QS Study

The thyroid is an endocrine gland, situated in the lower part the front and sides of the neck. Grossly, the gland appears brownish-red and the left and right lobes are connected by an isthmus.

Blood supply

Blood supply to the thyroid gland is achieved by two main arteries; the superior and inferior thyroid arteries. These are paired arteries arising on both the left and right.

(A) Arterial supply:

(i) Superior thyroid artery: Supplies the upper 1/3rd of the lobe & upper 1/2 isthmus. It is related to the external laryngeal nerve, pierces the thyroid fascia and then divides into anterior and posterior branches.

(ii) Inferior thyroid artery: Supplies lower 2/3rd of the lobe & lower 1/2 of the isthmus. It arises from the thyrocervical trunk of the subclavian artery, crosses beneath the carotid sheath and enters the lower or middle part of each thyroid lobe and divides into superior and inferior thyroid branches to supply the inferior and posterior surfaces of the gland.

(B) Venous drainage:

  1. Superior thyroid vein- drains into a common facial vein.
  2. Middle thyroid vein- drains into the internal jugular vein.
  3. Inferior thyroid vein- drains into brachiocephalic vein.

Equally important is the venous drainage, which is achieved by the inferior, middle and superior thyroid veins. The superior thyroid vein travels with the superior thyroid artery from the superior part of the gland. Superior and middle thyroid veins drain into internal jugular vein whereas the inferior drains mostly into the left brachiocephalic vein. The superior and middle thyroid veins drain into the internal jugular vein. The inferior thyroid veins anastomose with each other and drain into the left brachiocephalic vein in the thorax.

Blood Supply of Thyroid Gland 1

Fig: Blood Supply of Thyroid Gland

Lymphatic vessels

The lymphatic vessels of the thyroid gland run in the interlobular connective tissue, usually accompanying the arteries and form a capsular network of lymphatic vessels. It is multi-directional and initial lymph drainage is to peri-thyroid lymph nodes then onto prelaryngeal, pretracheal and paratracheal nodes (level 6 lymph nodes).

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