59 - Thyroid Function in Health and Disease

Question 1

Roles of thyroid gland
1
2

Answer 1

• Secrete thyroid hormones to regulate metabolism

* Secrete calcitonin to regulate calcium levels

Question 2

Structure of thyroid gland

Answer 2

Two lobes, joined by an isthmus below larynx

Question 3

Alternative name of T4

Answer 3

Thyroxine

Question 4

Where in the thyroid gland are T3 and T4 made?

Answer 4

Colloid

Question 5

Structure of the thyroid
1
2
3

Answer 5

• Follicular cells surrounding colloid
• Colloid (glycoprotein mix) contains thyroglobulin (Tg)
• C cells in interstitial spaces secrete calcitonin
– Calcium metabolism

Question 6

Proportion of T3 derived from T4

Answer 6

80%

Question 7

Are thyroid hormones lipophilic or hydrophilic?

Answer 7

Lipophilic

Question 8

Majority of thyroid hormones produced by the thyroid

Answer 8

T4 (90%)

Question 9

Most potent of the thyroid hormones

Answer 9

T3 (tri-iodotyrosine)

Question 10

Receptor for thyroid hormones

Answer 10

Nuclear

Question 11

Whole-body effects of THs

Answer 11

Increase in O2 consumption (thermogenesis)
Protein catabolism in adults.
Anabolism in children.
Normal development of the nervous system.

Question 12

Action of THs at cellular level

Answer 12

Increases activity of metabolic enzymes and Na+/K+ ATPase

Question 13

Only stimulus that increases TRH levels

Answer 13

Cold temperatures (only in infants)

Question 14

Where do T3 and T4 negatively feedback?

Answer 14

Both on hypothalamus (inhibits tonic release of TRH) and anterior pituitary (TSH release)

Question 15

Half life of THs

Answer 15

About 1 day for T3

6-7 days for T4

Question 16

Binding proteins of THs in the blood

Answer 16

Thyroxine-binding globulin and albumins

Question 17

Main actions of THs
1
2
3

Answer 17

• Increase BMR & oxygen consumption
– Calorigenic / heat producing effects
• Modulate metabolism
• Sympathomimetic effect; Increase heart rate, cardiac
output

Question 18

Developmental roles of THs
1
2
3

Answer 18

• Not essential for life but essential for child
growth & development
• Growth promoting
– Fetal life
– After birth essential for GH & IGFs actions
• Nervous system development
– Before & after birth

Question 19

Hormone levels in primary hypothyroidism and iodine deficiency

Answer 19

Decreased T3, T4, increased TSH

Question 20

Most common endocrine illness

Answer 20

Hypothyroidism (1-2% of adults, more common in women than men)

Question 21

Hormone levels in secondary hypothyroidism

Answer 21

Decreased T3, T4, decreased TSH, can have decreased TRH

Question 22

Hypothyroidism without a goitre

Answer 22

Secondary hypothyroidism (EG: from hypothalamic or anterior pituitary failure/tumour)

Question 23

Physiological effects of hypothyroidism
1
2
3
4
5

Answer 23

– Decrease BMR & O2 consumption, decrease energy, increase weight
– Cold intolerance
– Sympathetic effects, decrease heart rate
– Central effects, decrease mentation & reflexes, fatigue
– Decrease protein synthesis, accumulate mucopolysaccharides under skin
= puffy appearance of myxedema

Question 24

Causes of congenital hypothyroidism

1-5

Answer 24

1) Maternal iodine deficiency
2) Foetal thyroid dysgenesis
3) Inborn errors of thyroid hormone synthesis
4) Maternal antithyroid antibodies cross placenta
5) Foetal hypopituitary hypothyroidism

Question 25

Hormonal signs of primary hyperthyroidism

Answer 25

High T3 and T4, decreased TSH

Question 26

Most common cause of primary hyperthyroidism

Answer 26

Grave’s disease (60-80% of cases)

Question 27

Gender in which Grave’s disease is more common

Answer 27

Women

Question 28

Hormonal signs of secondary hyperthyroidism, from hypothalamic or anterior pituitary excess

Answer 28

High T3 and T4, high TSH, +/- high or low TRH

Question 29

Hormonal signs of secondary hyperthyroidism from a hypersecreting tumour of the thyroid

Answer 29

Increased T3 and T4, decreased TSH.

No goitre.

Question 30

Physiological effects of hypethyroidism
1
2
3

Answer 30

– Increased BMR & O2 consumption, increased appetite, weight loss, muscle weakness, heat intolerance, increased heart rate
– Increased alertness, irritability, hyperexcitability
– Graves’ disease exophthalmos = bulging eyes

Question 31

What leads to exophthalmos in Grave’s disease?

Answer 31

Water retaining carbohydrates behind eyes

Question 32

Treatment of hyperthyroidism
1
2
3

Answer 32

– remove thyroid / tumour
– use radioactive iodine to destroy gland
– Anti thyroid drugs
• block TH synthesis or conversion T4 to T3

Question 33

How does goitre occur in hypothyroidism?

Answer 33

Decreased T3 and T4 from low iodine.

No negative feedback onto anterior pituitary.
Ant pit releases TSH, hyperstimulating thyroid

Question 34

How does a goitre occur in hyperthyroidism?

Answer 34

Thyroid stimulating immunoglobulins hyperexcite thyroid.