Thyroid Hormone Flashcards
What type of receptor is TSHR?
TSHR is a G Protein coupled receptor. Coupled to both Gs and Gq G proteins.
Explain the pathways of TSH.
Gs = Activates cAMP pathway. Increases iodide uptake, TH release and gland growth
Gq = activates inositol phosphate/Ca pathway. Hormone synthesis
Explain iodide trapping
It refers to the active cotransport of circulating iodide with Na ions across the basolateral membranes where the Na ions are pumped out of the cell by Na/K ATPase. Thyroid follicle contains colloid within which thyroglobulin is embedded. Iodide is rapidly oxidized to iodine by thyroid peroxidase.
List some of the actions of thyroid hormone?
Metabolic actions. Effects lipid and carbohydrate metabolism. T3 stimulates CHO absorption from the small intestine. T3 is calorigenic (heat producing)
Permissive effects. T3 upregulates beta-adrenergic Rs in many tissues. Increases HR and FoC and potentiates the actions of catecholamines. T3 is also needed for the normal CNS development in children
What are thyroid function tests and how can levels be elevated/lowered?
1% of TH in the body is free hormone. Total T4/T3 assays measure the bound hormone.
Total T4 may be elevated in pregnancy, women taking CoCs. Total T4 may be low in congenital TBG deficiency or severe liver dx
What is Graves’ disease and its symptoms?
Its an autoimmune disease where thyroid follicular cells produce excessive amounts of T4 and T3 via the TSHR autoantibody.
Its characterized by a suppressed serum TSH level and a thyroid gland is symmetrically enlarged and its vascularity is increased.
Symptoms include increased BMR (weight loss, poor tolerance to heat), palpatations and exophthalmos.
What the management of Graves’ disease?
Thyroidectomy, using radioactive iodine to destroy the thyroid gland and inhibiting thyroid hormone synthesis.
What are causes and symptoms of hypothyrodism?
Causes include primary failure of the thyroid gland, inadequate dietary supply of iodine or 2ndary hypothyroidism.
Symptoms: excessive weight gain, easily fatigued, decreased BMR, slow weak pulse and slow reflexes and mental responsiveness.
What is myxoedema coma?
Untreated hypothyroidism. Hypoventilation, hypoglycaemia, yellowish skin and hoarse voice.
What is the difference between hasimoto’s disease and goitre?
HD: cells of the immune system attack thyroid tissue. Decreased TH due to decreased thyroid function.
G: thyroid gland is overstimulated. Occurs when TSH excessively stimulates the thyroid gland. Less negative feedback inhibition on the AP and hypothalamus. Increased size and number of follicular cells.
What is the MOA of levothyroxine and pharmacokinetic characteristics?
MoA is the same to that of endogenous T4. Absorption is increased when hormone is taken on an empty stomach. Protein binding is 99%
List 4 drug interactions of levothyroxine
Calcium supplements, aluminium hydroxide, cholestyramins, sucralfate, SERMs admin 2 hours before/after.
Why is liothyronine (T3) seldomly used?
Because of its short-half life and it requires multiple daily dosing and it does not increase T4, difficult to monitor treatment.
What is the MoA of propylthiouracil?
It inhibits deiodination of T4–> T3. It also causes hepatotoxicity.
What are some adverse effects of PTU?
Macropapular rash, arthralgia, fever, GI distress
