelial cells.
• Colloid: Site of thyroid hormone production.
• Parafollicular Cells (C cells): Produce calcitonin.

Lymphatic Drainage

• Lymph Nodes:
  • Pre-tracheal, para-tracheal, inferior/superior deep cervical, pre-laryngeal, submandibular, and submental.
• Clinical Relevance: Potential spread of thyroid cancer.

Clinical Anatomy

• Tubercle of Zuckerkandl: Extension of thyroid, aids in identifying recurrent laryngeal nerves during surgery.

Conclusion

• Importance of understanding thyroid anatomy for clinical procedures and pathology.