Thyroid Gland Flashcards
(28 cards)
What is the functional unit of the Thyroid gland?
The follicle.
What is Colloid? What does it contain?
Colloid is the fliud inside a follicle, which contains Thyroglobulin (TG), which contains tyrosine.
What does the Thyroid gland look like? Where is it?
The thyroid gland is a bilobed gland, with the glands connected by the isthmus. It is just caudal to the Larynx.
What are the two most important thyroid hormones?
T3 - Triiodothyronine
T4 - Thyroxine
What is T3? What is it made from?
T3 is made from 1 x MIT and 1 x DIT. It is the biologically active thyroid hormone, and is secreted less than T4.
What is T4? What is it made from?
T4 is made from 2 x DIT. It is a circulating pro-hormone and is converted to T3 to be active. It is secreted in larger amounts than T3.
How do Thyroid hormones negatively feedback? Where do they do this?
T3 can feedback on both TSH and TRH. T4 has to be converted to T3 to feedback.
How are thyroid hormones synthesised?
TSH binds to GPCR, and increase cAMP. This phosphorylates iodide pump and brings in I. I and TG are combined by TPO. T3 and T4 made, they can then be endocytosed and T3 and 4 can be excreted.
What is thyroperoxidase? (TPO)
An enzyme present on the epithelial cells of follicles that aids iodide molecules and thyroglobulin joining to form T3 and T4.
When TSH binds to follicle epithelial cell, how does it initiate iodide pump?
It binds to GPCR, increases cAMP, which phosphorylates iodide pump.
What three carrier proteins can thyroid hormones be bound to in circulation?
Thyroid binding globulin (TBG), Thyroid binding pre-albumin (TBPA) or Albumin.
In the circulation, which hormone (bound or unbound) is responsible for hormonal activity?
Free hormone (unbound).
How do thyroid hormones act within their target cell?
They bind to Thyroid hormone receptor, which is attached to thyroid hormone responsive elements. This then influences the cell’s mRNA synthesis.
What happens when unliganded Thyroid receptor is not bound by thyroid hormone?
When T3 is not bound, Thyroid hormone receptor is attached to Corepressors, so it does not act.
What happens when liganded Thyroid receptor is not bound by thyroid hormone?
When T3 binds to Thyroid H receptor, dimerisation of retinoic acid attracts Coactivators and so it can act.
How does TRH cause the pituitary secretion of TSH?
TRH attaches to GPCR, and it increases intracellular calcium and increases phospholipase C, which increases glycosylation of TSH.
What are the main effects of thyroid hormones?
Innrease basal metabolic rate, Important for normal growth, changes from glucose metabolism to fat metabolism. Positive inotropes and chronotropes.
Where are the main sites of thyroid metabolism?
Liver, Brain, Muscle and Kidney.
How is T4 metabolised? (3)
1) Deiodinated into T3. 2) Converted into T3. 3) Conjugated and thus excreted.
What are C cells? What do they secrete?
C cells are in the thyroid gland, and they secrete Calcitonin. Calcitonin decreases blood calcium.
If there is a lack of thyroid hormone in late fetal life or early post-natal development, what issues does this rise?
Cretinism (mental retardation)
What are the clinical signs of Hypothyroidism?
Weight gain, Bradycardia, Myxoedema, Hyperkeratosis (Scaly), ‘Sad’ expression, Lower BMR, Infertility
What are the 3 main causes of Hypothyroidism?
Immune-mediated thyroiditis, Idiopathic Thyroid atrophy, Thyroid tumour (non-secreting).
What are the clinical signs of Hyperthyroidism?
Weight loss, Restless, nervous, tachycardia, Infertility
