Thyroid Hormones Flashcards
(28 cards)
What are the two lateral lobes attached by?
Isthmus
What are thyroid epithelial cells?
Through the cells responsible for the synthesis of thyroid hormones and are arranged in Spears called thyroid follicles
What are the follicles filled with?
Filled with colloid which contains thyroglobulin which is the storage form of thyroid hormones
What’s T4?
Thyroxine (aka Tetraiodothyronine) – 90% of the hormones secreted
What’s T3
Triiodothyronine – 9% of the hormones secreted
Which thyroid hormone is the biologically active one?
T3 is. T4 is converted to T3
What is the purpose of iodine?
Iodine is important for normal quantities of thyroid hormone to be produced.
What’s the iron concentration like inside and outside of the cell?
30 x higher inside … iodide pump carries iodine from outside to inside
What’s thyroglobulin?
It’s a large glycoprotein composed of 140 tyrosine amino acids. Thyroid hormones are formed within the thyroglobulin.
Explain the pathway of thyroglobulin
Thyroglobulin is produced by follicular epithelial cells and pass through ER. It’s there stored in a membrane bound vesicles then it diffuses into lumen
Explain the oxidation of iodide
Iodide enters the follicular cell. It’s then oxidized by an enzyme called thyroid peroxidase, which is found on the lumen surface, oxidized iodide is formed.
What’s organification?
It’s the binding of iodine with the thyroglobulin active iodide added to tyrosine residues of thyroglobulin
What is tyrosine first iodized to?
Monoiodotyrodine (MIT) and diiodotyrosine (DIT)
What is coupling?
Coupling is when 2 iodotyrosine residues become coupled with each other
2 DITs couple to make ___
T4
1 DIT and 1 MIT couple to form ___
T3
Where are thyroid hormones stored?
As part of the TG in the lumen of the follicle (colloid)
How does thyroid hormone secretion occur?
First, apical surface sends out pseudopod extensions and a small portion of the colloid closes to form an endosome for endocytosis, then there’s a fusion of the endosome with the lysosome. Proteinases digest thyroglobulin and release T4 and T3.
What plasma proteins do thyroxine bind to?
Globulin and prealbumin mainly, but also albumin (to a low affinity)
How is T4 converted to T3
by the process of deiodination
What is TSH couple to
Adenylate cyclase
What regulates TSH secretion?
Electrical stimulation of hypothalamus increases, colt temp, emotional reactions
How do you thyroid hormones work?
Binding with thyroid hormones the receptors become activated and initiate transcription in the nucleus
What do thyroid hormones do
Increases synthesis of enzymes proteins etc. Essentially works to increase transcription in nucleus
Increases oxygen consumption and increases ion transport and glucose transport
