Regulation of Thyroid Hormone Synthesis

Question 1

Thyroid hormone is a _________-derived hormone.

Answer 1

tyrosine

Question 2

The skeleton of thyroid hormone is ___________.

Answer 2

thyronine

Question 3

The thyroid hormone is made hydrophobic by ___________.

Answer 3

its ether linkage

Question 4

The full name of T4 is ________________.

Answer 4

3,5,3’,5’–tetraiodothyronine (also called thyroxine)

Question 5

The full name of T3 is _________________.

Answer 5

3,5,3’–triiodothyronine

Question 6

The thyroid has a copious blood supply. One of the reasons this is thought to be so is _____________.

Answer 6

that iodide is a trace element in water, and in the natural world we would need to absorb as much iodide from the water as possible

Question 7

How is iodide absorbed by thyroid follicular cells?

Answer 7

By a sodium/iodide symporter (the intracellular sodium is then pumped back out through a Na/K antiporter)

Question 8

The thyroid follicular cells secretes ____________ into the lumen of the thyroid.

Answer 8

thyroglobulin

Question 9

Thyroglobulin is used entirely within _____________.

Answer 9

the thyroid gland

Question 10

Each thyroglobulin protein contains approximately ____________ tyrosine residues that can be used to make T4.

Answer 10

20 (although there are many more tyrosine residues)

Question 11

Thyroglobulin is made in a non-iodinated form that then gets _________________.

Answer 11

secreted by the thyroid follicular epithelium into the follicular colloid

Question 12

Thyroglobulin gets iodinated in the ______________.

Answer 12

colloid and then taken up by endocytosis back into the thyroid follicular epithelium

Question 13

T3 and T4 bind _______________.

Answer 13

nuclear receptors

Question 14

Low levels of T3 induce a metabolic shift to ____________.

Answer 14

anabolism

Question 15

High levels of T3 induce a metabolic shift to ______________.

Answer 15

catabolism

Question 16

High levels of thyroid hormone stimulate which adrenergic receptor?

Answer 16

Beta-1

Question 17

TSH regulates which points of thyroid production and release?

Answer 17

• Growth of follicular cells
• Transporters
• Thyroperoxidase
• Thyroglobulin
• Organification of iodide (putting free iodide onto protein)
• Endocytosis of thyroglobulin from the colloid

Question 18

The primary constituent of the colloid is _______________.

Answer 18

thyroglobulin

Question 19

Where is thyroperoxidase?

Answer 19

In the colloid, bound to the membrane

Question 20

What are DIT and MIT?

Answer 20

Diiodotyrosine and monoiodotyrosine –these couple to form triiodothyronine

Question 21

Where are T4 and T3 cleaved from thyroglobulin?

Answer 21

In follicular lysosomes

Question 22

_____________ has a longer half-life.

Answer 22

T4 (another reason thyroxine is given pharmaceutically)

Question 23

Why does thyrotoxicity mimic catecholamine overdose?

Answer 23

Because thyroid hormone potentiates the effects of catecholamines

Question 24

List five effects of thyroid hormone.

Answer 24

• Increased basal metabolic rate
• Potentiation of catecholamine effects
• Promotes linear growth throughout childhood
• Promotes brain development throughout childhood
• Promotes anabolic effect at low doses and catabolic effect at high doses