Thyroid - Normal and Diseased

Question 1

Describe the thyroid-pituitary/hypothalamic axis. (including negative feeback loop)

Answer 1

The T4 and T3 in peripheral tissues would suppress secretion of both thyroid-releasing hormone and thyroid-stimulating hormone

Question 2

Describe the embryology of the thyroid gland.

Answer 2

Migrates down from base of tongue to in front of trachea splits via thyroglossal duct, forming left and right lobe joined by isthmus

Question 3

What hormones are produced in thyroid?

Answer 3

T3, T4, calcitonin; parathyroid hormone by parathyroid

Question 4

What is the arterial supply of thyroid?

Question 5

Describe the basic functional unit of thyroid

Question 6

What are the molecular features of thyroxine (T4) and tri-iodothyronine (T3)?

Question 7

Describe biosynthesis of thyroid hormones

Answer 7

6 steps!

Colloid and follicular cells
Colloid – synthesis of thyroglobulin; addition of iodine onto thyroglobulin to form MIT and DIT
Follicular cells – uptake of iodide, oxidising into iodine, iodine then transported into colloid

MIT + DIT –> T3
DIT + DIT –> T4 (thyroxine)

Question 8

T3 & T4

Answer 8

Thyroxine make up 90% of thyroid hormones
Triiodothyronine makes up 10%

T3 is 4 times more potent than T4
T4 can be converted to T3 by liver & kidney

T3 is the active form, T4 is more of a storage

Question 9

How are thyroid hormones regulated by TSH?

Question 10

What is the role of thyroglobulin?

Answer 10

as a precursor to form thyroid hormones

Question 11

What is the role of thyroxine and what are the biological effects of thyroid hormones?

Answer 11

On neurones and all cells - increased metabolic rate
*Carb/lipid/protein metabolism
On liver
On lungs
On heart

Question 12

How are thyroid hormones degraded?

Answer 12

De-iodinases

Predominantly degraded by D1

Question 13

How are thyroid hormones transported in plasma?

Answer 13

They are almost entirely bound by plasma proteins (thyroid binding hormones)

Question 14

What are some thyroid hormone dysfunctions?

Answer 14

Hyperthyroidism
- Everything is going fast, anxiety

Hypothyroidism
- tend to get weight gain, constipation, lower mood, fatigue

Question 15

Primary and secondary failure of thyroid causing hypothyroidism

Answer 15

Primary gland failure - may be associated with enlarged gland (goitre)

Secondary to TRH or TSH (no goitre)

Question 16

Myoxesim and

Question 17

Common cause of hyperthyroidism and symptoms?

Answer 17

Increased BMR

Question 18

What are observations in primary hypothyroidism and hyperthyroidism?

Answer 18

1st hypo: low T3, low T4, high TSH
1st hyper: high T3, high T4, low TSH

Question 19

What are observations of secondary hypothyroidism/hyperthyroidism? (hypothalamic/pituitary disease)

Answer 19

2nd hypo: low T3/T4, TSH low (or normal)
2nd hyper: high T3/T4, TSH high (or normal) –> loss of negative feedback

Question 20

What is myxoedema and pretibial myxoedema?

Answer 20

Myxoedema –> severe hypothyroidism
Pretibial myxoedema –> rare clinical sign of Grave’s disease (an autoimmune thyroid disease that result in HYPERthyroidism!)

Question 21

What are causes of primary hypothyroidism?

Answer 21

Goitrous
Non-goitrous
Self-limiting

Question 22

What is autoimmune hypothyroidism and what are characteristics of it?

Answer 22

Autoimmune destruction of thyroid gland

Antibodies against thyroid peroxidase (TPO)
T-cell infiltrate and inflammation microscopically

Question 23

What are clinical features of hypothyroidism? (very systemic)

Question 24

What are autoantibodies relevant in thyroid disease?

Question 25

How is hypothyroidism managed?

Answer 25

levothyroxine (T4)

Question 26

What is myxoedema coma? (extreme of HYPOthyroidism)

Answer 26

Mortality up to 60%

Complete slow down of metabolic rates

Co-existing adrenal failure in 10% patients (as hypothyroidism can be very frequently autoimmune, it is very likely that Addison’s go along with it)

Question 27

What is thyrotoxicosis and hyperthyroidism?

Answer 27

Thyrotoxicosis is the clinical, physiological and biochemical state arising when the tissues are exposed to excess thyroid hormone

Hyperthyroidism refers specifically to conditions in which overactivity of the thyroid gland leads to thyrotoxicosis

Question 28

What are symptoms of thyrotoxicosis?

Answer 28

Vision -
*lid retraction
*double vision
*proptosis (Grave’s)

Question 29

What conditions are associated with hyperthyroidism?

Question 30

What is Grave’s disease and what are investigation findings of the condition?

Answer 30

positive TSH autoantibodies (TRAb)
Young patients, particularly females

Question 31

What are clinical signs specific to Grave’s?

Answer 31

Thyroid eye disease (you cannot see white above cornea usually, but their eye balls are very protruding due to oedematous eye muscles)

Question 32

What is nodular thyroid disease?

Answer 32

negative TRAb antibodies

Older patients
More insidious onset
Thyroid may feel nodular

Question 33

What is thyroid storm? (extreme of HYPERthyroidism)

Question 34

how is hyperthyroidism treated?

Answer 34

antithyroid drugs - inhibition of thyroid peroxidase (TPO) thereby blocking thyroid hormone synthesis
*Carbimazole or propylthiouracil

beta-blockers
*Propranolol

Radioiodine

Question 35

What are subclinical thyroid diseases?

Answer 35

Abnormal

Question 36

What is sick euthyroid syndrome?