thyroid

Question 1

what stimulates the thyroid follicles

Answer 1

TSH from pituitary gland binding to TSHR on basolateral membrane

Question 2

what does TSH stimulate the thyroid follicles to do

Answer 2

synthesis and release of protein hormone thyroglobulin and enzyme thyroporoxidase into the colloid from apical membrane; iodide uptake from blood and release into colloid; uptake and transport of T3 and T4 by lysozymes from the colloid into the blood

Question 3

how is iodide taken up from blood into follicular cells to do

Answer 3

through NIS (sodium/iodide active cotransporter)

Question 4

in the nucleus what is incorporated into thyroglobulin

Answer 4

tyrosyl residues

Question 5

what happens within the colloid

Answer 5

iodination of tyrosine in thyroglobulin to form mono/di-iodotyrosine, catalysed by thyroporoxidase and H2O2

Question 6

what is the coupling reaction

Answer 6

where mono/di-iodotyrosine are coupled to form T3/T4, catalysed by thyroporoxidase and H2O2

Question 7

what are thyroid hormones also called

Answer 7

iodothyronines

Question 8

examples of mono-iodotyrosine thyroid hormones

Answer 8

tyrosine, 3-monoiodotyrosine

Question 9

examples of di-iodotyrosine thyroid hormones

Answer 9

3,5-diiodotyrosine

Question 10

what T3 thyroid hormone do tyrosine and 3-monoiodotyrosine react to form

Answer 10

3,5,3’-tri-iodothyronine

Question 11

what T4 thyroid hormone do two 3,5-diiodotyrosine moleucles react to form

Answer 11

3,5,3’,5’-tetra-iodothyronine

Question 12

what is 3,5,3’,5’-tetra-iodothyronine also known as

Answer 12

thyroxine

Question 13

what is the fate of T3 and T4 thyroid hormones

Answer 13

taken up by lysosomes in follicular cells and released into the blood

Question 14

how are thyroid hormones transported in the blood

Answer 14

mostly bound to plasma proteins, <1% is unbound and bioactive

Question 15

give three thyroid hormone binding plasma proteins

Answer 15

thyroid-binding globulin, albumin, prealbumin

Question 16

what is the bioactive form of thyroid hormone

Answer 16

T3

Question 17

how can bioactive T3 also be produced

Answer 17

deiodination of T4

Question 18

what is reverse T3 and how is it produced

Answer 18

deactivated T3 where T4 is deiodinated in a different position

Question 19

where does deiodination occur

Answer 19

target tissues

Question 20

what is T3 mechanism of action

Answer 20

gene transcription in nucleus (up/down regulated), metabolic activity and non-nuclear actions on ion channels

Question 21

where is the T3 receptor

Answer 21

nucleus

Question 22

T3 actions: children

Answer 22

foetal growth and development

Question 23

T3 actions: adults

Answer 23

increase basal metabolic rate; increase protein, carbohydrate and fat metabolism, causing weight loss; potentiate actions of catecholamines (e.g. adrenaline causing tachycardia, lipolysis); have effects on GI, CNS and reproductive systems

Question 24

thyroxine essentiality

Answer 24

essential for normal brain development

Question 25

define cretin

Answer 25

child born with no thyroxine