Thyroid

Question 1

T3/T4 are synthesized by what?

Answer 1

Thyroid follicle (central lumen specifically)

Question 2

What is the thyroid follicle?

Answer 2

Thyrocytes (follicular cells) with central lumen

Question 3

Calcitonin is synthesized by what?

Answer 3

Parafollicular cells

Question 4

T3/T4 consist of?

Answer 4

Thyroglobulin and iodide

Question 5

What is “iodide trapping”?

Answer 5

Thyroid stimulating hormone promotes intake of iodide into follicular cells

Question 6

Where is thyroglobulin produced?

Answer 6

Follicular cell

Question 7

What does thyroid stimulating hormone also stimulate?

Answer 7

Reuptake of T3/T4 back into cell to be released from thyroid gland

Question 8

What percent of T3/T4 binds to thyroxine binding globulin

Answer 8

70%

Question 9

What percent of T3/T4 binds to other protein carriers?

Answer 9

29%

Question 10

What percentage of circulating T3/T4 is free T3?

Answer 10

0.3%

Question 11

What percentage of circulating T3/T4 is free T4?

Answer 11

0.03%

Question 12

What is “circulating storage” of T3/T4?

Answer 12

T3/T4 that is bound to carrier proteins
(inactive)

Question 13

What happens when there is too much free T3/T4?

Answer 13

Hypothalamus releases less TRH and the anterior pituitary gland releases less TSH

Question 14

What happens when there is too little free T3/T4?

Answer 14

Hypothalamus releases more TRH and the anterior pituitary gland releases more TSH

Question 15

Which thyroid hormone is directly used by body tissue?

Answer 15

T3

Question 16

How is T4 used by body tissue?

Answer 16

Metabolised in to T3 first

Question 17

What enzyme converts T4 into T3 in cells?

Answer 17

D2

Question 18

What does D2 monitor?

Answer 18

That there is enough free T3 readily available in the cell

Question 19

What enzyme converts T4 into T3 in the liver/kidneys?

Answer 19

D1

Question 20

What does D1 monitor?

Answer 20

That there is enough available free T3 in the plasma

Question 21

What enzyme deactivates T3/T4?

Answer 21

D3

Question 22

When T4 is deactivated what is it converted into?

Answer 22

rT3

Question 23

When T3 is deactivated what is it converted into?

Answer 23

T2

Question 24

What does D3 monitor?

Answer 24

That there isn’t too much T3/T4 in the plasma

Question 25

How do thyroid hormones affect metabolism?

Answer 25

Stimulate energy consumption and metabolism which increases body temperature

Question 26

Thyroid hormones are ___________ with the sympathetic nervous system

Answer 26

synergistic

Question 27

How do thyroid hormones affect growth and development?

Answer 27

Critical for CNS and skeletal development Works w/ growth hormone and reproductive hormones

Question 28

Insufficient thyroid hormones in newborns can cause?

Answer 28

Irreversible skeletal and neurological impairment

Question 29

What are the target tissues of thyroid hormones?

Answer 29

Heart, liver, pancreas, CNS, bones, adipose, GI tract

Question 30

How do thyroid hormones affect the heart?

Answer 30

Increases HR and cardiac output T3 increases sensitivity to sympathetic system (epinephrine)

Question 31

How do thyroid hormones affect the pulmonary system?

Answer 31

Stimulate the brainstem to increase ventilation

Question 32

How do thyroid hormones affect adipose tissue?

Answer 32

Stimulate lipolysis

Question 33

How do thyroid hormones affect the liver?

Answer 33

Stimulate glycogenolysis, gluconeogenesis, ketogenesis, synthesis of VLDL

Question 34

How do thyroid hormones affect the pancreas?

Answer 34

Directly stimulate alpha and beta cells to produce glucagon and insulin

Question 35

How do thyroid hormones affect the CNS?

Answer 35

Increase CNS neuron sensitivity/excitability Stimulate neuron growth and development

Question 36

What is the "critical window" for newborns in. regards to diagnosing thyroid hormone insufficiency?

Answer 36

2 weeks Sooner the DX/TX the better the outcome

Question 37

How do thyroid hormones affect the bones?

Answer 37

Promotes bone growth Stimulates osteoblast and osteoclast activity (homeostasis)

Question 38

Hypothyroidism is linked with increased risk of?

Answer 38

Osteoporosis

Question 39

How do thyroid hormones affect the GI tract?

Answer 39

Increases GI secretions and motility which promotes glucose absorption

Question 40

What is the Wolff-Chaikoff Effect?

Answer 40

High plasma iodide levels will decrease secretion of T3/T4