Thryoid

Question 1

What does T3 stand for?

Answer 1

Liothyronine (tri-iodothyronine)

Question 2

What does T4 stand for?

Answer 2

Levothyroxine (thyroxine)

Question 3

What is the role of NIS on the basolateral surface of the thyroid follicular cell?

Answer 3

It’s a sodium-iodide symporter (2Na+ and 1I- in at the same time)

Question 4

What is the role of TSHR on the basolateral surface of the thyroid follicular cell?

Answer 4

To bind to TSH and allow mediation of it’s down-stream effects

Question 5

What is the role of PDS on the apical surface of the thyroid follicular cell?

Answer 5

This is the pendrin transporter for moving iodide into the colloid of the follicular cell

Question 6

What is the role of TPO on the apical surface of the thyroid follicular cell?

Answer 6

This is an oxidising enzyme involved in converting iodide into iodine in the colloid

Question 7

What is the role of DUOX1/DUOX2 on the apical surface of the thyroid follicular cell?

Answer 7

These molecules provide the oxidising agents for the oxidation of iodine by TPO by forming hydrogen peroxidase

Question 8

What is the role of IYD in the cytoplasm of the thyroid follicular cell?

Answer 8

It’s involved in the recycling of iodine by taking up unused MIT and DIT

Question 9

What is the role of the D1 and D2 enzymes in the thyroid follicular cell?

Answer 9

They convert T4 to the more active T3

Question 10

Where are D1 enymes located in thyroid follicular cells?

Answer 10

Near the basolateral membrane

Question 11

Where are D2 enymes located in thyroid follicular cells?

Answer 11

On the endoplasmic reticulum

Question 12

What happens when TSH binds to the TSH receptor on the thyroid follicular cells

Answer 12

stimulates the G-protein coupled receptor and causes action via two different pathways: cAMP mediated PKA pathway (AC) or inositol phosphate diacylglycerol pathway (PLC).
TSH binding stimulates increased expression of NIC, TPO, thyroglobulin and hydrogen peroxide synthesis by increasing activity of DUOX2 and DUOX2a, and it also increases the formation of the active T3 relative to T4.

Question 13

How many different types of deiodenase enzymes are there?

Answer 13

Three, D1, D2 and D3

Question 14

Where are D1 enzymes located and what is their function?

Answer 14

In the plasma membrane of the liver, kidney, muscle and thyroid gland and they are involved in producing T3 for the circulation from reversed T3 and T4

Question 15

Where are D2 enzymes located and what is their function?

Answer 15

They are found in the endoplasmic reticulum near the nucleus in the brain and pituitary gland and cause local T3 production from T4

Question 16

Where are D3 enzymes located and what is their function?

Answer 16

D3 enzymes are located in endoplasmic reticulum of the brain, placenta and foetus and are involved in the degradation of T3 into less active or inactive versions (enantiomers)

Question 17

How are D1 enzymes affected by hypo and hyperthyroidism?

Answer 17

In hypothyroidism D1 levels are reduced and in hyperthyroidism they are increased (may be due to the fact these receptors are actually present in the thyroid gland)

Question 18

How are D2 enzymes affected by hypo and hyperthyroidism?

Answer 18

Type 2 deiodinase in the brain is important to facilitate normal thyroid levels, and thus normal glucose metabolism, and therefore, in hypothyroidism the number and activity of the D2 receptors increases in order to compensate for the reduced thyroid hormone production, and the receptors at downregulated in hyperthyroidism in order to prevent the production of excess metabolic waste products.

Question 19

How are D3 enzymes affected by hypo and hyperthyroidism?

Answer 19

In hypothyroidism D3 is down regulated and in hyperthyroidism D3 is unregulated

Question 20

What thyroid pathology can lead to he development of atrial fibrillation?

Answer 20

Hyperthyroidism

Question 21

What are the effects of hyperthyroidism on the body?

Answer 21

Increased HR, increased BMR, catabolic state (breakdown), exophalmos of the eyes, pernicious anaemia, gynaecomastia and erectile dysfunction

Question 22

What is Graves’ disease?

Answer 22

In this condition an individual has antibodies which bind to the TSH receptor and causes the activation of the thyroid follicular cells and leads to hyperthyroidism. The risk factors for Graves disease include HLA status, infection, stress and being female.

Question 23

What may cause hyperthyroidism?

Answer 23

Graves disease

Question 24

What may cause thyrotoxicosis?

Answer 24

In this condition an individual has antibodies which bind to the TSH receptor and causes the activation of the thyroid follicular cells and leads to hyperthyroidism. The risk factors for Graves disease include HLA status, infection, stress and being female.

Question 25

How is thyrotoxicosis diagnosed?

Answer 25

Elevated T3/T4 and suppression of TSH

Question 26

What may cause hypothyroidism?

Answer 26

Hashimoto’s disease, endemic goitre, lithium, cabbage, infiltrative diseases, Pendred’s syndrome, hypopotuitarism

Question 27

What are the symptoms of hypothyroidism?

Answer 27

Dry and flaky skin and hair, carotaemia of the skin (yellow/orange tinge), bradycardia, cholesterol increase, reduced appetite, reduced GFR, normocytic anaemia, reduced libido, dementia, reduced BMR and decreased GLUT4 translocation

Question 28

How would primary hypothyroidism be diagnosed?

Answer 28

There would be a high TSH and a low T4

Question 29

How can pregnancy induce hypothyroidism?

Answer 29

Thyroid binding globulin increases in pregnancy, and therefore less free/active hormone and therefore this induces a hypothyroid state.