7) Thyroid Gland Flashcards
What are the three structures that produce hormones as part of the thyroid gland?
- Thyroid gland
- Parathyroid gland
- C-cells
Where is the thyroid gland located?
Below the larynx
What are the functional units of the thyroid gland?
Thyroid follicles
What is the structure of thyroid follicles?
Single layer of epithelial cells surrounding a lumen that contains colloid
Are thyroid hormones stored or secreted immediately following synthesis? Why is this particular?
Thyroid hormones are lipophilic, but they are capable of being stored within the colloid of the thyroid follicles (7-8 weeks)
What controls blood flow to the pituitary gland?
Postganglionic sympathetic nerves
What regulates T4 and T3 release?
Blood flow by affecting the delivery of TSH, iodine, and nutrients
How do thyroid follicles differ in the underactive and overactive state?
- Underactive: expansion of the colloid
- Overactive: expansion of the follicles, decrease in colloid
Where are C-cells contained?
Within the walls of the follicle
What are the two biologically active forms of thyroid hormone?
- T4
- T3
What are the two inactive forms of thyroid hormone? How are they produced?
- reverse-T3 (deiodination of T4)
- T2 (deiodination of T3)
What are the six steps required for the synthesis of T3 and T4? (6)
1) Active transport of iodine into the thyroid cell
2) Oxidation of iodide and iodination of thyroglobulin
3) Linking pairs of iodotyrosines in thyroglobulin to form T3 and T4
4) Proteolysis of thyroglobulin to release T3 and T4
5) Deiodination of iodotyrosines in thyroid cell and recycling of iodine
6) Intrathyroidal 5-deiodination of T4 to T3
What is the active transport of iodine into the thyroid cell referred as?
Trapping
What is oxidation of iodide and iodination of thyroglobulin referred as?
Organification
What is iodinated in thyroglobulin?
Tyrosyl residues
What is linking pairs of iodotyrosines in thyroglobulin to form T3 and T4 referred as?
Coupling
How is T4 converted to T3 within the thyroid?
5’-deiodination
What three components must be present for thyroid hormone synthesis?
1) Na+/I- symporter
2) Thyroglobulin
3) Thyroid peroxidase
What are the two major effects of TSH binding to its cognate receptor?
- Growth of the cell
- Synthesis of thyroid hormones
Which GPCRs do TSH-receptors contain?
- Gs
- Gq
How is iodide transported into the thyroid follicle cell from the extracellular fluid?
- Na+/I- symporter
- Na+ is brought back to the extracellular fluid with an ATPase
What are the two functions of thyroid peroxidase?
1) Iodination reaction
2) Couple MIT and DIT on the thyroglobulin molecule itself
What is the function of lysozyme in the synthesis of thyroid hormones?
Proteolytic breakdown of thyroglobulin, releasing compounds for recycling, and T3/T4
Which negative anions in the extracellular fluid block the active transport of iodine?
- ClO4-
- SCN-
- Bromide
- Nitrite