L15-16 Thyroid Gland Flashcards
What is the largest endocrine gland
Thyroid
When you’re a little baby growing in your mommy’s tumtum, when does your thyroid gland start secreting thyroid hormone and why?
12 weeks gestation
Thyroid hormone helps myelinate the CNS and is critical in the growth of the fetus
What will happen if the fetus doesn’t have thyroid hormone?
Cretinism
What is the functional unit of the thyroid?
Follicular cell
What kind of cells release calcitonin?
Parafollicular cells
Where in the thyroid are hormones stored?
Colloid
In hyperthyroidism, what happens to the colloid?
Colloid gets reabsorbed
=increased production and release of TH into plasma
What happens to the colloid in hypothyroidism?
Decreased colloid reabsorption and thyroid hormone synthesis
What are the 4 main steps in the synthesis of thyroid hormones, and what hormone must be present for them to happen?
- Uptake of iodide from plasma
- Incorporation/Organification- putting iodide and tyrosine together
- Coupling of iodinated tyrosine to form the thyroid hormone
- Diffusion of T3 and T4 into blood
TSH is critical for every one of these steps!!!*****
NO TSH= THESE THINGS ARE NOT GONNA HAPPEN
Where are thyrotrophs?
In the pituitary gland
Which organ releases TRH?
Hypothalamus
What kind of cells does TRH target
Thyrotrophs in the pituitary
What cells are the target of TSH
Follicular cells in thyroid
TSH receptor activation results in _____________
Stimulation of all steps in thyroid hormone synthesis
Uptake, organification, coupling, and release of thyroid hormones
Biological effects of TSH
Stimulation and gene transcription of:
1. Na-Iodide symporter
- Thyroglobulin (Tg)
- Thyroid peroxidase (TPO)
- Synthesis of T3 and T4
What does the Na-Iodide symporter do?
Sucks up iodide from blood
What does thyroglobulin (Tg) do?
Its a glycoprotein that serves as a scaffold for tyrosine iodination as well as storage of thyroid hormone
(Tg contains all the tyrosine the thyroid needs)
What does thyroid peroxidase (TPO) do?
Enzyme involved in the oxidation of iodide and its incorporation into tyrosine residues of Tg
Where does synthesis of T3 and T4 occur?
In the cytosol of follicular cell AND the colloid
**synthesis is both intracellular and extracellular*
Which is a prohormone: T3 or T4
T4. It is not the most active form of thyroid hormone
Where does iodide come from?
Diet
What is the average daily intake of iodide
400μg
How much iodide is in the thyroid and what form is it in?
2 month supply (7500μg) in the form iodothyronine (or thyronines)
What is the purpose of having such a large pool of iodide in the thyroid?
Protects from iodide deficiency for about 2 months