thyroid

Question 1

what is T3?

Answer 1

tri-iodothyronine

Question 2

what is T4?

Answer 2

thyroxine

Question 3

what does T3 and t4 do?

Answer 3

work together to regulate how body uses energy

Question 4

which is active in T3 and T4?

Answer 4

• T4 is a reserve and converted to active T3

Question 5

how do thyroid hormones travel in body?

Answer 5

hyroid hormones are bound to proteins in circulation eg thyroxine binding globulin (TBG)

Question 6

what are normal levels of T4?

Answer 6

T4 – 100nmol/L total, free = 20pmol/L

Question 7

what are normal levels of T3?

Answer 7

T3 – total – 2nmol/L and free = 5pmol/L

Question 8

what does the thyroid do?

Answer 8

• Produces and stores thyroid hormones and sequesters iodine from blood

Question 9

which cells produce thyroid hormones?

Answer 9

follicular cells

Question 10

what do c cells produce?

Answer 10

• C cells (parafollicular) produce calcitonin

Question 11

can shape and size of thyroid cells change?

Answer 11

• Size of follicles changes with the amount of stored material

Question 12

how is iodine taken up into follicular cells?

Answer 12

1. Iodine is taken into follicular cells by a TSH sensitive pump

Question 13

what happens to iodine when taken into follicular cells?

Answer 13

2. Iodine diffuses to follicle cavity, where thyroglobulin (containing T3 and T4) are exocytosis and then endocytosed
3. Lysosomal digestion breaks down the thyroglobulin molecule and T3 and T4 are endocytosed out the cell

Question 14

how are T3 and T4 majority in the blood stream?

Answer 14

4. T3 and T4 bind to TBG, transthyretin or albumin and are in blood stream

Question 15

what detects disturbance T3/4 homeostasis?

Answer 15

• Disturbances homeostasis are detected by hypothalamus – this releases TRH
• TSH is the secreted which is secreted to thyroid gland
  TSH stimulates TH synthesis – requires tyrosine and iodine

Question 16

how do is iodine intake ensured?

Answer 16

• Iodination of salt of 150ug/day – salt now contains iodine in developing countries to prevent this problem

Question 17

what does thyroid hormone do to CVS?

Answer 17

• Increase HR, SV, CO and contractility of myocardium
• Moderate vasodilator to blood and tissues

Question 18

what does thyroid hormone do to cell turnover?

Answer 18

• Promote cell turnover and metabolic activity in reproductive system – fertility

Question 19

how is thyroid essential in development and growth?

Answer 19

• Essential for nomrla brain development in utero and growth in children
• Perceived energy levels and higher cognition
• Stimulate mitochondrial replication and activity
• Increase cellular demand for glucose

Question 20

what does calcitonin do?

Answer 20

• Calcitonin acts to reduce extracellular calcium in blood
• Inhibits osteoclast activity
• Stimulates renal excretion of calcium

Question 21

what does corticosteroids interact with?

Answer 21

inhibit TSH production/ release. Inhibit TBG production

Question 22

how does dopaminergic drugs affect thyroid?

Answer 22

inhibit TSH production/ release

Question 23

how does lithium affect thyroid?

Answer 23

inhibit T3/T4 production

Question 24

how does carbimazole affect thyroid?

Answer 24

inhibit T3/ T4 production

Question 25

how does oestrogen affect thyroid?

Answer 25

increase TBG (thyroxine binding globulin) and TSH

Question 26

what is TBG?

Answer 26

thyroxine binding globulin

Question 27

how does androgens affect thyroid hormones?

Answer 27

: inhibit T3 and T4 production

Question 28

how does beta blockers affect thyroid?

Answer 28

decrease T4 to T3 conversion – not a primary method of management

Question 29

what thyroid levels are seen in hyperthyroidism?

Answer 29

• High T4
• High T3
• Low TSH

Question 30

what thyroid levels are seen in hypothyroidism?

Answer 30

• Low T4
• Low T3
• High TRH