1a The Thyroid Gland Flashcards
How many lobe does a normal thyroid gland consist of?
2
What is the center of the two lobes of the thyroid gland called?
Isthmus
Which nerve runs close to the thyroid gland?
The left recurrent laryngeal nerve - supplies vocal cords
What are the two other glands embedded in the thyroid gland called?
The superior and inferior parathyroid glands
What are the parathyroid glands involved with?
The metabolism of calcium
Which nerve supplies the vocal cords?
The recurrent laryngeal nerve
What is the main function of the thyroid gland?
Metabolism regulation through the action thyroxine synthesis
Why must surgeons take care when performing surgery on the thyroid gland?
The parathyroid glands nearby are involved in calcium metabolism, so there is a risk they may be damaged
What is the function of the parathyroid glands?
Secrete parathyroid hormones
How do the parathyroid glands elevate calcium levels?
Elevate Ca2+ levels by degrading bone and stimulating calcium release, which increases the bodies ability to absorb calcium from food.
Where does the thyroid gland develop from?
The back of the throat
What is the name of the duct which divides into two lobes to form the thyroid gland?
Thyroglossal duct
What is lingual thyroid?
When the thyroid doesn’t develop down the thyroglossal duct, so doesnt get to the final position - results in a nodule at the back of the throat
By what week is the thyroid gland formed in the feotus?
Week 7
What is the pyramidal lobe?
Extension of the thyroid gland (remnant of thyroglossal duct); ~55% of individuals have it.
Describe how T3 and T4 are produced?
- TSH binds to TSH receptors on the follicular cell membrane
- This triggers a cascade of inttracellular reactions - secondary messenger systems
- Activates gene expression of TG - thyroglobulin
- Also, there is active transport of iodide ions into the follicular cell and then colloid through the sodium iodide symporter
- Iodide pumps on the basal membrane means iodide ions can enter into the colloid
- Iodination of the iodide ions into iodine
- Iodine then bind to tyrosine residue on TG in another iodination reaction forming MIT (3-monoiodotyrosine)
- Two iodines binding makes DIT (3,5diiodotyrosine)
- DIT + DIT = T4 = Thyroxine
- DIT + MIT = T3
What is the name of T3?
Tri-iodothyronine
Which of T3 and T4 is more active?
T3
What happens to T4
Gets deiodinated to form T3
What enzyme is used for deiodination?
Deiodinase
What is reverse T3?
an inactive form of T3 which forms when iodine is removed from the wrong place during deiodination
How do thyroid hormones travel in the blood?
they bind to plasma proteins
What are the three plasma proteins which thyroid hormones bind to?
Thyroid-binding globulin
Albumin
Prealbumin
What is the full name of t4
tetraiodothyronine
Where does most circulating T3 come from?
80% from deiodination of T4 by a deiodinase enzyme (T4→ T3)
20% from directly from thyroid secretion
What is the half life of T3?
2 days
What is the half life of T4?
7-9 days
What percentage of T3 and T4 are bioactive components (unbound)?
T3 - 0.5%
T4 - 0.05%