Introduction to Thyroid Disorders

Question 1

What is the anatomical location and structure of the thyroid gland? [4]

Answer 1

located in the anterior neck over the trachea / between the C5-T1 vertebrae / divided into two lobes / which are connected by the isthmus (butterfly shaped gland)

Question 2

What are thyroid follicles composed of? [2]

Answer 2

sphere of follicular cells / surrounding a colloid containing core

Question 3

What is the process of iodide trapping? [5]

Answer 3

1. circulating iodide actively cotransported with Na+ ions / across basolateral membrane of follicular cells
2. Na+ ions pumped back out / whilst iodide ions diffuse across apical membrane of follicular cells / and are transported into the colloid

Question 4

How is thyroid hormone synthesised? [4, 2, 2]

Answer 4

1. inside the colloid / iodide oxidised to iodine / which binds to tyrosine residues on thyroglobulin molecules / via thyroid peroxidase
2. when thyroid is stimulated, T1 and T2 cleaved from tyrosine backbone / join to create T3 or T4
3. proteolysis of thyroglobulin / results in release of T3 and T4 into the blood

Question 5

What are the 2 thyroid hormones? [4, 3]

Answer 5

1. T4 (thyroxine) - mainly produced / less active than T3 / acts as reservoir for production of T3
2. T3 (triiodothyronine) - more active / 85% formed from peripheral conversion of T4 to T3 / via deiodinase enzymes

Question 6

How do thyroid hormones move around the body? [2]

Answer 6

most T4 and T3 is protein bound to thyroid binding globulin (TBG) / however the unbound portion is the active part

Question 7

What are the TFTs for hyperthyroidism? [3]

Answer 7

low TSH / high T4 / high T3

Question 8

What are the TFTs for hypothyroidism? [3]

Answer 8

high TSH / low T4 / low T3