thryoid hormones

Question 1

What are the 2 thyroid hormones?

Answer 1

T3 (triiodothyronine), T4 (thyroxine)

Question 2

Which thyroid hormone is the more active form?

Answer 2

T3

Question 3

Which hormone acts of the the thyroid gland to trigger T3/T4 release?

Answer 3

Thyroid stimulating hormone (TSH)

Question 4

What are the steps in the production of the thyroid hormones in the thyroid gland?

Answer 4

1. thryoid gland absorbs iodine from the bloodstream
2. follicular cells synthesise thyroglobulin which is secreted into the colloid
3. iodine is bound to tyrosine residues on thryoglobulin, forming precursors to T3 and T4.
4. T3/T4 are formed and stored in thryoid follicles until they are released under the stimulation of TSH

Question 5

What is the main carrier protein for thyroid hormones?

Answer 5

Thyroxine-binding globulin

Question 6

What is the structure of T4?

Answer 6

Contains two DITs, which have a total of 4 iodines

Question 7

What is the structure of T3?

Answer 7

Contains a DIT and MIT, with a total of 3 iodines

Question 8

What is the relationship between free and bound thryoid hormones in the blood stream?

Answer 8

They are in a dynamic equilibrium. The unbound/free fraction is a small percentage but is physiologically active.

Question 9

What is the receptor binding of T3/T4?

Answer 9

They enter cells and bind to nuclear receptors to influence gene expression

Question 10

What are the metabolic functions of thyroid hormones?

Answer 10

Increase basal metabolic rate (raises body temperature), promotes oxygen consumption and energy production

Question 11

What is the role of thyroid hormones in infants/foetuses?

Answer 11

Nervous system development

Question 12

What are the negative feedback loops for thyroid hormones?

Answer 12

T3 and T4 have negative feedback to both the hypothalamus and anterior pituitary, reducing TRH and TSH release respectively

Question 13

What are the causes of hyperthyroidism?

Answer 13

Grave’s disease, toxic nodular goitre, thyroid adenoma, thyroiditis

Question 14

What is Grave’s disease?

Answer 14

An autoimmune disorder where the thyroid gland is stimulated by an abnormal immunoglobulins that have a TSH-like effect on TSH receptors causing excessive T4/T3 release.

Question 15

What is toxic multinodular goitre?

Answer 15

Nodules in the thyroid gland become able to synthesise and secrete T3/T4 independent of TSH receptor stimulation

Question 16

What is a toxic thyroid adenoma?

Answer 16

A benign tumor of the thyroid gland that produces excess T3/T4

Question 17

What is thyroiditis?

Answer 17

Inflammation of the thyroid gland, leading to the release of stored thyroid hormones into the bloodstream.

Question 18

What is T3 thyrotoxicosis?

Answer 18

Increased levels of free T3, but normal T4 and low TSH

Question 19

What are the symptoms of hyperthyroidism?

Answer 19

Weight loss, increased appetite, anxiety, tachycardia/palpitations, arrhythmias, insomnia, fatigue, exophthalmos, goitre, heat intolerance, excessive sweating

Question 20

What are the results of thyroid function tests in hyperthyroidism?

Answer 20

TSH is usually low, while T3/T4 are elevated

Question 21

What are the results of thyroid antibody panels in hyperthyroidism?

Answer 21

If caused by Grave’s Disease, will be positive for Thyroid stimulating antibodies

Question 22

What will be the result of a Radioactive Iodine reuptake test in Grave’s disease?

Answer 22

High, diffuse uptake

Question 23

What will be the result of a Radioactive Iodine reuptake test in thyroiditis?

Answer 23

Diffuse pattern of low uptake

Question 24

What will be the result of a Radioactive Iodine reuptake test in toxic multinodular goitre?

Answer 24

Focal uptake in thyroid nodules

Question 25

What will be the result of a Radioactive Iodine reuptake test in toxic adenoma?

Answer 25

‘Hot’ nodule - area of increased uptake

Question 26

What investigations can be used to diagnose hyperthyroidism?

Answer 26

thyroid function test, thyroid antibody panel, radioactive iodine reuptake test/scan, ultrasound

Question 27

What are the non-pharmacological interventions for hyperthyroidism?

Answer 27

full/partial thyroidectomy, Radioactive iodine therapy

Question 28

What are the pharmacological interventions for hyperthyroidism?

Answer 28

Anti-thyroid drugs (e.g. carbimazole), Beta-blockers for anxiety/arrhythmia

Question 29

What are the causes of hypothyroidism?

Answer 29

Hashimoto’s thyroiditis, Iodine deficiency, thyroidectomy/radioactive iodine therapy, pituitary dysfunction

Question 30

What is Hashimoto’s Thyroiditis?

Answer 30

An autoimmune condition that causes the destruction of the thyroid gland

Question 31

What dietary deficiency is associated with hypothyroidism and goitre?

Answer 31

Iodine

Question 32

What is primary hypothyroidism?

Answer 32

A condition where the thyroid is unable to produce thyroid hormone, despite high levels of TSH

Question 33

What is secondary hypothyroidism?

Answer 33

Low thyroid hormone release due to insufficient stimulation from low TSH levels

Question 34

What are some causes of primary hypothyroidism?

Answer 34

Hashimoto’s thyroiditis, iodine deficiency, thyroidectomy, drugs

Question 35

What are some causes of secondary hypothyroidism?

Answer 35

Lesion/stroke of pituitary gland destroying TSH secreting cells

Question 36

What are the symptoms of hypothyroidism?

Answer 36

fatigue, weight gain, reduced appetite, cold intolerance, dry skin, thinning hair, brittle nails, depression, constipation, bradycardia, muscle aches, puffy face, goitre, menstrual irregularities

Question 37

What are the results of thyroid function tests in hypothyroidism?

Answer 37

T3/T4 are low. TSH is high in primary, and low in secondary hypothyroidism

Question 38

What are the typical results of a thyroid anti-body panel in hypothyroidism?

Answer 38

If hypothyroidism is caused by Hashimoto’s will likely to positive for anti-thyroid peroxidase antibodies

Question 39

What is the appearance of a radioactive iodine reputake scan in primary hypothyroidism?

Answer 39

There will be diffuse, low uptake

Question 40

What is the appearance of a radioactive iodine reputake scan with a non-secreting thyroid nodule?

Answer 40

‘Cold’ nodule - nodule will have less uptake than the rest of the thyroid

Question 41

What are the treatments for hypothyroidism?

Answer 41

hormone replacement therapy (levothyroxine), iodine supplementation