PBL 3: Thyroid Flashcards
The thyroid gland overlies which cartilaginous rings of the trachea
The second, third and fourth cartilaginous rings of the trachea
Each lateral lobe of the thyroid gland lies against the side of the ___ part of the trachea and the ____ end of the larynx
Each lateral lobe of the thyroid gland lies against the side of the upper part of the trachea and the lower end of the larynx
The isthmus is covered by what?
Isthmus is covered only by fascia and skin
The lobes of the thyroid are covered by?
The strap muscles and overlapped by sternocleidomastoid muscle
What is the blood supply to the thyroid gland
Blood supply via superior and inferior thyroid arteries
The superior thyroid artery is the first branch of the external carotid artery and it supplies the superior and anterior portions of the gland.
The inferior thyroid artery arises from the thyrocervical trunk (which in turn is a branch of the subclavian artery) and it supply the posteroinferior aspect of the gland.
Describe the venous drainage of the thyroid gland
Venous drainage is carried out by the superior, middle and inferior thyroid veins, which form a venous plexus.
The superior and middle veins drain into the internal jugular veins, whereas the inferior drains into the brachiocephalic vein.
The superior and middle thyroid veins drain into the ____ veins, whereas the inferior thyroid veins drains into the ____ vein.
The superior and middle veins drain into the internal jugular veins, whereas the inferior drains into the brachiocephalic vein.
Describe the histology of the thyroid gland
- Made up of units of follicles.
- Each follicle consist of a wall made from primarily of follicular cells, most of which extend into the lumen of the follicle. In the center of a follicle is a a lumen filled with colloid
- Between the follicles there are the fenestrated epithelium in which the hormoned produced by the follicular cells enter the circulation. Moreover, there is clear cells which produce the hormone calcitonin
Describe the composition of the follicular cells
Inactive follicular cell is shaped as a low cuboidal to squamous
Under influence of TSH, the follicular cells are active and change shape and become more cuboidal to low columnar
Iodide is transported from the vasculature across the basolateral membrane into the follicular cell by which transporter
Na+I- synporter
Iodide (I-) is transported across the apical membrane of the follicular cell by which transporter?
Chloride/Iodide synporter
Describe the oxidation process that occurs in the colloid of the thyroid gland
Iodide is converted to Iodine by thyroid peroxidase
Define Bradycardia
Slow heart rate
Cold intolerance is associated with hypo or hyperthyroidism
Hypothyroidism
What are the major environmental triggers of autoimmune thyroid disease
- Iodine
- Medications
- Infection
- Smoke
- Possible stress
Describe the mechanism of action of carbimazole
It works by inhibiting the thyroid peroxidases (TPO) that catalyze the iodination of iodide into iodine
Describe the mechanism of action of propylthiouracil
PTU inhibits iodine and peroxidase from their normal interactions with thyroglobulin to form T4 and T3.
Name the proteins that transports thyroid hormones in the plasma
Thyroxine-binding globulin (main one)
Also albumin (but it is not the main transport protein)
Name two components derived from the diet that are required for the synthesis of thyroid hormones
Iodide
Tyrosine
What results would you expect from the thyroid function tests to confirm a diagnosis of primary hyperthyroidism
Low TSH
High T3 and T4
