Thyroid gland

Question 1

What is the developmental function of the thyroid?

Answer 1

→ CNS and bone

Question 2

What is the metabolic function of the thyroid?

Answer 2

→ Essential for normal metabolism of many body tissues

Question 3

What are the 2 main branches that supply the thyroid?

Answer 3

→ Inferior thyroid artery - subclavian

→ Superior thyroid artery - carotid

Question 4

What are the hormonally active thyroid cells?

Answer 4

→ Follicular cells

Question 5

What cells secrete calcitonin and what does it do?

Answer 5

→ C cells

→ Reduces plasma calcium

Question 6

What is thyroid hormone derived from?

Answer 6

→ two iodinated tyrosine molecules

Question 7

What are the two forms of thyroid hormone?

Answer 7

→ Tri iodothyronine (T3)

• active form
• converted in target cells
• binds to receptor and exerts its effects

→ Thyroxine T4

• major form released into blood
• less active

Question 8

What is reverse T3?

Answer 8

→ Iodinated on a different side

→ Inactive

Question 9

How does iodide diffuse into the cell?

Answer 9

1) uptake of iodide from the circulation via Na+- I- pump on basolateral side
2) iodiode diffuses out into the colloid via a pendrin exchanger
3) At the extracellular apical membrane iodine is oxidized to iodine and bound to tyrosine

Question 10

What happens to iodide at the apical membrane?

Answer 10

1) At the extracellular apical membrane iodine is oxidized to iodine and bound to tyrosine
(this requires thyroid peroxidase and hydrogen peroxidase)

2) T4 and T3 are formed from di or mono iodinated thyroglobulin

Question 11

How are T3 and T4 brought back into the cell?

Answer 11

1) TSH stimulates colloid droplets with thyroid hormones within the thyroglobulin chain are taken back up into the cell via pinocytosis

Question 12

How is thyroglobulin separated from T3 and T4?

Answer 12

→ Colloid droplets fuse with lysosomes causing hydrolysis of thyroglobulin and the release of T3 and T4

Question 13

How is most of the thyroid hormone found in the circulation?

Answer 13

→ Bound to plasma protein

→ mainly thyroid binding globulin

Question 14

What is the most abundant form of thyroid hormone?

Answer 14

→ T4

Question 15

What is the family of thyroid hormone receptors ?

Answer 15

→ Nuclear receptors

Question 16

What does the thyroid receptor have a higher affinity for?

Answer 16

→ High affinity for T3

Question 17

What does the thyroid receptor activation require?

Answer 17

→ Dimerization

→ with another TR or a RXR

Question 18

What genes are thyroid receptors encoded by?

Answer 18

→ TR alpha

→ TR beta

Question 19

What do nuclear receptors consist of?

Answer 19

→ DNA binding domain
→ Hormone binding domain
→ Transcription factor binding domain

Question 20

What do D2 enzymes convert?

Answer 20

→ T4 into T3

Question 21

What do D3 enzymes do?

Answer 21

→ Inactivates T3 by converting it to T2 (inactive)

→ T4 into reverse T3 (inactive)

Question 22

What do you need to make D enzymes?

Answer 22

→ Selenium

Question 23

How does thyroid hormone get into cells?

Answer 23

→ Transporters such as MCT8

Question 24

What do mutations in MCT8 gene cause?

Answer 24

→ Allan hernon dudley syndrome

→ Associated with psychomotor retardation

Question 25

How does TH increase metabolic rate?

Answer 25

→ Increases number and size of mitochondria
→ Enzymes in the metabolic chain
→ Increases Na/K+/ATPase
→ Positive inotropic and chronotropic effects
→ Synergizes with sympathetic nervous system

Question 26

How does TH act on the energy metabolism?

Answer 26

→ Antagonizes insulin signalling partially

→ Gluconeogenesis and lipolysis are stimulated

Question 27

How is TH made?

Answer 27

→ Parvocellular neurons in hypothalamus release TRH (thyrotrophin releasing hormone) into the median eminence carried by the portal vein to the anterior pituitary

→ TRH stimulates thyrotrophs of the anterior pituitary to secrete TSH

Question 28

What 2 factors stimulate the hypothalamus to produce TH?

Answer 28

→ Stress

→ Cold

Question 29

What is an indicator of congenital hypothyroidism ?

Answer 29

→ HIGH TSH

Question 30

Why is high TSH and high TRH indicative of HYPOthyroidism?

Answer 30

→ If thyroid isn’t producing T3 or T4
→ There is no negative feedback because more needs to be made
→ TRH and TSH concentration are high

Question 31

What does lack of inhibition the equivalent of?

Answer 31

→ Stimulation

Question 32

What is the TSH receptor ?

Answer 32

→ A GPCR

Question 33

What are the main effects of the TSH receptor?

Answer 33

→ Iodide uptake
→ transcription of NIS, TG and TPO
→ Stimulates thyroid growth
→ Stimulates the uptake of colloid

Question 34

What is goitre?

Answer 34

→ Swelling of the thyroid gland

Question 35

What is euthyroid?

Answer 35

→ Normal function

Question 36

What is primary hyperthyroidism?

Answer 36

→ Thyroid gland is the problem

Question 37

What is secondary hyperthyroidism?

Answer 37

→ Problem in the pituitary

Question 38

What is the diagnosis for low TRH and low TSH but high T4 and T3?

Answer 38

→ Primary hyperthyroidism

Question 39

What is the diagnosis for high TRH & TSH but low T4 and T3?

Answer 39

→ Primary hypothyroidism

Question 40

What is the diagnosis for low TRH, high TSH and high T4 and T3?

Answer 40

→ Secondary hyperthyroidism

Question 41

What is Graves disease?

Answer 41

→ Autoimmune
→ High TH
→ Low TSH
→ Primary hyperthyroidism

Question 42

What are the symptoms of Graves disease?

Answer 42

→ weight loss
→ Tachycardia
→ Fatigue 
→ Goitre
→ Opthalmopathy

Question 43

What binds to the TSH receptor?

Answer 43

→ antibodies stimulate the production of TSH

Question 44

What is Hashimotos disease?

Answer 44

→ Autoimmune
→ Low TH
→ High TSH

Question 45

What are symptoms of hashimotos?

Answer 45

→ Lethargy
→ Intolerance to cold
→ Lack of growth and development
→ Diffuse goitre