Thyroid gland

1. Where is the thyroid gland?
In front of the neck (in front of the trachea and extends up to the thyroid cartilage)

2. Parts of the thyroid gland

True capsule- connective tissue capsule

False capsule- attached to the thyroid cartilage; gland moves up while swallowing

* Upper end of the pretracheal fascia is attached to the oblique thyroid cartilage, and connected to larynx so it moves up while swallowing

Relations

Anterior: strap muscles

Posterior: trachea and esophagus

Posterolateral: carotid arteries and internal jugular vein

Between tracheoesophageal groove: RLN

Retracting/ cutting sternohyoid and sternothyroid muscles will expose the thyroid gland

Parathyroid glands (2 pairs)

- mostly @ posterior surface of the thyroid gland/ sometimes embedded in gland

- Superior pair from 4th branchial arch

- Inferior pair from 3rd branchial arch

- Has chief cells (dark staining, arranged in clumps/ cords; secrete PTH) and oxyphil cells (scanty, pale staining)

3. Arterial supply of thyroid gland

• superior thyroid artery from external carotid artery
• inferior thyroid artery from internal carotid artery

Recurrent laryngeal nerve passes in between the branches of the inferior thyroid artery

• can be damaged during thyroid surgery
• if one side damaged: husky voice
• if both sides: no voice and stridor

4. Venous drainage of the thyroid gland

• Superior thyroid vein - internal jugular vein
• Middle thyroid vein- internal jugular vein
• inferior jugular vein - brachiocephalic vein

5. lymphatic drainage of the thyroid gland

Papillary carcinoma of the thyroid glands will spread to the lymph nodes

6. Microscopic structure of the thyroid gland

• Arranged as follicles lined by cuboidal epithelium
• follicular cells secrete thyroxine
• thyroxin binds to globulin = thryroglobulin aka colloid
• Parafollicular cells- secrete calcitonin to reduce plasma calcium levels
• medullary carcinoma

7. Development of the thyroid gland

Physiologically, the thyroglossal duct will close, but if not -> thyroglossal fistula

If parts of the tract persist -> thyroglossal cysts

If thyroid tissue remains along the tract -> ectopic thyroid