Endocrinology 12 Flashcards
What are the basic functional units of the thyroid?
Thyroid follicles
What do the follicles contain in their center?
Colloid
What does colloid contain?
The storage form of the steroid hormone
What is the colloid surrounded by?
A single layer of epithelial cells/follicular cells
What is the colloid and follicular cells like in a resting state?
In a resting state the follicular cells are small and the colloid is large because its storing the hormone
What is the colloid and follicular cells like in a acting state?
The colloid in the center is smaller because hormones are being secreted and the follicular cells are large
Where are parafollicular cells found?
In between the thyroid follicles
What are parafollicular cells/c-cells the source of?
Calcitonin
What amino acid are thyroid hormones derived from?
Tyrosine
What does Tyrosine bind to in the thyroid?
Iodine
What is Monoiodotyrosine (MIT) or diiodotyrosine?
An intermediate molecule that forms when tyrosine binds to one or two iodine
What are the active Thyroid hormones?
- Triiodothyronine (T3)
* Tetraiodothyronine (thyroxine, T4)
How Does Iodide get from the blood to the thyroid?
By active transport
What is Thyroglobulin?
A large glycoprotein that contains tyrosine units
What are MIT and DIT formed on?
The backbone of the thyroglobulin molecule
What can give T3?
Coupling of MIT and DIT
What can give T4?
Coupling of DIT and DIT
Where are T3 and T4 stored?
In the colloid
Which thyroid hormone is there a greater amount of in the colloid?
T4
What is the basolateral side of the follicular cell facing?
Blood vessels
What is the apical membrane of the follicular cell facing?
The colloid
What pump brings iodine from the blood into the follicular cells?
The sodium iodide pump couples the movement of sodium out of the blood with the movement of iodine
What happens once iodide is in the follicular cell?
It leaves the cell through the apical membrane and moves into the colloid
What is thyroglobulin secreted from and where does it go?
It is secreted from follicular cells into the colloid
What is Thyroglobulin?
A long chain of amino acids (a protein) with tyrosine residues
What does the oxidized iodide in the colloid do?
Combines with tyrosine residues in the thyroglobulin molecule
What is the catalyst for thyroglobulin tyrosine and iodine combining?
Peroxidase
what makes up the bulk of the colloid?
Thyroglobulin with MITs and DITs
What movement is required for hormones to be secreted from the thyroid?
They have to move from the colloid through the cell and into the blood through endo and exocytosis
What removes the MIT and DIT from thyroglobulin to be T3 and T4?
Lysosomes
In what form are T3 and T4 mainly found in the blood?
A bound form to a plasma protein (they are rarely in a free form)
What are the characteristics of a hormone in the bound form?
They are not active
What does T4 act largely as?
A precursor for T3
Where are thyroid hormone receptors found?
In the cell nucleus bound to genetic material
Which thyroid hormone binds more strongly to the receptor?
T3
What is the half life of thyroid hormones?
1-7 days
