Thyroid Gland

Question 1

What is the major product of the thyroid gland

Answer 1

thyroxine (T4)

Question 2

The backbone of TH is _____ and is synthesized in the ____

Answer 2

thyroglobulin, rER

Question 3

Thyroglobulin is stored in ___

Answer 3

follicular colloid

Question 4

How does iodide enter thyroid follicular cells

Answer 4

thyroid follicular cells trap and concentrate iodide via Na/O- symporter in basal membrane

Question 5

How does iodide get into the colloid?

Answer 5

iodide is shuttled across the apical membrane by Cl-/I- transporter

Question 6

What is the key enzyme in the production of thyroid hormone

Answer 6

thyroperoxidase

Question 7

What are the three main rolls of thyroperoxidase

Answer 7

oxidize iodide to iodine
iodinate tyrosine melecules
condensation of MIT and DIT

Question 8

TSH stimulates what three actions in the thyroid

Answer 8

I- uptake
throglobulin synthesis
endocytosis of colloid

Question 9

How does methimazole work?

Answer 9

it inhibits TPO

Question 10

What are goitrogens

Answer 10

they are substances that disrupt production of thyroid hormones

Question 11

True/False: T4 is a prehormone for T3

Answer 11

true

Question 12

Where is most T3 producted

Answer 12

in tissues via deiodination of T4

Question 13

What are the three main binding proteins of TH

Answer 13

TBG, ALB, plasma lipoproteins

Question 14

Where is TGB produced

Answer 14

the liver

Question 15

what is the main TH binding protein in large animals and primates

Answer 15

TBG

Question 16

What is the main TH binding protein in small animals

Answer 16

ALB

Question 17

What TH binding protein has the highest affinity for T4?

Answer 17

TBG

Question 18

True/False: TBG has a higher affinity for T3 than T4

Answer 18

false, it has a higher binding affinity for T4

Question 19

How does estrogen, cortisol, and NSAIDS affect T4 protein binding?

Answer 19

estrogen increases binding while cortisol and NSAIDS compete for binding sites

Question 20

Typically with drug therapy (glucocorticoids and NSAIDS) fT4 is _____

Answer 20

cleared more rapidly due to the competitive binding initially yielding higher fT4 levels

Question 21

What are the two main factors that contribute to lower circulating T3 levels?

Answer 21

difference in TBG binding affinity and the difference in thyroid output

Question 22

True/False: TSH goal is to maintain fT4 levels

Answer 22

true

Question 23

with drug therapy (glucocorticoids, NSAIDS) bloodwork will show ____ fT4 values and ____ Total T4 values as compared to normal

Answer 23

normal, lower

Question 24

How does iodide concentration regulate thyroid hormone synthesis

Answer 24

excess iodide exerts negative feedback thus suppressing hormone synthesis

Question 25

What are the different deiodinases and what are their functions? where?

Answer 25

D1: T4 to T3 in most tissues D2: T4 to T3 in brain D3: main source of rT3

Question 26

True/False: a selenium deficiency will result in a decrease in T3 levels, why

Answer 26

True, because all deiodinases contain selenium so T4 wouldn't be able to be converted to T3

Question 27

What is the purpose of rT3

Answer 27

it helps lower metabolic rate

Question 28

What are three example of conditions where D3 activity may increase yielding increase in rT3

Answer 28

starvation, hibernation, illness

Question 29

What is the main basic function of TH?

Answer 29

it affects expression of ~1% of genes in target tissues

Question 30

What is the effect of TH on O2 consumption and metabolic rate

Answer 30

TH increases consumption of O2 and basal metabolic rate

Question 31

What three tissues O2 consumption is not affected by TH

Answer 31

spleen, brain, testes

Question 32

Why do hyperthyroid cats tend to display agitated/ hyperactive behavior?

Answer 32

because in adults, TH has an excitatory effect on the CNS

Question 33

TH is essential for what 3 things during fetal development

Answer 33

Brain development, synapse formation, myelination

Question 34

Fetal hypothyroidism can present with:

Answer 34

decreased mentation and reflexes stillbirths

Question 35

Why can you see angular limb deformaties in hypothyroid foals

Answer 35

because TH synergizes with GH and IGF-1 which promotes ossification, fusion of bone plates, and bone maturation

Question 36

If TH stimulates carbohydrate metabolism why does it not result in hyperglycemia

Answer 36

because it also enhances insulin dependent entry into cells

Question 37

True/False: plasma concentrations of cholesterol and TG are inversely correlated with thyroid hormone levels

Answer 37

true

Question 38

TH ____ EPO

Answer 38

stimulates

Question 39

True/false: TH increases beta:alpha adrenergic receptor ration

Answer 39

true

Question 40

What type of cardiovascular changes might you see in response to TH

Answer 40

vasodilation, increased HR, increased tissue profusion

Question 41

What is the affect of TH on the hair cycle

Answer 41

it initiates and maintains the anagen phase of the hair cycle

Question 42

What signs might you expect in a hypothyroid dog (4)?

Answer 42

anemia, hair loss, weight gain, heat seeking