What is the innervation of the thyroid gland ?
- Parasympathetic from vagus nerve
- Sympathetic from superior middle and inferior ganglia of sympathetic trunk
Describe the blood supply of the thyroid gland
Superior and inferior thryoid arteries +/- thyroida ima
Describe the venous drainage of the thyroid gland
3 pairs of veins - superior/middle thyroid vein ==> internal jugular
inferior thyroid vein ==> brachiocephalic vein
What is the thyroid gland supported by ?
Ligaments and strap muscles
What is the main ligament which supports the thyroid gland ?
The posterior suspensory ligament (berry ligament)
What is there a risk of injuring during surgery on the thyroid ?
- Injury to the vasculature
- Injury to the recurrent laryngeal nerve
What are the 3 primary features of thyroid glands under the microscope ?
- Follicular cells
- Parafollicular cells
What are follicles in the thyroid ?
Small spherical groupings of cells that consist of a rim of follicular cells which surround the colloid
What are parafollicular cells ?
Scattered amoung follicular cells and the spaces between follicles
What is the colloid ?
Tyrosine containing thyroglobulin filled spheres enclosed by follicular cells
What do follicles play a key role in ?
What is the function of follicular cells ?
- When stimulated by TSH
- Secrete thyroid hormones T3 and T4
What is the function of parafollicular cells ?
What is the overall idea of synthesis and secretion in the thyroid gland ?
Iodine (the fuel) comes in and then T3/T4 (products) come out
Describe the stages of synthesis of T3 & T4
- Iodine taken up by follicular cells
- Iodine attaches to tyrosine residues on thyroglobulin to form MIT and DIT
- MIT = monoiodotyrosine unit, DIT - Diiodotyrosine unit
- Coupling of MIT and DIT = T3 (triiodotyrosine unit)
- Coupling of 2 DIT's = T4 (thyroxine)
- T3 and T4 are then stored in colloid till required
What is the major biologically acitve thyroid hormone ?
T3 - it is roughly 4 times more potnet but 90% of thyroid hormones secreted is T4
Where is T4 converted to T3 ?
Converted in the liver and kidney
What is the function of Deiodinase enzymes ?
To either activate or deactivate thyroid hormones
There is 3 types:
Which Deiodinase enzyme converts T4 into T3 ?
D2 in the tissues