Session 10- The Thyroid Gland Flashcards
Where is the thyroid
Lies against and around the front larynx and trachea
Below thyroid cartilage
What joins the two lobes of the thyroid
Isthmus
When does the thyroid gland appear
3-4 gestation it appears as an epithelial proliferation in the floor of pharynx at the base of the tongue
What are follicles filled with
Colloid- a deposit of thyroglobulin
How are thyroid hormones formed
2 tyrosines linked together with iodine at three or 4 positions on the aromatic rings
3- T3
4- T4
What is T3
Triiodothyronine
What is T4
Tetraiodothyronine
What is the scaffold on which thyroid hormones are. Formed
Thyroglobulin
What is thyroid peroxidase
Membrane bound enzyme that regulates 3 separate reactions involving iodide
1) Oxidation of Iodide to Iodine (requires the presence of H2O2)
2) Addition of Iodine to tyrosine acceptor residues
on the protein throglobulin
3) Coupling of MIT or DIT to generate thyroid
hormones within the thyroglobulin protein
How is iodine absorbed
It is reduced to iodide before absorption principally in the small intestine by a sodium-iodide symporter
How is thyroid hormone secretion regulated
Negative feedback
What are the 2 interconnected responses of thyroid hormone
- effects on cellular differentiation and development
- effects on metabolic pathways
What is Thyroid stimulating hormone
Glycoprotein hormone composed of 2 non-covalently bound sub-units
Triggers the release of thyroid hormone
What does TSH stimulate
- Iodine uptake
- iodide oxidation
- thyroglobulin iodination
- Thyroglobulin synthesis
- Colloid pinocytosis into cell
- proteolysis of thyroglobulin
- cell metabolism and growth
General actions of thyroid hormone
- increase in basal metabolic rate and heat production.
- stimulation of metabolic pathway
- sympathomimetic effects