AF and the Thyroid Flashcards

Question

what are the primary hormones secreted by the thyroid gland

Answer 1

Tri-iodothyronine (T3) and tetra-iodothyronine (T4, thyroxine)

Answer 2

1. Follicular cell synthesises enzymes and thyroglobulin for colloid - thyroglobulin is a protein which has lots of tyrosine moieties attached to it - together, these proteins are exocytosed, so vesicle will fuse with the membrane and release its contents into colloid

Answer 3

2. I- will enter follicular cells using co-transporter and Na+ - net neutral charge (+ ion coin in for every - ion) - doesn't change potential within the cell Then, I- is pumped out across basal membrane of follicular cells into colloid

Answer 4

3. Iodine binds with tyrosines and combine to form T3 and T4 and the molecule is now endocytosed back into follicular cells

Answer 5

4. Enzymes work on that molecule to free up thyroglobulin, so it can be exocytosed back into colloid

Answer 6

5. Intracellular enzymes separate T3 and T4 from the protein

Answer 7

6. Free T3 and T4 then pass out of the follicular cell, into the bloodstream, where they are transported to their site of action

Answer 8

1. Tyrosine combines with a single iodide atom to form mono-iodotyrosine 2. or it combines 2 iodide atoms to form di-iodotryrosine - if you combine one that's bound 2 with another that's bound 2, you can form T4

Answer 9

Thyroid hormones are insoluble in water, so are transported in blood bound to plasma proteins

Answer 10

over 99% of circulating thyroid hormones are protein bound and 95% is T4 as half life in plasma is 6-8 days (more stable) and T3 is only 1 day

Answer 11

Majority of T4 binding is to thyroxine binding globulin (TBG) - 15-20% is bound to thyroxine binding pre albumin (TBPA) - 5-10% is bound to albumin (tends to be biologically inactive, so we need to free up that hormone for it to become biologically active) - only free (unbound) hormone is biologically active

Answer 12

1. T3 and T4 are pumped into cells using carrier mediated transport 2. T4 is generally biologically inactive and so once its inside the cell, it is converted to T3 by an enzyme that removes 1 of the iodide ions 3. That T3 then gets transported into the nucleus where it binds to thyroid hormone receptors that can then affect gene transcription and translation 4. Beta adrenergic receptor is affected as stimulation of beta receptors increases heart rate

Answer 13

1. increases protein synthesis and metabolic activity in cells 2. Increases body metabolism and body heat 3. Increases Beta 1 receptors 4. Increases heart rate and stroke volume 5. Increases cardiac output and blood pressure 6. Increases GI motility and GI secretions 7. Increases Neurogenesis, myelination and synaptogenesis 8. Increases dendrite formation and sympathetic activity 9. INcreases proliferation of skin cells and sweat and skin secretions 10. Increases hair and nail growth

Answer 14

1. the main effect of thyroid hormones is to increase basal metabolic rate 2. causes increase in carbohydrate metabolism 3. increases synthesis, mobilisation and degradation of lipids 4. increases protein synthesis 5. essential for the normal development of the CNS, especially myelination of nerve fibres

Answer 15

an increase in the number and size of mitochondria and an increased activity of metabolically important enzymes -so respiratory chain, ATP production and metabolic rate is increased

Answer 16

all aspects of carbohydrate metabolism are increased - glycogenesis and glucose uptake by muscle cells and adipose cells - potentiation of the effects of insulin - potentiation of the effects of the catecholamines - increase in glucose absorption by the GIT

AF and the Thyroid Flashcards

(41 cards)