Exam 3- Physiology of the Thyroid Gland and Thyroid Hormones

Question 1

thyroid hormone synthesis starts with synthesis of _______________

Answer 1

thyroglobulin

Question 2

tetraiodothyronin (thyroxine; T4) is produced from __________

Answer 2

tyrosine

Question 3

what do thyroid follicular cells do to iodide?

Answer 3

trap and concentrate it via Na/I symporter in basal membrane

Question 4

how does iodide get into the colloid?

Answer 4

chloride/iodide transporter in apical membrane

Question 5

what does thyroperoxidase (TPO) do?

Answer 5

oxidizes I- (iodide) to iodine
iodinates tyrosine molecules
produces monoiodotyrosine (MIT) and diiodotyrosine (DIT), thyroid hormone precursors

Question 6

after making MIT and DIT, what does thyroperoxidase do?

Answer 6

cleaves and couples MIT or DIT to acceptor DIT residues

Question 7

thyroperoxidase actions result in a mixture of ___, ___, ___, and ___ attached to the thyroglobulin backbone

Answer 7

MIT
DIT
T3
T4

Question 8

how do the final thyroid hormones get into the blood?

Answer 8

diffuse through basal membrane after being cleaved

Question 9

what mediates synthesis and secretion of thyroid hormone?

Answer 9

thyroid stimulating hormone: receptors on basal membranes, G protein mediated increase in cAMP

Question 10

what does thyroid stimulating hormone stimulate?

Answer 10

I- uptake
thyroglobulin synthesis
endocytosis of colloid

Question 11

what is most of the hormone released from the thyroid gland?

Answer 11

thyroxine (T4)

Question 12

from where is most of the T3 in serum derived?

Answer 12

deiodination of T4 in tissues

Question 13

is T3 or T4 more metabolically active?

Answer 13

T3

Question 14

why is thyroid hormone bound?

Answer 14

prolongs the circulating half life and controls the blood hormone levels

Question 15

what proteins bind thyroid hormone?

Answer 15

thyroid hormone-binding globulin (TBG)
albumin
plasma lipoproteins

Question 16

how does estrogen affect thyroid hormone-binding globulin (TBG)?

Answer 16

increases: increases total T4

Question 17

how do cortisol and NSAIDS affect thyroid hormone levels?

Answer 17

compete for binding sites: lower total levels because cause it to be cleared more

Question 18

what regulates thyroid hormone?

Answer 18

hypothalamus and central nervous system

Question 19

how does heat affect TRH?

Answer 19

decreased by heat
increased by cold

Question 20

true/false: excess iodide exerts negative feedback on thyroid hormone synthesis

Answer 20

true

Question 21

do deiodinases differ by tissue?

Answer 21

yes

Question 22

what does thyroid hormone (T3) bind to in the nucleus?

Answer 22

heterodimer with retinoid X receptor

Question 23

what is thyroid hormone essential for in development?

Answer 23

brain
synapse formation
myelination

Question 24

what does thyroid hormone do with erythropoiesis?

Answer 24

stimulates it

Question 25

what cell organelles are necessary for making thyroglobulin?

Answer 25

rER makes backbone Golgi glycosylates and packages

Question 26

what stimulates the synthesis of thyroglobulin?

Answer 26

thyroid stimulating hormone

Question 27

what percent of the body's iodide is in the thyroid?

Answer 27

>90%

Question 28

where is coupling done?

Answer 28

thyroglobulin backbone

Question 29

what are goitrogens?

Answer 29

substances that disrupt production of thyroid hormones

Question 30

what is used to treat hyperthyroid cats?

Answer 30

methimazole

Question 31

what percent of the body's T3 is produced by the thyroid?

Answer 31

20%

Question 32

what is the sequence for control of thyroid hormone?

Answer 32

thyrotropin releasing hormone from hypothalamus thyroid stimulating hormone from thyrotropes in anterior pituitary increased T4 release from thyroid negative feedback from T4 to both hypothalamus and anterior pituitary

Question 33

how does cortisol affect thyroid stimulating hormone?

Answer 33

inhibits its secretion

Question 34

does iodide exert negative feedback on thyroid hormone?

Answer 34

yes: iodination thyroglobulin, thyroid hormone synthesis, and sensitivity to TSH

Question 35

what is the thyroid nuclear receptor specific for?

Answer 35

T3

Question 36

where is deiodinase 1 (D1) specific to?

Answer 36

liver, kidneys, thyroid, pituitary

Question 37

what deiodinase is the main source of rT3?

Answer 37

D3

Question 38

what deiodinase is specific to the brain?

Answer 38

D2 astroglia

Question 39

what substance is essential to iodinases?

Answer 39

selenium

Question 40

when is deiodinase 3 (D3) more active?

Answer 40

sustained catabolism periods (starvation, illness, hibernation) fetus

Question 41

what does thyroid receptor do in the absence of hormone?

Answer 41

binds to co-repressor proteins that silence gene expression

Question 42

what is the thyroid receptor?

Answer 42

heterodimer with retinoid X receptor

Question 43

what does thyroid hormone do to the daily energy use?

Answer 43

increases it free fatty acids mobilized and used Na/K ATPase stimulated increased body heat

Question 44

what does thyroid hormone synergize with in a young animal?

Answer 44

growth hormone and IGF-1

Question 45

how does thyroid hormone stimulate carbohydrate metabolism?

Answer 45

facilitates gluconeogenesis: enhances effects cortisol, epinephrine, growth hormone, glucagon facilitates glycogenolysis enhances absorption carbohydrates in intestine enhances insulin-dependent entry into cells

Question 46

what does thyroid hormone do with fat metabolsm?

Answer 46

increases lipolysis increases cholesterol synthesis, excretion in bile, and lipoprotein catabolism increases triglyceride turnover and chylomicron clearance

Question 47

what does thyroid hormone do with the beta:alpha-adrenergic receptor ratio?

Answer 47

increases beta-adrenergic receptors