Thyroid Gland Flashcards
Where is the thyroid gland located?
under the larynx or “adams apple”, on top of the trachea
What are the different parts of the thyroid gland?
2 LOBES of the thyroid gland, connected by thyroid connective tissue called ISTHMUS, which is topped with a PYRAMID, which is all under the thyroid cartilage.
How are the follicles of the thyroid gland lobes arranged?
Follicles are units of colloid (a cavity filled w/ sticky fluid) surrounded by follicular cells in a circular arrangement, and further surrounded by parafollicular cells.
What nerve runs close to the thyroid gland?
left recurrent laryngeal nerve (which supplies the vocal cords)
What is the embryology of the thyroid gland?
develops from the floor of the pharynx (base of the tongue), then occurs the development of the thyroglossal duct, divides into 2 lobes + duct disappears leaving the FORAMEN CAECUM, reaching final position in the neck by 7th week.
How is the thyroid gland stimulated to produce Thyroid Hormone?
stimulated by TSH, released by the anterior pituitary gland
How does TSH first enter the thyroid gland?
TSH in the bloodstream binds to the TSH-R (TSH-receptor) embedded into the follicular cell membranes of the thyroid gland.
What ion is necessary for TH production? How is this ion used?
Iodide ions : when TSH binds, Iodide ions are actively transported across the follicular cell membrane to colloid where it’s IODINATED (oxidised).
What is Thyroglobulin? Why is it important in TH production?
a glycoprotein produced in follicular cells and released into the colloid when TSH binds - it’s combined with the iodide ions in iodination reactions in order to produce TH.
What is TPO? Why is it important in TH production?
Thyroid Peroxidase gets activated when TSH binds, catalyses the iodination reactions along with H202 (hydrogen peroxide).
What forms when TG combines with Iodide ions?
one of two products: MIT (mono-iodo-tyrosine) or DIT (di-iodo-tyrosine)
What is the importance of MIT and DIT in TH production?
a coupling reaction between MIT + DIT produces T3, a coupling reaction between 2 DITs produces T4
What is T3?
triiodothyronine, the active form of TH
What is T4?
thyroxine, the prohormone of TH
What’s the difference between T3 and T4?
T4 is the precursor + gets converted into T3
Does the thyroid gland produce more T3 or T4?
T4
How is T4 converted into T3?
deiodination reaction using the enzyme DEIODINASE
What is “reverse T3” and how is it produced?
inactive form of T3, created through deiodination of T4 in a different position
What percentage of circulating T3 is due to direct thyroidal secretion?
20%
What percentage of circulating T3 is due to deiodination of T4?
80%
How are T3 and T4 transported in the blood?
mostly by binding to plasma proteins
What plasma protein are T3 + T4 bound to 70-80% of the time?
TBG (thyroid-binding globulin)
What plasma protein are T3 + T4 bound to 10-15% of the time?
albumin