thyroid hormones

Question 1

what cells secrete T3+4

Answer 1

thyroid follicular cells

Question 2

what cells secrete calcitonin

Answer 2

parafollicular C cells

Question 3

where is thyroglobulin produced and what does contain

Answer 3

in the thyroid follicular cells and released via exocytosis.

iodide -enough for 90 days worth of thyroid hormones

Question 4

where is Thyrotropin releasing hormone stored

Answer 4

hypothalamus

Question 5

where is thyroid stimulating hormone stored

Answer 5

anterior pituitary

Question 6

consequence of high t3 on TSH

Answer 6

low TSH = thyroid regression and reduced activity

Question 7

low t3 on TSH

Answer 7

high TSH = thyroid enlargement and increased activity

Question 8

what stimulates thyroid follicular cells to produce t3&4

Answer 8

TSH in the bloodstream
follicular cells have csr (GPC receptor) for TSH which activated adenylate cyclase to produce cAMP which activates functions

Question 9

how is iodide transported from the blood to the cells

Answer 9

via the sodium iodide symporter

2 sodium cations for each iodide anion

Question 10

how is iodide transported from the cells to the lumen

Answer 10

via the pendrin transporter which exchanges chloride ions for iodide ions

Question 11

what happens to iodide when in the lumen

Answer 11

it is oxidised to atomic iodine

Question 12

what enzyme covalently binds iodine to tyrosine residues in thyroglobulin

Answer 12

thyroid peroxidase

Question 13

which molecules make up t4

Answer 13

2 molecules of di-iodotyrosine

Question 14

which molecules make up t3

Answer 14

one DIT then one MIT

Question 15

which molecules make up reverse T3

Answer 15

MIT THEN DIT = inactive

Question 16

how is T3&4 released from the thyroglobulin backbone

Answer 16

subject to proteolysis via lysosomes in cells

Question 17

example of 2 hormones that are used to treat hypothyroidism

Answer 17

levothyroxine sodium t4

liothyronine sodium t3

Question 18

example of 2 drugs that are used to treat hyperthyroidism

Answer 18

carbimazole

propylthiouracil

Question 19

how can liver disease affect t thyroxine (t4) delivery

Answer 19

t4 is transported in the serum with specific binding protein which are synthesised in the liver. liver disease will decrease t4 transport to peripheral tissues.

Question 20

why is it difficult to transport thyroxine (t4)

Answer 20

it is insoluble in serum = hydrophobic

Question 21

why is t4 more abundant than t3

Answer 21

the binding ration of t4;t3 is

20;1 . transthyretin does not bind t3.

Question 22

which protein best binds t4

Answer 22

thyroxine binding globulin

Question 23

advantages of thyroxine finding globulin

Answer 23

prevents loss of t4 in urine

Question 24

which hormone is more active

Answer 24

t3 is biologically active. t4 is relatively inactive an so must be converted to t3

Question 25

how is t4 converted to t3

Answer 25

via iodothyronine deiodinases (DIO 1+2) which are selenocysteine-systeine containing enzymes. selenium accepts iodine so DIT–>MIT

Question 26

which deiodinases make reverse T3

Answer 26

DIO1+3

Question 27

where is DIO1 predominantly found

Answer 27

liver, kidney, muscle and thyroid

Question 28

where is DIO2 predominantly found

Answer 28

CNS, pituitary thyrotropes

Question 29

which hormone has the higher affinity to thyroid hormone receptors

Answer 29

t3 has a 15 fold affinity

Question 30

t3 can increase gene transcription eg

Answer 30

increase growth hormone

Question 31

t3 can decrease gene transcription e.g.

Answer 31

decrease prolactin

Question 32

give 5 biological actions of thyroid hormones (hint: word MM…)

Answer 32

MMCFG control of basal metabolic rate, musculoskeletal effects, cvd effects, foetal development, growth

Question 33

effect if thyroid hormone deficiency in foetal development

Answer 33

irreversible mental impairment and dwarfism, miscarriage, neonatal goiter,

Question 34

what is the effect of t3 on cardiovascular system

Answer 34

myocardial calcium uptake, increase in metabolism, vasodilation

Question 35

role of t3 in bone

Answer 35

simulator effect on bone turnover