Lecture 22

Question 1

When is the thyroid gland visible/palpable?

Answer 1

When enlarged (here it is called a GOITRE)

Question 2

What is the clinical significance of a goitre?

Answer 2

Can compress structures causing issues with swallowing and breathing
-could be cancer

Question 3

What nerves are likely to be damaged during thyroid surgery?

Answer 3

Recurrent laryngeal
External branch of the superior laryngeal
(these supply the larynx which is involved in speech)

Question 4

What blood vessels supply the thyroid?

Answer 4

3 arteries and 3 veins
-superior, middle and inferior thyroid arteries/veins
It is a highly vascularised structure

Question 5

What is the most common cause of a giotre?

Answer 5

Iodine deficiency

Question 6

Why do you take iodine in pregnancy?

Answer 6

To ensure you don’t develop hypothyroidism which can lead to cretinism in children

Question 7

What is the size and weight of the thyroid?

Answer 7

2-3cm

Weighs 15-20g making it one of the largest endocrine glands in the body

Question 8

What are the 2 major cell types in the thyroid?

Answer 8

Follicular cells: arranged in follicles
Parafollicular cells (C cells): found in connective tissue separating the follicles

Question 9

What are the 3 hormones produced by the thyroid gland?

Answer 9

Thyroxine: T4
Triiodothyronine: T3
Calcitonin (via parafollicular cells)

Question 10

What amino acid are T3/4 derived from?

Answer 10

Tyrosine (tyrosine residues on thyroglobulin add iodine)

Question 11

How long does the store of T3/4 last in the lumen of the follicles?

Answer 11

Several months

2-3 months

Question 12

Once T3/4 are cleaved from thyroglobulin how do they reach target tissues?

Answer 12

They diffuse from the epithelial cells into circulation

Question 13

Where is TRH released from?

Answer 13

Dorsomedial nucleus of the hypothalamus under the influence of circulating levels of T3/4 (negative feedback), stress, and temperature

Question 14

What is TSH stimulated by and where from?

Answer 14

Stimulated by TRH from hypothalamus. TSH is released from thyrotropes in the anterior pituitary. TSH travels in the blood to affect the follicular cells of the thyroid gland

Question 15

What rhythm does TSH release follow?

Answer 15

Diurnal rhythm, higher levels at night decreasing in the early hours of the morning

Question 16

What trophic effects does TSH have?

Answer 16

-increased vascularity
-increase in size and number of follicle cells
Can result in a goitre

Question 17

Are T3/4 hydrophobic/hydrophilic?

Answer 17

Hydrophobic

Question 18

Does T3/4 have a lower affinity for transport proteins?

Answer 18

T3, therefore there is a higher % of free T3 and its half life is therefore shorter

Question 19

What increases the synthesis of TBG (thyroxine binding protein)?

Answer 19

Oestrogen during pregnacy, producing a fall in the amount of free T3/4as more is bound, therefore more TSH/TRH are produced and the thyroid gland secretes more T3/4
(therefore the amount of free T3/4 returns to normal but the total amount in the blood is increased)

Question 20

What specific effects do T3/4 have on certain tissues?

Answer 20

• directly affect bone mineralisation (physical growth)
• increase synthesis of heart muscle protein
• CNS: hyperplasia of cortical neurones (in cerebral cortex) and myelination

Question 21

What are some indirect actions of T3/4?

Answer 21

Stimulate hormone and neurotransmitter receptor synthesis in variety of tissues (heart/GI) producing an increased responsiveness
-tachycardia
-increased bowel motility
Permissive role in actions of FSH and LH, therefore ovulation fails to occur in absence of TH (period)

Question 22

Do target receptors have a greater affinity for T3/4?

Answer 22

T3

Question 23

What does increased protein synthesis due to activation of transcription factors by T3/4 mean?

Answer 23

Increased production of specific functional proteins, leading to increased cell activity and increased demand in energy

Question 24

How is T4 converted to T3?

Answer 24

Removal of the 5 prime iodine

Question 25

What does the removal of the 3 prime iodine on T3 cause?

Answer 25

Produces rT3, an inactive reverse which can bind to TH receptors without stimulating them, blocking the effect of T3

Question 26

What is Hashimoto’s disease?

Answer 26

Autoimmune disease mostly affecting women, resulting in destruction of the thyroid follicles/ production of an antibody which blocks the TSH receptor on follicle cells preventing them from responding to TSH
=Hypothyroidism
-low T3/4
-high TSH/TRH

Question 27

How are patients with Hashimoto’s disease treated?

Answer 27

With oral thyroxine- levothyroxine (thyroxine replacement therapy)

Question 28

What is Grave’s disease?

Answer 28

Form of hyperthyroidism mostly in women, autoimmune disease where antibodies (thyroid stimulating immunoglobulin-TSI) stimualte TSH receptors on follicle cells resulting in more T3/4.
-high T3/4
-low TSH/TRH
TSH levels fall due to negative feedback but doesn’t effect TH as TH secretion is due to the TSI rather than TSH

Question 29

How do you treat Grave’s disease?

Answer 29

Carbimazole: inhibits incoorperation of iodine into thyroglobulin by inhibiting thyroid peroxidase
-beta blockers can be used to dampen sympathetic system: can cause agranulocytosis: neutropenia: risk of infections

Question 30

Symptoms of hypothyroidism:

Answer 30

• cold intolerance
• reduced BMR
• weight gain
• tiredness
• bradycardia
• neuromuscular system (weakness, cramps, cerebellar ataxia: clumsiness of movement)
• dry, flaky skin
• alopecia
• voice is deep
• mixed oedema
• goitre
• bulging eyes (as autoimmune antibodies attack back of eyes)

Question 31

Symptoms of hyperthyroidism:

Answer 31

• heat intolerance
• increased oxygen consumption
• increased BMR
• weight loss
• physical and mental hyperactivity
• tachycardia
• intestinal hypermobility
• skeletal and cardiac myopathy
• osteoporosis due to increased bone turnover

Question 32

Does the thyroid gland move?

Answer 32

Yes it moves upon swallowing

Question 33

Where would you find a thyroglossal cyst?

Answer 33

In the midline of the throat

Question 34

What is borderline hypothyroidism?

Answer 34

Normal T4/3 but high TSH

Question 35

Symptoms of Hashimoto’s disease?

Answer 35

• loss of lateral 1/3 of eyebrow

- carpel tunnel syndrome due to fluid retention, pressure on median nerve

Question 36

What is myxeoedema?

Answer 36

Swelling around eyes and skin

Question 37

Symptoms of Grave’s disease?

Answer 37

• pretibial myxoedema (autoantibodies affect skin in shin)

- clubbing of nail beds

Question 38

What damage can removal of thyroid gland surgically have?

Answer 38

Damage to parathyroid glands and therefore calcium homeostasis

Question 39

When does a nodule in the thyroid appear cancerous?

Answer 39

• single nodule
• rapid enlargement of lump in neck
• family history of thyroid cancer
• hard/irregular feeling
• lymphnodes present

Question 40

How could you determine if a thyroid lump was cancerious or not?

Answer 40

Do a biopsy with ultrasound. Take cells via biopsy to investigate them
-if cancerous you can surgically remove

Question 41

How do you image the thyroid?

Answer 41

Ultrasound
X ray
CT

Question 42

What is an ethical issue with thyroid drugs?

Answer 42

They can be abused

Question 43

What is lingual thyroid?

Answer 43

Thyroid tissue in tongue, didn’t migrate fully

Question 44

What is myxoedema coma?

Answer 44

Hypothermia and fluid overload in heart: severe hypothyroidism in elderly

Question 45

What is thyroid crisis/storm?

Answer 45

Hyperpyrexia, tachycardia, cardiac failure

=urgent treatment (hyperthyroidism)

Question 46

Why do you have to be careful if pregnant with Grave’s disease?

Answer 46

Antibodies can cross the placenta and baby can be born with hyperthyroidism