Thyroid hormone regulation and synthesis

Question 1

1. Describe the uptake of iodine from plasma by the thyroid gland.

Answer 1

Linked to Iodide sodium symport, sodium recycled out by the sodium potassium ATPAse

Question 2

2. Explain the synthesis and release of thyroglobulin into the lumen of the thyroid follicle.

Answer 2

made by follicular cells, by chainsof tyrosine residues, secreted into the lumen as a lumenal colloid

Question 3

3. Identify the steps in thyroid hormone synthesis and its release into the blood.

Answer 3

Thyroperoxidase (TPO) makes I into reactive I and throws an I on a tyrosine. Tyrosines become mono or diiodinated. TPo also ether links tyrosines, the the thyroglobulin molecule is then moved back to the follicular cells where it is degraded in the lysosome, where T4 is released. T4–> T3 by monoiodinase

Question 4

4. Describe the transport of thyroid hormones in the plasma.

Answer 4

where T4 is released. T4–> T3 by monoiodinase
99% bound to thyroglobulin binding protein
1% free

Question 5

5. Categorize the actions of thyroid hormone.

Answer 5

• regulates metabolic function
• important in development by being permissive on other hormones

increases number and efficacy of Beta adrenergic receptors

helps brain development and regulates depression

Question 6

6. Diagram the normal regulation of thyroid hormone levels by the hypothalamic-pituitary axis.

Answer 6

T3 neg regs

TSH

• regulates follicular cell #
• iodide uptake
• TPO and thyroglobulin
• promotes organification of Iodide