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1. Endocrine > Thyroid hormone physiology > Flashcards

Thyroid hormone physiology Flashcards

1
Q

What cell synthesises hormones?

A

follicular cells

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2
Q

What is needed for the synthesis of T3 and T4?

A

iodine

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3
Q

Describe the synthesis of T3 and T4?

A

absorbed into the cell by iodine transporters (sodium-iodine symporter)
iodine attached to tyrosine residues on thyroglobulin to form MIT and DIT

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4
Q

What is the real name of MIT?

A

monoiodothyrosine

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5
Q

What is the real name of DIT?

A

di-iodothyrosine

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6
Q

What amounts of MIT and DIT make up T3?

A

MIT + DIT

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7
Q

What amounts of MIT and DIT make up T4?

A

DIT + DIT

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8
Q

Where is T3 and T4 stored before it is required?

A

colloid thyroglobulin

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9
Q

What percentage of hormone secreted is the highest - T3 or T4?

A 
T4 = 90%
T3 = 10%
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10
Q

Is T3 or T4 more potent?

A

T3

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11
Q

Are T3 and T4 hydrophobic or hydrophilic?

A

hydrophilic/lipophilic

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12
Q

How is T4 converted to T3?

A

by the liver

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13
Q

Which is more biologically active - T4 or T3?

A

T3

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14
Q

What do T3 and T4 bind to in blood?

A

plasma binding proteins e.g. thyroxine binding globulin, thyroxine binding prealbumin, albumin

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15
Q

What form of T3 and T4 is avaliable to tissues?

A

unbound form

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16
Q

How do the thyroid hormones affect sympathetics?

A

increase responsiveness to adrenaline and noradrenaline by increasing the number of receptors

17
Q

What stimulates the release of T3 and T4?

A

thyroid stimulating hormone

18
Q

How are T3 and T4 activated?

A

removing iodine

- occurs in liver and kidney

19
Q

What is the role of deiodinase enzymes?

A

take part in the activation and deactivtion of thyroid hormones

20
Q

Where are deiodinase enzymes found?

A 
in liver and kidney
heart and skeletal muscle
CNS
fat 
thyroid and pituitary
foetal tissues, placenta
21
Q

How does TSH bind to TRH?

A

on the surface of thyroid epithelial cells

22
Q

What happens after TSH had bound to TRH?

A

G proteins are activated which convert GTP –> GDP and produce cAMP
cAMP increases the production and release of T3 and T4

23
Q

What is the thyroid picture in primary hypothyroidism?

A

low T3&4

high TSH

24
Q

What is the thyroid picture in primary hyperthyroidism?

A

high T3&4

low TSH

25
Q

What is the thyroid picture in secondary hypothyroidism?

A

low T3&4

low/normal TSH

26
Q

What is the thyroid picture in secondary hyperthyroidism?

A

high T3&4

high/normal TSH

27
Q

What is the normal TSH values?

A

4mU/L

28
Q

What is the normal free T4 values?

A

9.8-18.8 pmol/L

29
Q

Why do goitres form?

A

reduced T3/T4 production causes a rise in TSH that causes a gland enlargment

1. Endocrine (32 decks)

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