Topic 7.3

Question 1

Which trace element is necessary for normal thyroid hormone synthesis?

Answer 1

Iodine

Question 2

What is the functional unit of the thyroid gland?

Answer 2

Thyroid follicle

Question 3

What fills the follicular lumen?

Answer 3

Colloid

Question 4

What is colloid made of?

Answer 4

thyroglobulin

Question 5

What cells can we find scattered in the thyroid gland?

Answer 5

parafollicular, C cells

Question 6

What do C cells secrete?

Answer 6

Calcitonin (peptide hormone)

Question 7

Where does the start of thyroid hormone synthesis happen?

Answer 7

extracellularly

Question 8

3 types of iodo-thyronines

Answer 8

• T4, thyroxine, 3,5,3’,5’-tetra-iodothyronine
• T3, 3,5,3’-tri-iodothyronine
• Reverse T3, 3,3’,3’-tri-iodothyronine

Question 9

3 transporters useful for iodine transportation

Answer 9

• Na/I transporters (NIS)
• Na+,K+, ATPase
• Pendrin : I/Cl

Question 10

What molecule stimulates expression of the NIS?

Answer 10

TSH

Question 11

What does thyroid peroxidase catalyze? (3)

Answer 11

• iodide oxydation
• thyroglobulin iodination
• iodothyronine coupling

Question 12

Where is thyroid peroxidase located?

Answer 12

in the apical membrane

Question 13

What is T3 a coupling of?

Answer 13

DIT + MIT

Question 14

What is T4 a coupling of?

Answer 14

DIT + DIT

Question 15

First step of synthesis of iodothyronines

Answer 15

Iodide is oxidized and incorporated into tyrosine residues w/in thyroglobulin in the lumen

Question 16

What is the electron acceptor of the follicular membrane?

Answer 16

H202

Question 17

When is thyroglobulin degraded?

Answer 17

Once endocytotic vesicle fuses with lysosome, then there’s proteolysis

Question 18

Which enzyme catalyzes deioniodination of MIT and DIT?

Answer 18

iodo-tyrosine deiodinase

Question 19

What is peripheral conversion?

Answer 19

T4 is converted into active T3

Question 20

Which enzymes catalyze peripheral conversion?

Answer 20

tyrosine-specific deiodinases

Question 21

Where can we find Type 1 deiodinase? (3)

Answer 21

• Liver
• Kidneys
• Thyroid gland

Question 22

Where can we find Type 2 deiodinase?

Answer 22

glial cells of the CNS

Question 23

Roles of type 2 deiodinase (2)

Answer 23

• Maintains intracellular T3

- mediates T4 to feedback on secretion of TSH

Question 24

What receptors do thyroid hormones use to act?

Answer 24

Nuclear receptors

Question 25

Structure of nuclear receptor (3)

Answer 25

• Variable region
• DNA binding domain
• Hormone binding domain

Question 26

What happens to T4 once it enters its target cell?

Answer 26

Most of it is converted to T3 by 5’/3’-monodeiodinase

Question 27

Where do tyrosine receptors bind on DNA?

Answer 27

thyroid response elements (TRE) in the promoter region

Question 28

How much of the tyrosine bound to receptor is T3?

Answer 28

90%

Question 29

6 effects of thyroid hormones

Answer 29

• increased BMR
• increased thermogenesis
• decreased plasma [glycerol] and [cholesterol] but increased plasma [FA]
• Increase gluconeogenesis and glycogenolysis
• Growth
• increased cardiovascular effects

Question 30

What is TRH?

Answer 30

thyrotropin releasing hormonone

Question 31

What does TRH bind to?

Answer 31

Gq coupled receptor on the thyrotrophic membrane

Question 32

What does TSH bind to?

Answer 32

Gs coupled receptors on the thyroid follicular cells

Question 33

What inhibits TSH release? (2)

Answer 33

• SST

- Dopamine

Question 34

What is hypothyroidism often due to

Answer 34

Autoimmunity : hashimoto’s disease

Question 35

What is Grave’s disease?

Answer 35

Autoimune disease in which thyroid stimulating immunoglobulins form against the TSH receptor in the thyroid gland : continual activation