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Endocrine

Danielle Press

INTRODUCTION

Test Taking Tips

  • Aldosterone, electrolyte, and acid-base imbalances in adrenal disease are popular testing topics.

  • The MEN syndromes are also a favorite topic. Know these well, and understand when to operate and what operation to perform!

THYROID

EMBRYOLOGY, ANATOMY, AND PHYSIOLOGY

What embryologic structures does the thyroid originate from?

  • The medial thyroid comes from the first and second pharyngeal pouches

  • Lateral portions of the thyroid and parafollicular C cells arise from the fourth and fifth pharyngeal pouches

FIGURE 12-1

Anatomy of the thyroid gland and surrounding structures, viewed anteriorly. a., artery; n., nerve; v., vein. (Reproduced with permission from Brunicardi FC, Andersen DK, Billiar TR, et al. Schwartz’s Principles of Surgery, 11th ed. New York, NY: McGraw Hill; 2019.)

An illustration shows the anterior view of the anatomy of the thyroid gland and surrounding structures. The illustration shows the thyroid cartilage at the top followed by the pyramidal lobe that receives blood vessels and nerves such as the superior thyroid artery and vein from the common carotid artery along with the external carotid artery and internal jugular vein. The middle thyroid vein, inferior thyroid vein, and thyroidea ima a. (variable) are connected to the pyramidal lobe. The thyrocervical trunk is connected to the internal jugular vein.
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What is the arterial supply of the thyroid?

  • Superior thyroid artery (from external carotid artery)

  • Inferior thyroid artery (from thyrocervical trunk)

What is the venous drainage of the thyroid?

  • Superior and middle thyroid veins (drain into internal jugular vein)

  • Inferior thyroid veins (drain into innominate and brachiocephalic veins)

The recurrent laryngeal nerve innervates all of the muscles of the larynx except this muscle:

  • Cricothyroid muscle, which is innervated by the external branch of the superior laryngeal nerve

What structures do the recurrent laryngeal nerves wrap around?

  • Subclavian artery on the right

  • Arch of the aorta on the left

Injury to which nerve results in loss of projection and voice fatigability?

  • Superior laryngeal nerve

DRUGS

What is the mechanism of action of propylthiouracil (PTU) and methimazole?

  • Both drugs block peroxidase oxidation of iodide to iodine, thereby inhibiting incorporation of iodine into T4 and T3

  • PTU also inhibits peripheral conversion of T4 to T3

Which drug crosses the placenta: PTU or methimazole?

  • Methimazole

  • PTU is the safer choice in pregnancy

When steroids are given in severe or acute hyperthyroid conditions, how do they work?

  • Steroids inhibit peripheral conversion of T4 to T3 and lower serum TSH by suppressing the pituitary-thyroid axis

What is the Wolff-Chaikoff effect?

  • Large doses of iodine given after an antithyroid medication can inhibit thyroid hormone release by disrupting the coupling of iodide. This is a transient effect.

HYPERTHYROIDISM/HYPOTHYROIDISM AND GOITERS

What are the 3 most commons cause of hyperthyroidism?

  • Graves disease, ...

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